A study of the expression of germline-specific paralogs of the ubiquitously expressed NAC complex revealed their association with centrosomes

Abstract

Protein homeostasis involves the ubiquitously expressed heterodimeric protein NAC (ribosome associated nascent polypeptide complex), consisting of - and {beta}-subunits. We previously found in Drosophila melanogaster the presence of germline-specific paralogous genes for NAC subunits (gNACs): unique for the -subunit and several highly homologous amplified genes for the {beta}-subunit, indistinguishable by the antibodies used, while they were detected as different phosphorylated isoforms in 2D electrophoresis with immunostaining. The distinct increase in gNAC expression in growing spermatocytes compared with their predecessors, gonioblasts, is accompanied by a clear presence of gNAC in the cytoplasm of dividing meiotic cells and spermatids. In oogenesis, gNAC expression is significantly lower than in the testis, but gNAC accumulation is found at the posterior pole of the mature oocyte, known as the germplasm region responsible for the germ cell formation in the offspring. gNAC-associated ribosomes from mature oocytes are enriched in mRNA sets encoding known germplasm and centrosome proteins. gNAC is also detected in a pericentriolar component of centrosomes: in syncytial dividing nuclei in the early embryos, in primordial germ cells and spermatocytes, including meiotic divisions stage. CRISPR/Cas9-mediated deficiency of the gNAC-alpha subunit causes female infertility. We propose the role of the gNAC phosphoregulatory paralog system as a component of the germline proteostasis network, coordinated with the centrosome functions. Here, we also extended our results by identifying cross-links between ubiquitous and germline-specific NAC-{beta} paralogs, finding an additional case of functional cross-talk between heterodimeric ubNAC and gNAC -subunit paralogs, which may maintain the robustness of proteostasis and fly fecundity.