Differential expression of the nucleolar protein fibrillarin during mammalian spermatogenesis and its probable association with chromatoid body components.

Chromatoid body (CB) is a cytoplasmic structure of male germ cells that has been indicated as having a role in the RNA and protein storage for the final differentiation of spermatozoa. Recent studies have indicated that some of these macromolecular complex components have nucleolar origin. The aims of the present study were to monitor the expression of fibrillarin nucleolar protein in mammalian seminiferous tubules at different stages of the spermatogenic cycle; to check fibrillarin distribution during the CB assembly; and also its interaction with two well-known CB markers (MIWI and HSP70). Seminiferous tubules were isolated by transilluminating microscope from testis of adult mice. Fibrillarin expression and also co-localization between fibrillarin and MIWI/HSP70 were performed by Western blot (WB) and by immunofluorescence (IF), respectively. Total proteins from testis of adult mice were also used to perform co-immunoprecipitation (Co-IP) experiments. Our results demonstrated higher fibrillarin expression in seminiferous tubules in stages IV-VI, and a close localization of fibrillarin with MIWI (a protein that plays a role in RNA metabolism in the CB), as well as with HSP70 (a protein that plays a role in the proteasome folding in the CB). We also performed Co-IP between fibrillarin/MIWI and between fibrillarin/HSP70 in order to determine whether MIWI or HSP70 interacts with this nucleolar protein. We found MIWI in the Co-IP precipitate, but not HSP70. In conclusion, our results show that fibrillarin may participate in the physiological activities performed by the CB by interacting with CB components that play a role in RNA metabolism.