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Akihiko Yamaguchi Last modified date:2024.03.26

Assistant Professor / Marine Bioresources
Department of Bioresource Sciences
Faculty of Agriculture

Graduate School
Undergraduate School

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Fishes are interesting group of organisms in which to analyze sex determination and gonad development because they have various type of sexuality. Recently, the medaka Y-specific sex determination gene, DMY which is a duplicated copy of autosomal DMRT1 was identified. In other fishes, however, no molecular information exists about the mode of sex determination, sex chromosomes or the process of gonad differentiation. Our goal is determination of the common molecular mechanism of gonad development of useful marine fishes at the molecular and cellular level, then bring it back to the our life, enviroment and society.
Please step into the world of the marine reproductive biology with us. .
Academic Degree
Country of degree conferring institution (Overseas)
Field of Specialization
Reproductive Biology, Molecular Cell Biology
Total Priod of education and research career in the foreign country
Outline Activities
Fishes are interesting group of organisms in which to analyze sex determination and gonad development because they have various type of sexuality. Recently, the medaka Y-specific sex determination gene, DMY which is a duplicated copy of autosomal DMRT1 was identified. In other fishes, however, no information exists about the mode of sex determination, sex chromosomes or the process of gonad differentiation. We study molecular mechanism of these process using kinds of fishes(goldfish, pufferfish, zebrafish, so on). Recently, we try to analyze the germ cell differntiation during early larvae of Japanese pufferfish, Takifugu rubripes which has the most compact genomes of all vertebrates and used as a good model for comparative genome analysis. At present, we have been investigating the transcription factors that are necesary for differentiation of germ cells. Aromatase is an important steroidogenic enzyme converts androgen to estroge.Brain type aromatase (CYP19B) has a unique characteristics because fish brain 100-1000 fold more proteins and activity than mammals. We have been studying the role of estrogen in fish brain as well as gonads and other somatic organs.
Research Interests
  • The molecular study of gonadal sexual differentiation, development, maturation and environmental responsibility of Torafugu (Takifugu rubripes)
    The molecular study of pituitary hormone synthesis and secretion using 3D spheroid culture system
    keyword : Torafugu, gonadal sexual differntiation, transcription factor, steroidgenic enzyme, ER, GTH, Rhodopsin, opsin.pituitary, spheroid
    2000.10We analyze transcription factors, steroidogenic enzymes that works for sex-differentiation and development of the gonads. Recently, we target on the nuclear matrix that may be a key structure to understand molecular mechanism of gene expression system in germ cells..
  • Molecular analysis of nuclear (germinal vesicle) structure and function in fish oocytes
    keyword : lamin,protein kinase,MPF,cdc2,SR protein, oocyte maturation,goldfish
Academic Activities
1. @Akihiko Yamaguchi, Evaluation of fish pituitary spheroids to study annual endocrine reproductive control, General and Comparative Endocrinology 351 (2024) 114481 ,, 351 , 2024.03, [URL], The pituitary gland is a small endocrine gland located below the hypothalamus. This gland releases several important hormones and controls the function of many other endocrine system glands to release hormones. Fish pituitary hormonal cells are controlled by neuroendocrine and sex steroid feedback. To study the complex pituitary function in vivo, we established an in vitro pituitary spheroid assay and evaluated its suitability for monitoring the annual reproductive physiological conditions in Takifugu rubripes, also known as torafugu, is one of the most economically important species distributed in the northwestern part of the Pacific Ocean, in the western part of the East China Sea, and in more northern areas near Hokkaido, Japan. Fish pituitary spheroids can be easily constructed in liquid or solid plates. The culture medium (L-15) made the aggregation faster than MEM (Hank’s). A Rho-kinase inhibitor (Y-27632, 10 μM) and/or fish serum (2.5 %) also promoted spheroid formation. Laser confocal microscopy analysis of spheroids cultured with annual serum of both sexes revealed that luteinizing hormone (LH) synthesis has the highest peak in the final maturation stage (3 years old, May) in accordance with the highest serum sex steroid levels; in contrast, follicle stimulating hormone (FSH) synthesis has no correlation with the dose of serum or nutrients. Similarly, 3D cell propagation assays using female serum showed that total pituitary cells displayed the highest proliferation at puberty onset (2 years old, October) before half a year of the spawning season. These results indicate that pituitary spheroids are useful in vitro models for monitoring the reproductive physiological status of fish in vivo and may be applicable to the in vitro screening of environmental chemicals and bioactive compounds affecting reproductive efficiency in aquaculture..
2. Akihiko Yamaguchi, Tomoko Tsunematsu, Yoshihiro Motojima, Kanako Toriyama, Asami Horinouchi, Yukari Ishii, Hanezu Murata, Sota Yoshikawa, Mitsuo Nyuji, Akio Shimizu, Pituitary luteinizing hormone synthesis starts in aromatase (cyp19a1b)‑positive cells expressing esr1 and esr2b at the onset of puberty in Takifugu rubripes (fugu), Cell and Tissue Research, 10.1007/s00441-022-03629-6, 2022.05, Unlike mammals, teleost fsh have high aromatase activity (AA) in the pituitary. However, the cells responsible for oestradiol synthesis and the local physiological roles of this hormone remain unclear. Hence, we investigated the efects of age and development on steroidogenic activity, mRNA expression, and cyp19a1b localization in the pituitary gland of the Japanese puferfsh Takifugu rubripes. Under aquaculture conditions, AA was highest after puberty, and the mRNA expression levels of cyp19a1b and the oestrogen receptors esr1 and 2b and the level of serum testosterone (T) were signifcantly increased after puberty compared with the other developmental stages in male and female puferfsh. Immunohistochemistry using multiple antibodies and in situ hybridization analysis revealed that Cyp19a1b colocalizes with luteinizing hormone (LH) in pituitary cells. Furthermore, Esr1 was localized in the nuclei of all hormone-producing cells, whereas Esr2b was localized only in the nuclei of Cyp19- and LH-positive cells. The administration of an aromatizable androgen (T) or oestrogen (E2) to reproductively inactive females induced LH synthesis in vivo. We prepared spheroids from pituitary cells to investigate the role of local E2 in LH synthesis in vitro. Immunohistochemical analysis of spheroids showed that T-induced LH synthesis could be blocked by an aromatase inhibitor and/or an ER antagonist but not an AR antagonist. Taken together, these fndings suggest that LH synthesis is initiated in cyp19a1b-, esr1-, and esr2b-expressing cells at the onset of puberty under the control of steroidal feedback, and both feedback and local oestrogen may be involved in controlling LH synthesis in these cells..
3. @Akihiko Yamaguchi, #Miho Iwatani, #Mariko Ogawa, #Hajime Kitano,@Michiya Matsuyama, In vitro characterization of the RS motif in N-terminal head domain of goldfish germinal vesicle lamin B3 necessary for phosphorylation of the p34cdc2 target serine by SRPK1, FEBS Open Bio, 10.1016/j.fob.2013.03.003, 3, 165-176, 2013.03, The nuclear envelopes surrounding the oocyte germinal vesicles of lower vertebrates (fish and frog)
are supported by the lamina, which consists of the protein lamin B3 encoded by a gene found also in
birds but lost in the lineage leading to mammals. Like other members of the lamin family, goldfish
lamin B3 (gfLB3) contains two putative consensus phosphoacceptor p34cdc2 sites (Ser-28 and Ser-398)
for the M-phase kinase to regulate lamin polymerization on the N- and C-terminal regions flanking a
central rod domain. Partial phosphorylation of gfLB3 occurs on Ser-28 in the N-terminal head domain
in immature oocytes prior to germinal vesicle breakdown, which suggests continual rearrangement of
lamins by a novel lamin kinase in fish oocytes. We applied the expression-screening method to isolate
lamin kinases by using phosphorylation site Ser-28-specific monoclonal antibody and a vector encoding
substrate peptides from a goldfish ovarian cDNA library. As a result, SRPK1was screened as a prominent
lamin kinase candidate. The gfLB3 has a short stretch of the RS repeats (9-SRASTVRSSRRS-20) upstream
of the Ser-28, within the N-terminal head. This stretch of repeats is conserved among fish lamin B3 but
is not found in other lamins. In vitro phosphorylation studies and GST-pull down assay revealed that
SRPK1 bound to the region of sequential RS repeats (9–20) with affinity and recruited serine into the
active site by a grab-and-pull manner. These results indicate SRPK1may phosphorylate the p34cdc2 site
in the N-terminal head of GV-lamin B3 at the RS motifs,which have the general property of aggregation..
4. Yamaguchi, A., Katsu,Y., Matsuyama, M., Yoshikuni, M., Nagahama,Y., Phosphorylation of the p34cdc2 target site on goldfish germinal vesicle lamin B3 before oocyte maturation, European Journal of Cell Biology, 85, 501-517, 2006.06.
5. Yamaguchi, A., Lee,K-H., Fujimoto, H., kadomura,K., Yasumoto,S.,Matsuyama, M., Expression of DMRT gene and its roles in early gonadal development of Japanese pufferfish Takifugu rubripes, Comarative Biochemistry and Physiology Part D: Genomics and Proteomics, 1, 59-68, 2006.01.
6. Yamaguchi, A. and Nagahama, Y., Somatic lamins in germinal vesicles of goldfish (Carassius auratus) oocytes., Cell Struc. Func., 26, 693‐703., 2001.01.
7. Yamaguchi, A., Yamashita, M., Yoshikuni, M. and Nagahama, Y., Identification and molecular cloning of germinal vesicle lamin B3 in goldfish (Carassius autratus) oocytes., Eur. J. Biochem., 268, 932-939., 2001.01.
8. Yamaguchi, A., Yamashita, M., Yoshikuni, M., Hotta,Y., Nurse, P. and Nagahama, Y., Involvement in meiotic prophase of H1 kinase and p34cdc2 homologues in lily (Lilium longiflorum) microsporocytes., Develop. Growth Differ., 33, 625-632., 1991.01.
Membership in Academic Society
  • Japanease Association for Animal Cell Technology
  • The Japan Society for Pituitary Research
  • Zoological Society of Japan
Educational Activities
Basic Biology Experiment
Laboratory in Fisheries Biology I
Laboratory in Fisheries Biology II
Molecular Biology
Animal and Marine Life Science (G30 English program)