Expression of genome defence protein members in proliferating and quiescent rat male germ cells and the Nuage dynamics

During epigenetic reprogramming germ cells activate alternative mechanisms to maintain the repression retrotransposons. This mechanism involves the recruitment of genome defence proteins such as MAEL, PIWIL4 and TDRD9, which associate with piRNAs and promote Line-1 silencing. MAEL, PIWIL4 and TDRD9 form the piP-bodies, which organization and dynamics vary according to the stage of germ cell epigenetic reprogramming. Although these data have been well documented in mice, it is not known how this mechanism operates in the rat. Thus, the aim of this study was to describe the distribution and interaction of MAEL, PIWIL4, TDRD9 and DAZL during rat germ cell development and check whether specific localization of these proteins is related to the distribution of Line-1 aggregates. Rat embryo gonads at 15 days post-conception (dpc), 16dpc and 19dpc were submitted to MAEL, PIWIL4, TDRD9 and DAZL immunolabelling. The gonads of 19dpc embryos were submitted to the double-labelling of MAEL/DAZL, TDRD9/MAEL and PIWIL4/MAEL. The 19dpc gonads were submitted to co-immunoprecipitation assays and fluorescent in situ hybridization for Line-1 detection. MAEL and TDRD9 showed very similar localization at all ages, whereas DAZL and PIWIL4 showed specific distribution, with PIWIL4 showing shuttling from the nucleus to the cytoplasm by the end epigenetic reprogramming. In quiescent 19dpc gonocytes all proteins colocalized in a nuage adjacent to the nucleus. DAZL interacts with PIWIL4 and MAEL, suggesting that DAZL acts with these proteins to repress Line-1. TDRD9, however, does not interact with DAZL or MAEL despite their colocalization. Line-1 aggregates were detected predominantly in the nuclear periphery, although did not show homogeneous distribution as observed for the nuage. In conclusion, the nuage in quiescent rat gonocytes show a very distinguished organization that might be related to the organization of Line-1 clusters and describe the association of DAZL with proteins responsible for Line-1 repression.