Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland.
Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France.
Nucleic Acids Res. 2022 Mar 21;50(5):2603-2620. doi: 10.1093/nar/gkac106.
The Spt4-Spt5 complex is conserved and essential RNA polymerase elongation factor. To investigate the role of the Spt4-Spt5 complex in non-coding transcription during development, we used the unicellular model Paramecium tetraurelia. In this organism harboring both germline and somatic nuclei, massive transcription of the entire germline genome takes place during meiosis. This phenomenon starts a series of events mediated by different classes of non-coding RNAs that control developmentally programmed DNA elimination. We focused our study on Spt4, a small zinc-finger protein encoded in P. tetraurelia by two genes expressed constitutively and two genes expressed during meiosis. SPT4 genes are not essential in vegetative growth, but they are indispensable for sexual reproduction, even though genes from both expression families show functional redundancy. Silencing of the SPT4 genes resulted in the absence of double-stranded ncRNAs and reduced levels of scnRNAs - 25 nt-long sRNAs produced from these double-stranded precursors in the germline nucleus. Moreover, we observed that the presence of a germline-specific Spt4-Spt5m complex is necessary for transfer of the scnRNA-binding PIWI protein between the germline and somatic nucleus. Our study establishes that Spt4, together with Spt5m, is essential for expression of the germline genome and necessary for developmental genome rearrangements.
Spt4-Spt5 复合物是保守且必不可少的 RNA 聚合酶延伸因子。为了研究 Spt4-Spt5 复合物在发育过程中非编码转录中的作用，我们使用单细胞模式生物四膜虫。在这个具有生殖核和体细胞核的生物体内，整个生殖系基因组在减数分裂期间发生大量转录。这种现象引发了一系列由不同种类的非编码 RNA 介导的事件，这些 RNA 控制着发育编程的 DNA 消除。我们的研究集中在 Spt4 上，它是四膜虫中由两个基因编码的一种小锌指蛋白，这两个基因在有丝分裂期间持续表达，两个基因在减数分裂期间表达。SPT4 基因在营养生长中不是必需的，但在有性生殖中是必不可少的，尽管来自这两个表达家族的基因具有功能冗余性。沉默 SPT4 基因导致双链 ncRNA 缺失，并且从这些双链前体在生殖细胞核中产生的 25nt 长的 scnRNA 水平降低。此外，我们观察到，生殖系特异性 Spt4-Spt5m 复合物的存在对于 scnRNA 结合的 PIWI 蛋白在生殖系和体细胞核之间的转移是必需的。我们的研究确立了 Spt4 与 Spt5m 一起对于生殖系基因组的表达是必不可少的，并且对于发育过程中的基因组重排也是必需的。
