Decifring the role of transient proteins in the chromatoid bodies molecular composition: Fibrillarin (nucleolar component) and CLOCK/BMAL1 (circadian proteins).

Abstract

The chromatoid body (CB) is a cytoplasmic structure of male germ cells that has a role in the regulation of mRNA transcription during spermatogenesis, and participates in the control of gene expression through the action of small non-coding RNAs (pi and miRNAs). Recent studies have demonstrated that this entire small mRNA metabolism mediated by non-coding RNAs executed by the CB is crucial for the spermatogenesis process and it ensures the formation of the mature male reproductive cell. The complete proteome analysis of CB molecular structure identified abundant presence of their classical molecular markers (MVH, Miwi, DDX25, TDRD6 and TDRD7), but also identified a large number of transient proteins, or proteins having temporarily nuclear function / localization before being found in the CB. Transient protein that has drawn the attention of our group are: nucleolar protein fibrillarin (rRNA 2'-O-methyltransferase) and the protein CLOCK (circadian locomoter output cycles kaput protein) and BMAL1 (brain and muscle ARNT-Like 1), which are molecular components of the circadian control. The nucleolus is a sub-compartment of the nucleus, which has the primary function in the biogenesis of ribosomes and studies have shown that the nucleolar cycle during gametogenesis contributes to the reestablishment of nucleolar morphology during gametogenesis, being an important factor for removal of induced cell damage by aging. Thus, the CB could be participating in this cycle harboring some nucleolar proteins that were being reorganized in this cycle. Furthermore, the identification of BMAL1 and CLOCK proteins in the molecular composition of CBs plus the fact that BMAL1 mice present sterility and morphological changes in the CB of post-meiotic cells are evidence that lead us to try to correlate the role of these two proteins in the CBs physiology. Therefore, the aim of this study is to test two initial hypothesis by conducting experiments that allow us to highlight the nucleolar activity influence on post-meiotic CBs organization; to verify that the morphological changes observed in CBs of post-meiotic cells in BMAL1 knockout mice are actually produced by ablation of BMAL1 or whether they were related to the accelerated aging process that this ablation promotes on these biological models. (AU)