The transient Spt4-Spt5 complex as an upstream regulator of non-coding RNAs during development

ABSTRACT: 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 (micronucleus - MIC) and somatic nuclei (macronucleus - MAC), 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. As we were mostly interested in transcription of the germline genome in the MIC during meiosis, we decided to probe the composition of the Spt5-Spt4 complex characteristic to this nucleus. Experiments in which Spt4mB-3xFLAG was used as bait demonstrated its interaction with either Spt5m or Spt5v, which is consistent with the Spt4mB-GFP localization pattern. Interestingly, mass spectrometry revealed that Spt5m-3xFLAG (which is present only in the MIC at the analyzed stage) interacts either with the meiotic Spt4mB or with Spt4vA. 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.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Paramecium Tetraurelia

SUBMITTER: Agata Malinowska  

LAB HEAD: Jacek K. Nowak

PROVIDER: PXD027748 | Pride | 2022-04-27

REPOSITORIES: Pride