Ahmad Adam, Bogoch Yoel, Shvaizer Gal, Guler Noga, Levy Karine, Elkouby Yaniv M
Department of Developmental Biology and Cancer Research, The Hebrew University of Jerusalem Faculty of Medicine, Ein- Kerem Campus, Jerusalem, Israel.
Institute for Medical Research - Israel-Canada (IMRIC), Ein- Kerem Campus, Jerusalem, Israel.
PLoS Genet. 2025 Jan 13;21(1):e1010868. doi: 10.1371/journal.pgen.1010868. eCollection 2025 Jan.
Germ cells are essential for fertility, embryogenesis, and reproduction. Germline development requires distinct types of germ granules, which contains RNA-protein (RNP) complexes, including germ plasm in embryos, piRNA granules in gonadal germ cells, and the Balbiani body (Bb) in oocytes. However, the regulation of RNP assemblies in zebrafish germline development are still poorly understood. Asz1 is a piRNA protein in Drosophila and mice. Zebrafish Asz1 localizes to both piRNA and Bb granules, with yet unknown functions. Here, we hypothesized that Asz1 functions in germ granules and germline development in zebrafish. We generated asz1 mutant fish to determine the roles of Asz1 in germ cell development. We show that Asz1 is dispensable for somatic development, but essential for germ cell and gonad development. asz1-/- fish developed exclusively as sterile males with severely underdeveloped testes that lacked germ cells. In asz1 mutant juvenile gonads, germ cells undergo extensive apoptosis, demonstrating that Asz1 is essential for germ cell survival. Mechanistically, we provide evidence to conclude that zygotic Asz1 is not required for primordial germ cell specification or migration to the gonad, but is essential during post-embryonic gonad development, likely by suppressing the expression of germline transposons. Increased transposon expression and mis-organized piRNA granules in asz1 mutants, argue that zebrafish Asz1 functions in the piRNA pathway. We generated asz1;tp53 fish to partially rescue ovarian development, revealing that Asz1 is also essential for oogenesis. We further showed that in contrast with piRNA granules, Asz1 is dispensable for Bb granule formation, as shown by normal Bb localization of Buc and dazl. By uncovering Asz1 as an essential regulator of germ cell survival and gonadogenesis in zebrafish, and determining its differential necessity in distinct germ granule types, our work advances our understanding of the developmental genetics of reproduction and fertility, as well as of germ granule biology.
生殖细胞对于生育、胚胎发生和繁殖至关重要。生殖系发育需要不同类型的生殖颗粒，这些颗粒包含RNA-蛋白质（RNP）复合物，包括胚胎中的生殖质、性腺生殖细胞中的piRNA颗粒以及卵母细胞中的巴尔比亚尼体（Bb）。然而，斑马鱼生殖系发育过程中RNP组装的调控仍知之甚少。Asz1是果蝇和小鼠中的一种piRNA蛋白。斑马鱼Asz1定位于piRNA和Bb颗粒，但其功能尚不清楚。在这里，我们假设Asz1在斑马鱼的生殖颗粒和生殖系发育中发挥作用。我们生成了asz1突变鱼，以确定Asz1在生殖细胞发育中的作用。我们发现Asz1对于体细胞发育是可有可无的，但对于生殖细胞和性腺发育是必不可少的。asz1-/-鱼仅发育为不育雄性，睾丸严重发育不全，缺乏生殖细胞。在asz1突变的幼年性腺中，生殖细胞经历广泛的凋亡，表明Asz1对于生殖细胞存活至关重要。从机制上讲，我们提供的证据表明，合子型Asz1对于原始生殖细胞的特化或迁移到性腺不是必需的，但在胚胎后期性腺发育过程中是必不可少的，可能是通过抑制生殖系转座子的表达。asz1突变体中转座子表达增加和piRNA颗粒组织紊乱，表明斑马鱼Asz1在piRNA途径中发挥作用。我们生成了asz1;tp53鱼以部分挽救卵巢发育，揭示Asz1对于卵子发生也是必不可少的。我们进一步表明，与piRNA颗粒不同，Asz1对于Bb颗粒形成是可有可无的，如Buc和dazl在Bb中的正常定位所示。通过揭示Asz1是斑马鱼生殖细胞存活和性腺发生的重要调节因子，并确定其在不同生殖颗粒类型中的不同必要性，我们的工作推进了我们对生殖和生育发育遗传学以及生殖颗粒生物学的理解。
