The Drosophila ribosome protein S5 paralog RpS5b promotes germ cell and follicle cell differentiation during oogenesis

Abstract

Emerging evidence suggests that ribosome heterogeneity may have important functional consequences in the translation of specific mRNAs within different cell types and under various conditions. Ribosome heterogeneity comes in many forms including post-translational modification of ribosome proteins (RPs), absence of specific RPs, and inclusion of different RP paralogs. The Drosophila genome encodes two RpS5 paralogs, RpS5a and RpS5b. While RpS5a is ubiquitously expressed, RpS5b exhibits enriched expression in the reproductive system. Deletion of RpS5b results in female sterility marked by developmental arrest of egg chambers at stages 7-8, disruption of vitellogenesis, and posterior follicle cell (PFC) hyperplasia. While transgenic rescue experiments suggest functional redundancy between RpS5a and RpS5b, molecular, biochemical, and ribo-seq experiments indicate that RpS5b mutants display increased rRNA transcription and RP production, accompanied by increased protein synthesis. Loss of RpS5b results in microtubule-based defects and mislocalization of Delta and Mindbomb1, leading to failure of Notch pathway activation in PFCs. Together, our results indicate that germ cell specific expression of RpS5b promotes proper egg chamber development by ensuring the homeostasis of functional ribosomes.

mRNA Translation Is Dynamically Regulated to Instruct Stem Cell Fate

“…Intriguingly, mESCs display different ribosome subunit stoichiometries in monosomes and polysomes, and these associate with different mRNAs ( Shi et al, 2017 ). Recent work in the Drosophila germline has shown that a paralogue of RpS5 is required for normal progression of differentiation and preferentially promotes translation of a subset of transcripts ( Kong et al, 2019 ; Jang et al, 2021 ). These tantalizing observations raise the possibility that different incorporation of ribosomal subunits into ribosomes may regulate stem cell behavior; however, this has not yet been demonstrated.…”

Pseudouridine-dependent ribosome biogenesis regulates translation of polyglutamine proteins during Drosophila oogenesis

“…In addition, loss of Nop10 and Nop60B resulted in cysts with hypertrophic nucleoli compared to wild-type cysts, suggesting a ribosome biogenesis defect ( Figure S5C-S5F ) (Neumüller et al, 2008; Sanchez et al, 2016). To verify that the H/ACA box deposits pseudouridine on rRNA during oogenesis, we co-immunopurified the 40S and 60S ribosomal subunits from the germline, utilizing a germline-enriched HA-tagged ribosomal protein RpS5b ( Figure S5G-S5I ) (Jang et al, 2021) (Chen and Dickman, 2017). Mass spectrometry analysis showed that loss of the H/ACA box member Nop10 led to a significant decrease of pseudouridine on rRNA relative to controls ( Figure 3A, Supplemental Table 3 ).…”

“…This hypothesis predicts that compromised ribosome biogenesis will phenocopy loss of H/ACA box components. We impaired ribosome biogenesis by depleting ribosomal protein paralogs RpS10b and RpS19b in the germline, as the depletion of other ribosomal proteins that do not have paralogs results in GSC differentiation defects or loss of cyst stages that would mask the cyst differentiation block (Jang et al, 2021; Martin et al, 2021; McCarthy et al, 2022; Sanchez et al, 2016). Depletion of RpS10b and RpS19b phenocopied loss of H/ACA box components, leading to a block in cyst differentiation and decreased levels of Rbfox1 and Bru1 proteins without a concomitant loss of their mRNAs ( Figure S7A-S7K, S8A-S8H ).…”

IQCN disruption causes fertilization failure and male infertility due to manchette assembly defect

“…Above, we speculated that variants in IQCN may disturb the function of IFT‐related proteins via calmodulin regulation, and found that ribosomal protein family members are downregulated under IQCN knockout. A previous study suggested that ribosomal protein loss is associated with microtubule‐based defects (Jang et al , 2021 ); however, the exact regulatory mechanism and the role in spermiogenesis require further investigation.…”