Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

PIWI-interacting RNAs (piRNAs) protect germline genomes and maintain fertility by repressing transposons. Daedalus and Gasz act together as a mitochondrial scaffold for Armitage, a necessary factor for Zucchini-dependent piRNA processing. However, the mechanism underlying this function remains unclear. Here, we find that the roles of Daedalus and Gasz in this process are distinct, although both are necessary: Daedalus physically interacts with Armitage, whereas Gasz supports Daedalus to maintain its function. Daedalus binds to Armitage through two distinct regions, an extended coiled coil identified in this study and a sterile α motif (SAM). The former tethers Armitage to mitochondria, while the latter controls Zucchini endonucleolysis to define the length of piRNAs in an exonuclease-independent manner. piRNAs produced in the absence of the Daedalus SAM do not exhibit full transposon silencing functionality. Daedalus is Dipteran specific. Unlike Drosophila and mosquitoes, other species, such as mice, rely on exonucleases after Zucchini processing to specify the length of piRNAs.

DOI： 10.1016/j.celrep.2024.114923

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Publishing type：Research paper (scientific journal)   Publisher：Biophysical Society of Japan  

Phosphorylation regulates protein function by modulating stereospecific interactions between protein-protein or enzyme-ligand. On the other hand, many bioinformatics studies have demonstrated that phosphorylation preferably occurs in intrinsically disordered regions (IDRs), which do not have any secondary and tertiary structures. Although studies have demonstrated that phosphorylation changes the phase behavior of IDRs, the mechanism, which is distinct from the “stereospecific” effect, had not been elucidated. Here, we describe how phosphorylation in IDRs regulates the protein function by modulating phase behavior. Mitotic phosphorylation in the IDRs of Ki-67 and NPM1 promotes or suppresses liquid-liquid phase separation, respectively, by altering the “charge blockiness” along the polypeptide chain. The phosphorylation-mediated regulation of liquid-liquid phase separation by enhancing or suppressing "charge blockiness," rather than by modulating stereospecific interactions, may provide one of the general mechanisms of protein regulation by posttranslational modifications and the role of multiple phosphorylations.

DOI： 10.2142/biophysico.bppb-v21.0012

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Bombyx Vasa (BmVasa) assembles non-membranous organelle, nuage or Vasa bodies, in germ cells, known as the center for Siwi-dependent transposon silencing and concomitant Ago3-piRISC biogenesis. However, details of the body assembly remain unclear. Here, we show that the N-terminal intrinsically disordered region (N-IDR) and RNA helicase domain of BmVasa are responsible for self-association and RNA binding, respectively, but N-IDR is also required for full RNA-binding activity. Both domains are essential for Vasa body assembly in vivo and droplet formation in vitro via phase separation. FAST-iCLIP reveals that BmVasa preferentially binds transposon mRNAs. Loss of Siwi function derepresses transposons but has marginal effects on BmVasa-RNA binding. This study shows that BmVasa assembles nuage by phase separation via its ability to self-associate and bind newly exported transposon mRNAs. This unique property of BmVasa allows transposon mRNAs to be sequestered and enriched in nuage, resulting in effective Siwi-dependent transposon repression and Ago3-piRISC biogenesis.

DOI： 10.1038/s41467-023-37634-2

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Other Link： https://www.nature.com/articles/s41467-023-37634-2

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Cell Biology  

Dynamic morphological changes of intracellular organelles are often regulated by protein phosphorylation or dephosphorylation1-6. Phosphorylation modulates stereospecific interactions among structured proteins, but how it controls molecular interactions among unstructured proteins and regulates their macroscopic behaviours remains unknown. Here we determined the cell cycle-specific behaviour of Ki-67, which localizes to the nucleoli during interphase and relocates to the chromosome periphery during mitosis. Mitotic hyperphosphorylation of disordered repeat domains of Ki-67 generates alternating charge blocks in these domains and increases their propensity for liquid-liquid phase separation (LLPS). A phosphomimetic sequence and the sequences with enhanced charge blockiness underwent strong LLPS in vitro and induced chromosome periphery formation in vivo. Conversely, mitotic hyperphosphorylation of NPM1 diminished a charge block and suppressed LLPS, resulting in nucleolar dissolution. Cell cycle-specific phase separation can be modulated via phosphorylation by enhancing or reducing the charge blockiness of disordered regions, rather than by attaching phosphate groups to specific sites.

DOI： 10.1038/s41556-022-00903-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.15252/embj.202010513

Language：English   Publisher：(一社)日本生物物理学会