Linker histones H1 are essential chromatin components that exist as multiple developmentally regulated variants. In metazoans, specific H1s are expressed during germline development in a tightly regulated manner. However, the mechanisms governing their stage-dependent expression are poorly understood. Here, we address this question in Drosophila, which encodes for a single germline-specific dBigH1 linker histone. We show that during female germline lineage differentiation, dBigH1 is expressed in germ stem cells and cystoblasts, becomes silenced during transit-amplifying (TA) cystocytes divisions to resume expression after proliferation stops and differentiation starts, when it progressively accumulates in the oocyte. We find that dBigH1 silencing during TA divisions is post-transcriptional and depends on the tumour suppressor Brain tumour (Brat), an essential RNA-binding protein that regulates mRNA translation and stability. Like other oocyte-specific variants, dBigH1 is maternally expressed during early embryogenesis until it is replaced by somatic dH1 at the maternal-to-zygotic transition (MZT). Brat also mediates dBigH1 silencing at MZT. Finally, we discuss the situation in testes, where Brat is not expressed, but dBigH1 is translationally silenced too.

接头组蛋白 H1 是重要的染色质成分，以多种发育调控的变体形式存在。在后生动物中，特定的 H1s 在种系发育过程中以一种严格调控的方式表达。然而，人们对控制其阶段依赖性表达的机制知之甚少。在这里，我们在果蝇中解决这个问题，它编码单个种系特异性 dBigH1 接头组蛋白。我们表明，在雌性生殖系谱系分化过程中，dBigH1 在生殖干细胞和成囊细胞中表达，在转运扩增 (TA) 囊细胞分裂过程中变得沉默，以在增殖停止和分化开始后恢复表达，此时它逐渐在卵母细胞中积累。我们发现 TA 分裂期间的 dBigH1 沉默是转录后的，并且取决于肿瘤抑制因子脑肿瘤 (Brat)，这是一种调节 mRNA 翻译和稳定性的必需 RNA 结合蛋白。与其他卵母细胞特异性变体一样，dBigH1 在早期胚胎发生期间母体表达，直到在母体-合子转换 (MZT) 时被体细胞 dH1 取代。Brat 还介导 MZT 的 dBigH1 沉默。最后，我们讨论睾丸的情况，