Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Kohei Ohta Last modified date:2019.06.17

Associate Professor / Department of Bioresource Sciences / Faculty of Agriculture


Papers
1. Suzuki S, Nakanishi S, Tamminen M, Yokokawa T, Sato-Takabe Y, Ohta K, Chou HY, Muziasari WI, Virta M, Occurrence of sul and tet(M) genes in bacterial community in Japanese marine aquaculture environment throughout the year: Profile comparison with Taiwanese and Finnish aquaculture waters., The Science of the total environment, 669, 649-656, 2019.06.
2. Mohammad Ali Noman Reza, Sipra Mohapatra, Sonoko Shimizu, Shin Ichi Kitamura, Shogo Harakawa, Hidemasa Kawakami, Kei Nakayama, Eitaro Sawayama, Takahiro Matsubara, Kohei Ohta, Tapas Chakraborty, Molecular cloning, characterization and expression analysis of complement components in red sea bream (Pagrus major) after Edwardsiella tarda and red sea bream Iridovirus (RSIV) challenge, Fish and Shellfish Immunology, 10.1016/j.fsi.2018.08.027, 82, 286-295, 2018.11, The complement system plays an important role in immune regulation and acts as the first line of defense against any pathogenic attack. To comprehend the red sea bream (Pagrus major) immune response, three complement genes, namely, pmC1r, pmMASP and pmC3, belonging to the classical, lectin and alternative complement cascade, respectively, were identified and characterized. pmC1r, pmMASP, and pmC3 were comprised of 2535, 3352, and 5735 base mRNA which encodes 732, 1029 and 1677 aa putative proteins, respectively. Phylogenetically, all the three studied genes clustered with their corresponding homologous clade. Tissue distribution and cellular localization data demonstrated a very high prevalence of all the three genes in the liver. Both bacterial and viral infection resulted in significant transcriptional alterations in all three genes in the liver with respect to their vehicle control counterparts. Specifically, bacterial challenge affected the pmMASP and pmC3 expression, while the viral infection resulted in pmC1r and pmC3 mRNA activation. Altogether, our data demonstrate the ability of pmC1r, pmMASP and pmC3 in bringing about an immune response against any pathogenic encroachment, and thus activating, not only one, but all the three complement pathways, in red sea bream..
3. Tapas Chakraborty, Sipra Mohapatra, Megumi Tobayama, Kayoko Ohta, Yong Woon Ryu, Yukinori Kazeto, Kohei Ohta, Linyan Zhou, Yoshitaka Nagahama, Takahiro Matsubara, Hatching enzymes disrupt aberrant gonadal degeneration by the autophagy/apoptosis cell fate decision, Scientific Reports, 10.1038/s41598-017-03314-7, 7, 1, 2017.12, Environmental stressors, gonadal degenerative diseases and tumour development can significantly alter the oocyte physiology, and species fertility and fitness. To expand the molecular understanding about oocyte degradation, we isolated several spliced variants of Japanese anchovy hatching enzymes (AcHEs; ovastacin homologue) 1 and 2, and analysed their potential in oocyte sustenance. Particularly, AcHE1b, an ovary-specific, steroid-regulated, methylation-dependent, stress-responsive isoform, was neofunctionalized to regulate autophagic oocyte degeneration. AcHE1a and 2 triggered apoptotic degeneration in vitellogenic and mature oocytes, respectively. Progesterone, starvation, and high temperature elevated the total degenerating oocyte population and AcHE1b transcription by hyper-demethylation. Overexpression, knockdown and intracellular zinc ion chelation study confirmed the functional significance of AcHE1b in autophagy induction, possibly to mitigate the stress effects in fish, via ion-homeostasis. Our finding chronicles the importance of AcHEs in stress-influenced apoptosis/autophagy cell fate decision and may prove significant in reproductive failure assessments, gonadal health maintenance and ovarian degenerative disease therapy..
4. Eitaro Sawayama, Shiho Tanizawa, Shin Ichi Kitamura, Kei Nakayama, Kohei Ohta, Akiyuki Ozaki, Motohiro Takagi, Identification of Quantitative Trait Loci for Resistance to RSIVD in Red Sea Bream (Pagrus major), Marine Biotechnology, 10.1007/s10126-017-9779-z, 19, 6, 601-613, 2017.12, Red sea bream iridoviral disease (RSIVD) is a major viral disease in red sea bream farming in Japan. Previously, we identified one candidate male individual of red sea bream that was significantly associated with convalescent individuals after RSIVD. The purpose of this study is to identify the quantitative trait loci (QTL) linked to the RSIVD-resistant trait for future marker-assisted selection (MAS). Two test families were developed using the candidate male in 2014 (Fam-2014) and 2015 (Fam-2015). These test families were challenged with RSIV, and phenotypes were evaluated. Then, de novo genome sequences of red sea bream were obtained through next-generation sequencing, and microsatellite markers were searched and selected for linkage map construction. One immune-related gene, MHC class IIβ, was also used for linkage map construction. Of the microsatellite markers searched, 148 and 197 were mapped on 23 and 27 linkage groups in the female and male linkage maps, respectively, covering approximately 65% of genomes in both sexes. One QTL linked to an RSIVD-resistant trait was found in linkage group 2 of the candidate male in Fam-2014, and the phenotypic variance of the QTL was 31.1%. The QTL was closely linked to MHC class IIβ. Moreover, the QTL observed in Fam-2014 was also significantly linked to an RSIVD-resistant trait in the candidate male of Fam-2015. Our results suggest that the RSIVD-resistant trait in the candidate male was controlled by one major QTL closely linked to the MHC class IIβ gene and could be useful for MAS of red sea bream..
5. Sipra Mohapatra, Tapas Chakraborty, Mohammad Ali Noman Reza, Sonoko Shimizu, Takahiro Matsubara, Kohei Ohta, Short-term starvation and realimentation helps stave off Edwardsiella tarda infection in red sea bream (Pagrus major), Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology, 10.1016/j.cbpb.2017.01.009, 206, 42-53, 2017.04, Dietary regime modifications have been an integral part of health and healing practices throughout the animal kingdom. Thus, to assess the effects of periodic starvation and refeeding schedule on the physiological and immunological perturbations in Edwardsiella tarda infected red sea bream, we conducted a 20�day experiment using 4 treatment groups, namely, pre-fed placebo (PFP); pre-starved placebo (PSP); pre-fed infected (PFI); and pre-starved infected (PSI), wherein a 5�h E. tarda infection was done on the 11th day. In the present investigation, the pre-starved groups showed significant (P�<�0.05) alterations in the liver Hexokinase and Glucose-6-phosphatase activity. The pre-starved fish also exhibited significant (P�<�0.05) increment in the hepatosomatic index, along with increased hepatic glycogen content, in a time dependent fashion. The PPAR (peroxisome proliferator activated receptors)α transcription in the pre-starved group decreased significantly (P�<�0.05) by 10dai, while the PPARγ showcased a reverse pattern. The transcription of Hepcidin1 and Transferrin (iron homeostasis related genes), and Cathepsin D and Ubiquitin (programmed cell death related genes) portrayed a time responsive decrease and increase in PSI and PFI groups, respectively. Additionally, in comparison to the PFI group, the PSI fish demonstrated substantially reduced oxidative stress level. Fluorescent Immunohistochemistry showed significant (P�<�0.05) increase in p63 positive cells in the 10dai PFI fish in relation to the PSI group. Therefore, these findings provide new insight into the beneficial role of alternating starvation and refeeding schedule, preferably short-term starvation prior to an infection, in order to obtain better capability to battle against E. tarda infection in red sea bream..
6. Sato-Takabe, Y, Nakao, H, Kataoka, T, Yokokawa, T, Hamasaki, K, Ohta, K, Suzuki, S, Abundance of Common Aerobic Anoxygenic Phototrophic Bacteria in a Coastal Aquaculture Area, Front. Microbiol., 10.3389/fmicb.2016.01996, 7, 2016.12.
7. Ito, M, Ito, K, Ohta, K, Hano, T, Onduka, T, Mochida, K, Fujii, K, Evaluation of bioremediation potential of three benthic annelids in organically polluted marine sediment, CHEMOSPHERE, 10.1016/j.chemosphere.2016.08.046, 163, 392-399, 2016.11.
8. Mana Ito, Katsutoshi Ito, Kohei Ohta, Takeshi Hano, Toshimitsu Onduka, Kazuhiko Mochida, Transcription of a novel P450 gene varies with some factors (pollutant exposure, temperature, time, and body region) in a marine oligochaete (Thalassodrilides sp.), Marine Pollution Bulletin, 10.1016/j.marpolbul.2016.05.055, 109, 1, 344-349, 2016.08, Cytochrome P450 (CYP) enzymes play important roles in the metabolism of exogenous compounds such as polycyclic aromatic hydrocarbons (PAHs). A novel, full-length CYP gene (CYP4V30) was identified in the oligochaete Thalassodrilides sp. CYP4V30 mRNA expression was studied in worms exposed to PAH-polluted (Σ16PAHs; 37441 ng/g dry weight) or unpolluted (Σ16PAHs; 19 ng/g dry weight) sediment. CYP4V30 expression was much higher in worms exposed to contaminated sediments than in those exposed to unpolluted sediments at some temperatures (20 and 25 °C) and exposure durations (11-fold increase at 20 °C, 10-day exposure), but not at 15 °C or other exposure durations (P < 0.05). CYP4V30 mRNA expression was higher in the middle of the body than in the posterior (P < 0.05). The variation in transcriptional response with exposure time, temperature, and body region indicates that these factors should be considered when monitoring marine sediment pollution..
9. Sipra Mohapatra, Tapas Chakraborty, Rami Haj-Kacem, Sonoko Shimizu, Takahiro Matsubara, Kohei Ohta, Starvation: An Alternate Measure to Improve Immunity and Physiology of Red Sea Bream During Edwardsiella Tarda Infection., Journal of Aquaculture Research and Development, 10.4172/2155-9546.S2-007, 007, 2016.06, Dietary restrictions during infectious challenges are quite common in animal kingdom. In the present investigation, we aimed to explore the positive implications of short-term starvation in Edwardsiella tarda infected red sea breams. Starvation resulted in depleted transcription of several iron binding protein (Hepcidin, Transferrin), which could have reduced the bacterial colonization in starved- infected fish. This was confirmed by the significantly (P<0.05) low bacterial load in the spleen and muscle of starved-infected fish. Gills showed mild damage to the secondary filaments architecture as well as elevated mucus production in the starved-infected fish compared to the fed ones. Massive mucus cell hyperplasia was observed in starved-placebo fish, which further increased after infection. Decreased activities of serum anti-oxidative enzymes and reduced total antioxidant capacity after starvation was suggestive of improved stress response and heightened stress withstanding capacity of these fish. Relatively higher haemoglobin and phagocytic activity along with the increased cytokines (TNFα, IL- 1β) level in starved-infected groups than their fed counterparts indicated the better immune condition of the former group. Additionally, our data also demonstrated that starvation enhanced the survivability and overall disease resistance index of infected fish, indicating that short period of starvation might be a beneficial measure to fight against infections..
10. Ito, K, Ito, M, Onduka, T, Ohta, K, Torii, T, Hano, T, Mochida, K, Ohkubo, N, Miura, T, Fujii, K, Differences in the ability of two marine annelid species, Thalassodrilides sp and Perinereis nuntia, to detoxify 1-nitronaphthalene, CHEMOSPHERE, 10.1016/j.chemosphere.2016.02.026, 151, 339-344, 2016.05.
11. Wada, N, Horiuchi, N, Ohta, K, Urasaki, S, Yamauchi, K, Yamashita, K, Controlled in Vivo Nacre Formation in Flat Pearls with Hydroxyapatite Bioceramic Nuclei, CRYSTAL GROWTH & DESIGN, 10.1021/acs.cgd.5b01074, 16, 1, 167-173, 2016.01.
12. Mohapatra, S, Chakraborty, T, Shimizu, S, Urasaki, S, Matsubara, T, Nagahama, Y, Ohta, K, Starvation beneficially influences the liver physiology and nutrient metabolism in Edwardsiella tarda infected red sea bream (Pagrus major), COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY A-MOLECULAR & INTEGRATIVE PHYSIOLOGY, 10.1016/j.cbpa.2015.07.003, 189, 1-10, 2015.11.
13. Mohapatra, S, Chakraborty, T, Miyagawa, S, Zhou, L, Ohta, K, Iguchi, T, Nagahama, Y, Steroid responsive regulation of IFN gamma 2 alternative splicing and its possible role in germ cell proliferation in medaka, MOLECULAR AND CELLULAR ENDOCRINOLOGY, 10.1016/j.mce.2014.10.012, 400, C, 61-70, 2015.01.
14. M. Anisur Rahman, Kohei Ohta, Michiyasu Yoshikuni, Yoshitaka Nagahama, Hisashi Chuda, Michiya Matsuyama, Characterization of ovarian membrane receptor for 17,20β-dihydroxy-4-pregnen-3-one, a maturation-inducing hormone in yellowtail, Seriola quinqueradiata, General and Comparative Endocrinology, 10.1016/S0016-6480(02)00026-6, 127, 1, 71-79, 2002.01, In our previous studies, we tentatively identified 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) as a maturation-inducing hormone (MIH) in yellowtail (Seriola quinqueradiata) through in vivo and in vitro experiments. In this study, we investigated the binding sites for radioactive 17,20β-P and characterized the receptor binding to the ovarian plasma membrane in yellowtail undergoing first stage of maturation (FSM). Equilibrium binding sites for 17,20β-P have been detected within 1 h incubation and the binding dissociated completely within 50 min at 4°C and was pH dependent (optimum pH 7.8). Scatchard analyses of specifically bound 17,20β-P showed the evidence of a single class of high affinity binding sites (KD = 22.9 nM), with limited capacity (Bmax = 2.1 pmol/g tissue) to the ovarian membrane of yellowtail undergoing FSM. Competition results revealed that ovarian membrane receptor was highly specific for 17,20β-P. There was no other steroid competed strongly with the binding sites of [3H]17,20β-P, except 17,20β-P itself. On the other hand, 17,20β-P did not bind to the membrane prepared from maturationally incompetent (MI) and ovulation (OV) stages of oocytes. As the time proceeded after the stimulation of HCG, binding activity increased significantly (0.389 ± 0.036 pmol/g tissue) in the ovarian membrane of maturationally competent (MC) oocytes by 12 h postinjection. The binding activity was further significant (0.868 ± 0.032 pmol/g tissue) at FSM by 24 h postinjection and reached its peak (0.920 ± 0.115 pmol/g tissue) temporarily at second stage of maturation (SSM) by 36 h postinjection and then sharply declined to the prestimulation levels during OV stage by 48 h postinjection. In addition to our previous findings, the present results indicate that 17,20β-P is the MIH in yellowtail..
15. Kohei Ohta, Sonoko Yamaguchi, Akihiko Yamaguchi, Koichi Okuzawa, Koichiro Gen, Hirohiko Kagawa, Michiya Matsuyama, Biosynthesis of estradiol-17β in the ovarian follicles of the red seabream Pagrus major during vitellogenesis, Fisheries Science, 10.1046/j.1444-2906.2002.00477.x, 68, 3, 680-687, 2002.07, The red seabream Pagrus major is a useful experimental fish for studying the endocrine control of oogenesis in teleosts. This study investigated the steroidogenic pathway for estradiol-17β (E2) biosynthesis in the ovarian follicles of red seabream. Intact follicles were isolated during vitellogenesis and incubated in vitro with different radiolabeled steroid precursors. When 17-hydroxyprogesterone (17-P), dehydroepiandrosterone (DHEA), or androstenedione (AD) were used as precursors, both testosterone (T) and estrone (E1) were synthesized by follicles, leading to estradiol-17β (E2) production. Serum steroid levels measured by enzyme-linked immunosorbent assay showed that T, E1, and E2 were present in the circulation at levels ranging from 1 ng/mL to 2 ng/mL throughout the day during the spawning season. In vitro conversion of E1 into E2, however, was 15.8-fold greater than T conversion into E2, suggesting that E2 is synthesized mainly via E1 rather than T. The results showed that E2 was synthesized from pregnenolone via 17-hydroxypregnenolone, DHEA, AD, and E1. Thus, the study demonstrated the complete steroidogenic E2 synthesis pathway in the ovarian follicles of red seabream, and revealed that E1 is the major precursor of E2..
16. Kohei Ohta, Sonoko Yamaguchi, Akihiko Yamaguchi, Koichiro Gen, Koichi Okuzawa, Hirohiko Kagawa, Michiya Matsuyama, Biosynthesis of steroids in ovarian follicles of red seabream, Pagrus major (Sparidae, Teleostei) during final oocyte maturation and the relative effectiveness of steroid metabolites for germinal vesicle breakdown in vitro, Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology, 10.1016/S1096-4959(02)00106-9, 133, 1, 45-54, 2002.09, The steroid synthesis pathway in the ovarian follicles of the red seabream during final oocyte maturation (FOM) was investigated by incubating intact follicles with different radioactively labeled steroid precursors. During FOM, the steroidogenic shift from estradiol-17β to 20β-hydroxylated progestin production occurred mainly due to a combination of inactivation of C17,20-lyase and activation of 20β-hydroxysteroid dehydrogenase. Of the steroids produced, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) exhibited the greatest effect on germinal vesicle breakdown (GVBD) in vitro. 17,20β-P was further converted to its 5β-reduced form, 17,20β-dihydroxy-5β-pregnan-3-one (17,20β-P-5β), which had lower GVBD activity, suggesting that 5β-reduction plays a role in the inactivation of the maturation-inducing ability of 17,20β-P. In contrast, no 5β-reduced metabolite of 20β-S was found. Serum levels of 17,20β-P and 20β-S, measured by ELISA, showed that circulating levels of both progestins increased during FOM, and 20β-S levels were approximately twice as high as 17,20β-P levels. This study clarified the complete steroidogenesis pathway during FOM in red seabream ovarian follicles and showed that two 20β-hydroxylated progestins, 17,20β-P and 20β-S, act as maturation-inducing hormones in this species. The catabolites of these two progestins and their physiological roles in reproduction are also discussed..
17. M. Anisur Rahman, Kohei Ohta, Hisashi Chuda, Akihiko Yamaguchi, Michiya Matsuyama, Steroid hormones and their synthetic pathways in the vitellogenic ovarian follicles of yellowtail, Seriola quinqueradiata, Journal of the Faculty of Agriculture, Kyushu University, 46, 2, 311-319, 2002.10, In the present study, we clarified the steroid hormones produced and their synthetic pathways, particularly focusing the estradiol-17β (E2) synthesis, in the vitellogenic ovarian follicles to provide information on the endocrine control of vitellogenesis in yellowtail, Seriola quinqueradiata. Intact vitellogenic ovarian follicles were isolated and incubated with radioactive [3H]pregnenolone and [14C]androstenedione and steroid metabolites were identified by thin layer chromatography (TLC) followed by recrystallization to constant specific activity. Results obtained clearly indicated that testosterone (T) is the substrate precursor of E2 synthesis. In the vitellogenic ovarian follicles, the steroid metabolites produced and major pathway followed were pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone, androstenedione (AD), T and E2. AD, T and E2 were also present in the serum of fish during vitellogenesis, and serum level of T was the highest (3.7ng/ml), followed by E2 (2.3ng/ml). Thus, this study demonstrated the complete steroidogenic pathway of E2 synthesis in the ovarian follicles of yellowtail, and revealed that T is the major precursor of E2..
18. J. K. Sundaray, Kohei Ohta, Akihiko Yamaguchi, K. Suzuki, Michiya Matsuyama, Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner, Fish Physiology and Biochemistry, 10.1023/B:FISH.0000030525.97946.5e, 28, 1-4, 193-195, 2003, The wrasse, Pseudolabrus sieboldi, is a diandric protogynous labrid fish. Spawning is performed by a terminal phase (TP) male and an initial phase (IP) female between 6:00 and 9:00 h daily during two-month-long spawning season. In the present study, to investigate the roles of steroid hormones in the diurnal spermatogenesis of the P. sieboldi TP male, all steroid hormones produced in the testis were identified and the synthetic pathways of these steroids were determined. Furthermore, the circulating levels of the major steroids produced were analyzed throughout a day at 3-hour intervals during spawning season. In the testis, 11-ketotestosterone (11-KT), estradiol-17β (E2), 17,20β-dihydoxy-4-pregnane-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesized as the major metabolites. In vitro steroid biosynthesis experiments showed similar results to the circulation profiles of the major steroids. This study is the first to clarify the complete steroidogenic pathways in the gonads of a diandric protogynous species throughout its life, when combined with the results of the steroidogenesis in the ovarian follicles. This is also the first report of a clear diurnal rhythm of the steroid production corresponding to the spermatogenic process in the testis of a male teleost..
19. Kohei Ohta, J. K. Sundaray, T. Okida, M. Sakai, T. Kitano, Akihiko Yamaguchi, T. Takeda, Michiya Matsuyama, Bi-directional sex change and its steroidogenesis in the wrasse, Pseudolabrus sieboldi, Fish Physiology and Biochemistry, 10.1023/B:FISH.0000030517.06738.e7, 28, 1-4, 173-174, 2003, The protogynous wrasse, Pseudolabrus sieboldi, is a good model for studying the physiological mechanism of sex change in teleosts. We established a way to induce sex change bidirectionally by controlling the social conditions in captivity. This is the first report of a reversed sex change in a promiscuous species. After identifying all the steroid hormones produced in the ovarian follicles and testis, and clarifying their synthetic pathways, we examined the function of the sex steroids in the sex change of P. sieboldi. We concluded that the activation of 17β-HSD-III is the first step in inducing morphological and functional change from an ovary to a testis..
20. M. A. Rahman, Kohei Ohta, Akihiko Yamaguchi, H. Chuda, T. Hirai, Michiya Matsuyama, Gonadotropins, gonadotropin receptors and their expressions during sexual maturation in yellowtail, a carangid fish, Fish Physiology and Biochemistry, 10.1023/B:FISH.0000030481.94719.a0, 28, 1-4, 81-83, 2003.12, To study the physiological roles of gonadotropins (GtHs) in the yellowtail, the cDNAs encoding each GtH subunit (GPHα, FSHβ and LHβ) and their receptors (FSHR and LHR) were isolated from the pituitary gland and gonads using the polymerase chain reaction (PCR). In addition, thyrotropin (TSH) and its receptor (TSHR) cDNAs, were isolated from the pituitary gland, ovary and testis. The changes in the mRNA levels of each subunit were determined at different stages of maturation. The isolated cDNAs of GPHα, FSHβ, LHβ and TSHβ were 662, 545, 595 and 879 bp long, respectively. The amino acid sequence identity of the yellowtail GPHα, FSHβ, LHβ and TSHβ subunits was 85-63, 68-33, 93-65 and 74-46%, respectively, as compared with other fish species. Northern blot analysis showed that GPHα and FSHβ were strongly expressed in pituitary at the early vitellogenic stage and during spermatogenesis, whereas LHβ was expressed significantly in the late vitellogenic stage, and in both spermatogenesis and spermiation. Full-length cDNAs encoding FSHR, LHR, and TSHR were obtained from the testes and ovaries. The FSHR, LHR and TSHR cDNA encoded a protein of 680, 702 and 778 amino acids, and showed the highest identity with tilapia FSHR (76%), tilapia LHR (84%) and striped bass TSHR (94%), respectively. Northern blot analyses indicated that all of these receptors are expressed differently at different stages in the ovaries and testes..
21. Michiya Matsuyama, Tetsuro Shiraishi, Jitendra K. Sundaray, Md Anisur Rahman, Kohei Ohta, Akihiko Yamaguchi, Steroidogenesis in ovarian follicles of chub mackerel, Scomber japonicus, Zoological Science, 10.2108/zsj.22.101, 22, 1, 101-110, 2005.01, We incubated different radiolabeled steroid precursors with intact chub mackerel ovarian follicles to clarify the synthetic pathways of steroid hormones during vitellogenesis and following final oocyte maturation (FOM). During vitellogenesis, estradiol-17β (E2) was synthesized from pregnenolone via 17-hydroxypregnenolone, 17-hydroxyprogesterone, androstenedione, and testosterone. The physiological significance of the intermediate metabolites of E2 in the ovarian follicles was examined by comparing follicular steroidogenesis between gonochoric and hermaphroditic fish species. After vitellogenesis, the steroidogenic pathway shifted from E2 to maturation-inducing hormone (MIH) production owing to the inactivation of 17,20-lyase and the activation of 20β-hydroxysteroid dehydrogenase. Of the new steroids produced during FOM, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was most effective at inducing germinal vesicle breakdown in vitro. Circulating levels of 17,20β-P increased specifically around the time of germinal vesicle migration, while another FOM-specific 20β-hydroxylated progestin, 17,20β,21-trihydroxy-4-pregnen-3-one, was present at consistently low levels during FOM. These results indicate that 17,20β-P is the MIH of chub mackerel..
22. Tetsuro Shiraishi, Kohei Ohta, Akihiko Yamaguchi, Mari Yoda, Hisashi Chuda, Michiya Matsuyama, Reproductive parameters of the chub mackerel Scomber japonicus estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity, Fisheries science, 10.1111/j.1444-2906.2005.00997.x, 71, 3, 531-542, 2005.06, Final oocyte maturation and ovulation of captive chub mackerel Scomber japonicus with fully yolk-accumulated oocytes were induced by a single injection of human chorionic gonadotropin. Reproductive parameters, including spawning frequency and batch fecundity, which are required to estimate spawning biomass in pelagic fish by the daily egg production method, were analyzed. Germinal vesicle migration (GVM) occurred at 18-24 h post-injection, and the hydration and ovulation of oocytes were completed at 30 and 36 h post-injection, respectively. The results of the maturation process suggest that fish with GVM-stage ovaries captured in the daytime from the field are capable of spawning on the night following their capture. The oocytes used in the oocyte size-frequency distribution method for batch fecundity estimates should be at late GVM and more advanced stages. The results of sequential artificial insemination showed that the quality of ovulated eggs held in the ovarian lumen rapidly deteriorated as time progressed after ovulation. This indicates that the fertilization window for the ovulated eggs of chub mackerel lasts only a few hours, and spawning behavior should be performed within a few hours after ovulation in the wild population..
23. Ohta, K, Sakai, M, Sundaray, JK, Kitano, T, Takeda, T, Yamaguchi, A, Matsuyama, M, Bidirectional Sex Change Induced by Sex Steroid Implantation in the Hermaphrodite Fish, Pseudolabrus sieboldi, JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL GENETICS AND PHYSIOLOGY, 10.1002/jez.1747, 317A, 9, 552-560, 2012.11.
24. Ohta, K, Yamamoto, M, Lin, Y, Hogg, N, Akiyama, H, Behringer, RR, Yamazaki, Y, Male Differentiation of Germ Cells Induced by Embryonic Age-Specific Sertoli Cells in Mice, BIOLOGY OF REPRODUCTION, 10.1095/biolreprod.111.095943, 86, 4, 2012.04.
25. Kitano, H, Irie, S, Ohta, K, Hirai, T, Yamaguchi, A, Matsuyama, M, Molecular cloning of two gonadotropin receptors and their distinct mRNA expression profiles in daily oogenesis of the wrasse Pseudolabrus sieboldi, GENERAL AND COMPARATIVE ENDOCRINOLOGY, 10.1016/j.ygcen.2011.03.012, 172, 2, 268-276, 2011.06.
26. Ohta, K, Lin, Y, Hogg, N, Yamamoto, M, Yamazaki, Y, Direct Effects of Retinoic Acid on Entry of Fetal Male Germ Cells into Meiosis in Mice, BIOLOGY OF REPRODUCTION, 10.1095/biolreprod.110.085787, 83, 6, 1056-1063, 2010.12.
27. Ohta, K, Mine, T, Yamaguchi, A, Matsuyama, M, Sexually Dimorphic Expression of Pituitary Glycoprotein Hormones in a Sex-Changing Fish (Pseudolabrus sieboldi), JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL GENETICS AND PHYSIOLOGY, 10.1002/jez.485, 309A, 9, 534-541, 2008.11.
28. Ohta, K, Hirano, M, Mine, T, Mizutani, H, Yamaguchi, A, Matsuyama, M, Body color change and serum steroid hormone levels throughout the process of sex change in the adult wrasse, Pseudolabrus sieboldi, MARINE BIOLOGY, 10.1007/s00227-007-0856-0, 153, 5, 843-852, 2008.02.
29. Kurokawa, H, Saito, D, Nakamura, S, Katoh-Fukui, Y, Ohta, K, Baba, T, Morohashi, K-I, Tanaka, M, Germ cells are essential for sexual dimorphism in the medaka gonad, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 10.1073/pnas.0609932104, 104, 43, 16958-16963, 2007.10.
30. Ohta, K, Sundaray, JK, Kitano, T, Shibara, Y, Matsuda, M, Yamaguchi, A, Matsuyama, M, Nagahama, Y, Involvement of 17 beta-hydroxysteroid dehydrogenase in the sex change of a protogynous wrasse, Pseudolabrus sieboldi, JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-COMPARATIVE EXPERIMENTAL BIOLOGY, 305A, 2, 164-164, 2006.02.
31. Shiraishi, T, Ohta, K, Akihiko Yamaguchi, Yoda, M, Chuda, H, Michiya Matsuyama, Reproductive parameters of the chub mackerel Scomber japonicus estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity, FISHERIES SCIENCE, 71, 3, 531-542, 2005.06.
32. Sundaray, JK, Ohta, K, Yamaguchi, A, Kitano, T, Matsuyama, M, Isolation, cloning, sequencing of brain type aromatase and its expression in male and female Wrasse, Pseudolabrus sieboldi, FISH PHYSIOLOGY AND BIOCHEMISTRY, 10.1007/s10695-006-0015-4, 31, 2-3, 137-141, 2005.04.
33. Michiya Matsuyama, Shiraishi, T, Sundaray, JK, Rahman, MA, Ohta, K, Akihiko Yamaguchi, Steroidogenesis in ovarian follicles of chub mackerel, Scomber japonicus, ZOOLOGICAL SCIENCE, 22, 1, 101-110, 2005.01.
34. Sundaray, JK, Ohta, K, Akihiko Yamaguchi, Suzuki, K, Michiya Matsuyama, Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner, FISH PHYSIOLOGY AND BIOCHEMISTRY, 28, 1-4, 193-195, 2003.03.
35. Ohta, K, Sundaray, JK, Okida, T, Sakai, M, Kitano, T, Akihiko Yamaguchi, Takeda, T, Michiya Matsuyama, Bi-directional sex change and its steroidogenesis in the wrasse, Pseudolabrus sieboldi, FISH PHYSIOLOGY AND BIOCHEMISTRY, 28, 1-4, 173-174, 2003.03.
36. Rahman, MA, Ohta, K, Yamaguchi, A, Chuda, H, Hirai, T, Matsuyama, M, Gonadotropins, gonadotropin receptors and their expressions during sexual maturation in yellowtail, a carangid fish, FISH PHYSIOLOGY AND BIOCHEMISTRY, 28, 1-4, 81-83, 2003.03.
37. Ohta, K, Rahman, MA, Chuda, H, Yoshikuni, M, Nagahama, Y, Matsuyama, M, Maturation-inducing hormone and its membrane receptor in gonads of Japanese yellowtail, Seriola quinqueradiata., FISHERIES SCIENCE, 68, 686-689, 2002.10.
38. Ohta, K, Yamaguchi, S, Yamaguchi, A, Gen, K, Okuzawa, K, Kagawa, H, Michiya Matsuyama, Biosynthesis of steroids in ovarian follicles of red seabream, Pagrus major (Sparidae, Teleostei) during final oocyte maturation and the relative effectiveness of steroid metabolites for germinal vesicle breakdown in vitro, COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY B-BIOCHEMISTRY & MOLECULAR BIOLOGY, 133, 1, 45-54, 2002.09.
39. Rahman, MA, Ohta, K, Yoshikuni, M, Nagahama, Y, Chuda, H, Matsuyama, M, Characterization of ovarian membrane receptor for 17,20 beta-dihydroxy-4-pregnen-3-one, a maturation-inducing hormone in yellowtail, Seriola quinqueradiata, GENERAL AND COMPARATIVE ENDOCRINOLOGY, 127, 1, 71-79, 2002.06.
40. Ohta, K, Yamaguchi, S, Yamaguchi, A, Okuzawa, K, Gen, K, Kagawa, H, Matsuyama, M, Biosynthesis of estradiol-17 beta in the ovarian follicles of the red seabream Pagrus major during vitellogenesis, FISHERIES SCIENCE, 68, 3, 680-687, 2002.06.
41. Ohta, K, Matsuyama, M, Steroidogenic pathways to 17,20 beta-dihydroxy-4-pregnen-3-one and 17,20 beta,21-trihydroxy-4-pregnen-3-one in the ovarian follicles of the bambooleaf wrasse Pseudolabrus sieboldi, FISHERIES SCIENCE, 68, 1, 41-50, 2002.02.
42. Ohta, K, Mine, T, Yamaguchi, A, Matsuyama, M, Steroidogenic pathway to estradiol-17 beta synthesis in the ovarian follicles of the protogynous wrasse, Pseudolabrus sieboldi, ZOOLOGICAL SCIENCE, 18, 7, 937-945, 2001.09.
43. Rahman, MA, Ohta, K, Chuda, H, Yamaguchi, A, Matsuyama, M, Steroid hormones and their synthetic pathways in the vitellogenic ovarian follicles of yellowtail, Seriola quinqueradiata, JOURNAL OF THE FACULTY OF AGRICULTURE KYUSHU UNIVERSITY, 46, 2, 311-319, 2002.02.
44. M. A. Rahman, Kohei Ohta, H. Chuda, S. Nakano, K. Maruyama, Michiya Matsuyama, Gonadotropin-induced steroidogenic shift towards maturation-inducing hormone in Japanese yellowtail during final oocyte maturation, Journal of Fish Biology, 10.1006/jfbi.2000.1471, 58, 2, 462-474, 2001.06, Intact ovarian follicles, obtained from untreated and human chorionic gonadotropin (HCG) treated Japanese yellowtail Seriola quinqueradiata during different maturational stages, were incubated with radioactive [
3
H]pregnenolone, [
3
H]17-hydroxyprogesterone or [
14
C] androstenedione and steroid metabolites identified by thin layer chromatography (TLC) followed by recrystallization to constant specific activity. In untreated late vitellogenic (0 h) follicles, androstenedione was the major product with smaller amounts of testosterone and oestradiol-17β. In post-vitellogenic (12 h post-injection) intact follicles, androstenedione predominated, and although testosterone and oestradiol-17β were not produced, there were small amounts of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,21-dihydroxy-4-pregnene-3,20-dione (11-deoxycortisol). In HCG-treated fish, a steroidogenic shift resulted in the disappearance of testosterone and oestradiol-17β coinciding with the appearance of 17,20β-P. During early and late final oocyte maturation FOM (24 and 36 h post-injection), there was a five- to seven-fold increase in the production of 17,20β-P, whereas production of 11-deoxycortisol remained almost the same. During FOM, in addition to 17,20β-P, its 5β-reduced metabolite, 17,20β-dihydroxy-5β-pregnan-3-one (5β-17,20β-P) was synthesized, suggesting a decrease in maturation-inducing 17,20β-P activity. 17,20β,21-Trihydroxy-4-pregnen-3-one (20β-S) was not synthesized by ovarian fragments in Japanese yellowtail at any maturational stage. The metabolites identified on TLC during FOM were tested to evaluate their maturation-inducing activity in an in vitro bioassay. Of the steroids tested, 17,20β-P was the most effective inducer of germinal vesicle breakdown (GVBD), followed by 5β-17,20β-P. Timely synthesis of 17,20β-P immediately prior to and during FOM as well as its great potency in inducing GVBD in vitro supports the evidence for a physiological role of 17,20β-P as a maturation-inducing hormone in Japanese yellowtail..
45. Kohei Ohta, Takayuki Mine, Akihiko Yamaguchi, Michiya Matsuyama, Steroidogenic pathway to estradiol-17β synthesis in the ovarian follicles of the protogynous wrasse, Pseudolabrus sieboldi, Zoological Science, 10.2108/zsj.18.937, 18, 7, 937-945, 2001.09, The bambooleaf wrasse, Pseudolabrus sieboldi, is a diandric protogynous fish with a diurnal rhythm of ovarian development, and females spawn daily during the spawning season. This study investigated the steroidogenic pathway for estradiol-17β (E2) biosynthesis in vitellogenic ovarian follicles of the bambooleaf wrasse. We incubated follicles in vitro with radioactively labeled steroid precursors, and measured serum steroid levels using microtiter plate enzyme-linked immunosorbent assays (ELISAs). ELISAs for estrone (E1) and testosterone (T) were developed. The experiments showed that E2 was synthesized from pregnenolone via 17-hydroxypregnenolone, dehydroepiandrosterone, androstenedione, and E1. T was not produced from any radiolabeled precursors, and exogenous T was not converted to E2. During the spawning season, serum levels of E2 and E1 showed similar patterns, with a diurnal rhythm of high levels at 03:00 hr associated with active ovarian vitellogenic follicles. In contrast, serum T levels were constant and relatively low compared to levels of E2 and E1. These results indicate that E2 is synthesized via E1, rather than T, in the ovarian follicles, and suggest that T detected in the blood is likely derived from extra-follicular tissues..
46. Kohei Ohta, Michiya Matsuyama, Steroidogenic pathways to 17,20β-dihydroxy-4-pregnen-3-one and 17,20β,21-trihydroxy-4-pregnen-3-one in the ovarian follicles of the bambooleaf wrasse Pseudolabrus sieboldi, Fisheries Science, 10.1046/j.1444-2906.2002.00387.x, 68, 1, 41-50, 2002, Intact follicles of the bambooleaf wrasse were incubated with different radioactively labeled steroid precursors during final oocyte maturation (FOM), and the maturation-inducing hormone (MIH) of this species was examined to compare the activities of the steroid metabolites produced on germinal vesicle breakdown (GVBD) in vitro. Of the metabolites obtained by thin layer chromatography, two steroids, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S), both had the greatest effect on GVBD in vitro. During FOM, a shift in steroidogenic enzymes, a decrease in C17,20-lyase activity, and an increase in 20β-HSD activity were found. In addition to this shift, continuous high 21-hydroxylase activity throughout all the oocyte developmental stages was observed, and, in all likelihood, this 21-hydroxylase activity enables ovarian follicles to synthesize enough 17,21-P. Consequently, activated 20β-hydroxysteroid dehydrogenase converted 17-P and 17,21-P to 17,20β-P and 20β-S, respectively, during FOM. Thus, the present study not only provides evidence on the physiological role of 17,20β-P and 20β-S as MIH in the bambooleaf wrasse, but also details the enzymatic kinetics of 17,20β-P and 20β-S biosynthesis..
47. Rahman, MA, Ohta, K, Chuda, H, Nakano, S, Maruyama, K, Matsuyama, M, Gonadotropin-induced steroidogenic shift towards maturation-inducing hormone in Japanese yellowtail during final oocyte maturation, JOURNAL OF FISH BIOLOGY, 58, 2, 462-474, 2001.02.
48. Matsuyama, M, Ohta, K, Morita, S, Hoque, MM, Kagawa, H, Kambegawa, A, Circulating levels and in vitro producton of two maturation-inducing hormones in teleost: 17α,20β-dihydroxy-4-pregnen-3-one and 17α,20β,21-tritydroxy-4-pregnen-3-one, in adaily spawning wrasse, Pseudolabrus japonicus., Fish Physiology and Biochemistry, 19, 1-4, 1-11, 1998.06.
49. Michiya Matsuyama, Sumito Morita, Nobuhide Hamaji, Masaaki Kashiwagi, Kohei Ohta, Yoshitaka Nagahama, Diurnal spermatogenesis and spawning in the secondary male of a protogynous wrasse, Pseudolabrus japonicus (Teleostei, Labridae), Zoological Science, 10.2108/zsj.14.1001, 14, 6, 1001-1008, 1997, The bambooleaf wrasse, Pseudolabrus japonicus, exhibits diandric protogyny, and the secondary male performs pair spawning with a female who enters his territory. We examined diurnal spermatogenesis and spawning in the secondary male of a protogynous wrasse. In captivity, a single secondary male spawned daily over one month between 06:00 and 09:00 from October to November. Number of B-type spermatogonia and spermatocytes showed the lowest level at 00:00, increased gradually thereafter, peaked at 15:00, and decreased rapidly from 21:00 to 00:00. Spermatid number did not change significantly throughout the day. The number of spermatozoa increased gradually from 18:00, reached a maximum at 06:00, just prior to spawning, and thereafter decreased markedly at 09:00, after spawning. These results clearly showed that spermatogonial proliferation and meiosis occurred between 00:00 and 15:00, and spermiation occurred between 18:00 and 06:00. Thus, the secondary male of bambooleaf wrasse exhibits a diurnal rhythm of spermatogenesis and spermiation..
50. Michiya Matsuyama, Kohei Ohta, S. Morita, M. M. Hoque, H. Kagawa, A. Kambegawa, Circulating levels and in vitro production of two maturation-inducing hormones in teleost
17α,20β-dihydroxy-4-pregnen-3-one and 17α,20β,21-trihydroxy-4-pregnen-3-one, in a daily spawning wrasse, Pseudolabrus japonicus, Fish Physiology and Biochemistry, 10.1023/A:1007761729290, 19, 1, 1-11, 1998.01, The female bambooleaf wrasse, Pseudolabrus japonicus, spawns daily during the spawning season, and exhibits a diurnal rhythm of ovarian development. In the present study, we have investigated: (1) circulating levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17α,20β,21-trihydroxy-4-pregnen-3-one (20β-S) in females sampled at different times of the day during spawning season in captivity, and (2) in vitro production of 17,20β-P and 20β-S by follicle-enclosed oocytes at seven different developmental stages. In addition, we developed a microtiter plate enzyme-linked immunosorbent assay (ELISA) for 17,20β-P. Serum levels of 17,20β-P and 20β-S showed similar diurnal changes; substantial increases in these levels occurred around the time of germinal vesicle breakdown (GVBD). In vitro experiments showed that massive production of 17,20β-P and 20β-S occurred in follicles collected just before or during GVBD. Further, acute decreases in 17,20β-P and 20β-S production were found in the ovarian follicles just prior to ovulation, suggesting inactivation of the maturation-inducing hormone (MIH). These results, taken together with our previous data on the occurrence of GVBD in vitro, suggest a role for both 17,20β-P and 20β-S as MIHs in the bambooleaf wrasse..
51. Matsuyama, M, Morita, S, Hamaji, N, Kashiwagi, M, Ohta, K, Nagahama, Y, Diurnal spermatogenesis and spawning in the secondary male of a protogynous wrasse, Pseudolabrus japonicus (Teleostei, Labridae), ZOOLOGICAL SCIENCE, 14, 6, 1001-1008, 1997.12.