Key Laboratory of Evolution & Marine Biodiversity (Ministry of Education) and Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China.
Sci China Life Sci. 2024 Nov;67(11):2411-2425. doi: 10.1007/s11427-024-2646-3. Epub 2024 Aug 21.
Switching from mitotic spermatogonia to meiotic spermatocytes is critical to producing haploid sperms during male germ cell differentiation. However, the underlying mechanisms of this switch remain largely unexplored. In Drosophila melanogaster, the gene RpL38 encodes the ribosomal protein L38, one component of the 60S subunit of ribosomes. We found that its depletion in spermatogonia severely diminished the production of mature sperms and thus led to the infertility of male flies. By examining the germ cell differentiation in testes, we found that RpL38-knockdown blocked the transition from spermatogonia to spermatocytes and accumulated spermatogonia in the testis. To understand the intrinsic reason for this blockage, we conducted proteomic analysis for these spermatogonia populations. Differing from the control spermatogonia, the accumulated spermatogonia in RpL38-knockdown testes already expressed many spermatocyte markers but lacked many meiosis-related proteins, suggesting that spermatogonia need to prepare some important proteins for meiosis to complete their switch into spermatocytes. Mechanistically, we found that the expression of bag of marbles (bam), a crucial determinant in the transition from spermatogonia to spermatocytes, was inhibited at both the mRNA and protein levels upon RpL38 depletion. We also confirmed that the bam loss phenocopied RpL38 RNAi in the testis phenotype and transcriptomic profiling. Strikingly, overexpressing bam was able to fully rescue the testis abnormality and infertility of RpL38-knockdown flies, indicating that bam is the key effector downstream of RpL38 to regulate spermatogonia differentiation. Overall, our data suggested that germ cells start to prepare meiosis-related proteins as early as the spermatogonial stage, and RpL38 in spermatogonia is required to regulate their transition toward spermatocytes in a bam-dependent manner, providing new knowledge for our understanding of the transition process from spermatogonia to spermatocytes in Drosophila spermatogenesis.
从有丝分裂精原细胞向减数分裂精母细胞的转变对于雄性生殖细胞分化过程中产生单倍体精子至关重要。然而，这种转变的潜在机制在很大程度上仍未被探索。在黑腹果蝇中，基因 RpL38 编码核糖体蛋白 L38，是核糖体 60S 亚基的一个组成部分。我们发现，在精原细胞中耗尽 RpL38 会严重减少成熟精子的产生，从而导致雄性果蝇不育。通过检查睾丸中的生殖细胞分化，我们发现 RpL38 敲低阻断了从精原细胞到精母细胞的转变，并在睾丸中积累了精原细胞。为了理解这种阻断的内在原因，我们对这些精原细胞群体进行了蛋白质组学分析。与对照精原细胞不同，RpL38 敲低睾丸中积累的精原细胞已经表达了许多精母细胞标记物，但缺乏许多减数分裂相关蛋白，这表明精原细胞需要为减数分裂准备一些重要的蛋白，以完成向精母细胞的转变。从机制上讲，我们发现 bag of marbles（bam）的表达，即从精原细胞向精母细胞转变的关键决定因素，在 RpL38 耗尽时，其 mRNA 和蛋白质水平都受到抑制。我们还证实，bam 的缺失表型与 RpL38 RNAi 在睾丸表型和转录组谱中的表型相似。引人注目的是，过表达 bam 能够完全挽救 RpL38 敲低果蝇的睾丸异常和不育，表明 bam 是 RpL38 调节精原细胞分化的关键下游效应物。总的来说，我们的数据表明，生殖细胞早在精原细胞阶段就开始准备减数分裂相关蛋白，而精原细胞中的 RpL38 以 bam 依赖的方式调节它们向精母细胞的转变，为我们理解果蝇生殖细胞从精原细胞到精母细胞的转变过程提供了新的知识。
