Regulatory mechanisms underlying germ granule dynamics by newly identified maternal factors

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H02489
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 44020:Developmental biology-related
• Research Institution: Kumamoto University
• Principal Investigator: Nakamura Akira 熊本大学, 発生医学研究所, 教授 (90323245)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 生殖細胞 / 生殖顆粒 / 相分離 / 母性RNA / トランスポゾン / piRNA

Outline of Final Research Achievements

Germ cells give rise to gametes and transmit genetic information to offspring. Drosophila germ cell formation relies on the germ plasm, which is assembled into condensates with maternal RNAs and proteins. Many germ plasm proteins including Aubergine (Aub), also localize around nurse cell nuclei and form condensates, called nuage, which is the site for piRNA production and Aub-dependent cleavage of transposons. How the functions and assemblies of the nuage and germ plasm are coordinated remains elusive.
We have identified a novel maternal factor involved in the germ plasm assembly, named tiny pole plasm (tpp). In tpp- ovaries, the posterior localization of Aub was reduced. Tpp colocalized with Aub in the nuage, but not in the germ plasm. In tpp- ovaries, the amount of Aub-bound piRNAs was reduced, without severe derepression of transposons. These results suggest that differential piRNA abundance is required for transposon silencing and germ plasm assembly in the Drosophila ovary.

Free Research Field

発生生物学

Academic Significance and Societal Importance of the Research Achievements

トランスポゾンはゲノム情報に損傷を与える。一方、生物進化の原動力の一つでもあると考えられている。本研究では、ショウジョウバエをモデルに、トランスポゾンの分解を行うpiRNAが生殖細胞形成にも重要であり、生殖細胞形成に必要なpiRNA量の閾値がトランスポゾン抑制の必要量よりも高いことを明らかにした。ショウジョウバエではpiRNAが次世代の生殖細胞に引継がれトランスポゾン抑制に貢献する。卵巣内でトランスポゾン抑制に必要な量よりも過剰なpiRNAを産生することで、次世代に十分な多様性を持ったpiRNAの伝搬を保証していると予想された。このような知見は今まで提唱されておらず、学術的意義が高い。