The role of the pAbp gene encoding the cytoplasmic poly(A)-binding protein in spermatogenesis of Drosophila melanogaster
The Drosophila melanogaster pAbp gene encodes the cytoplasmic poly(A)-binding protein (PABP). Cytoplasmic PABPs participate in the metabolic pathways of the mRNA: translation initiation and termination, cytoplasmic polyadenylation/deadenylation, mRNA stability, mRNA degradation. Despite the extensive biochemical and structural characterization, relatively little is known about the biological roles of PABPs in the processes of cellular development and differentiation. In Drosophila spermatogenesis, posttranscriptional mechanisms of gene regulation play an important role, so cytoplasmic PABP can have significant function in this process. Deletion of PABP leads to embryonic lethality. However, some flies carrying combinations of mutant pAbp alleles survive but display male sterility and show defects in spermatogenesis. It has previously been shown that hypomorphic pAbp mutations cause a number of meiotic defects, abnormalities of Nebenkern formation. These data provide an insight into the effect of pAbp mutation on the individual events of spermatogenesis, but they do not cover the entire process. We studied spermatogenesis in pAbp allele heterozygotes by transmission electron and fluorescent light microscopy. We showed that cellular mitochondria were the primary structural target of the mutation. Abnormal mitochondria were less structured, swollen, had transparent matrix and depleted cristae. Further mutation had a polymorphous effect and induced anomalies in the ultrastructure of mature spermatocytes, defects in Nebenkern formation and division, axial complex formation, shutdown of spermatogenesis during spermatid elongation. Thus our data show a significant role of PABP in structural transformations of male germ cells during entire spermatogenesis.