GSE121533
Ribosomal protein S5b is essential for oogenesis and is required to maintain mitochondrial integrity and function in Drosophila melanogaster
Increasing evidence indicates that ribosomes are heterogeneous and perhaps dynamic, in contrast to the classical view of them as constitutive machinery for protein synthesis [1-11]. In Drosophila melanogaster, nine ribosomal protein genes are each present in two paralogs, and in many of these cases one of the paralogs is primarily expressed in germline tissues [12-14]. Among these are two genes encoding ribosomal protein S5, called RpS5a and RpS5b. We demonstrate that RpS5b is specifically required for oogenesis. Females lacking RpS5b produce ovaries with polarity defects, fused egg chambers, and over-proliferation of posterior follicle cells.  Oogenesis ceases at stage 8-9, and widespread apoptosis follows.  Females lacking germline RpS5a are fully fertile, but germline expression of interfering RNA targeting RpS5a in an RpS5b mutant background worsens the RpS5b phenotype and causes complete germline lethality. A broad spectrum of mRNAs co-purified in immunoprecipitations with RpS5a, while RpS5b-associated mRNAs were specifically enriched for GO terms related to mitochondrial electron transport and cellular metabolic processes. Consistent with this, proteome comparison of wildtype and RpS5b ovaries revealed that RpS5b mitochondria were depleted for proteins linked to oxidative phosphorylation and mitochondrial respiration. As observed by immunohistochemical staining and transmission electron microscopy, RpS5b nurse cell mitochondria tended to form large clusters and had more heterogeneous morphology than those from controls. We also observed that RpS5b ovaries have elevated ROS, consistent with mitochondrial dysfunction. We conclude that RpS5b-containing ribosomes preferentially associate with mRNAs encoding mitochondrial components and serve an essential function in oogenesis. Overall design: The mRNAs associated to either RpS5b and RpS5a were identified by co-IP followed by deep sequencing. The mRNAs enriched to either of the two parologs of RpS5, when applicable, were analyzed in three genetic backgrounds, wildtype, RpS5b-null and the ovary with germline RpS5a knocked down by RNAi.