Post-transcriptional regulation of stem and progenitor cell function

ABSTRACT The genome is transmitted from one generation to the next by two highly specialized cell types, sperm and egg. In the adult testis, spermatogonial stem cells continuously produce progenitors that rapidly expand their population (transit-amplify) before undergoing terminal differentiation into sperm. Across tissues, cell state transitions from stem cell to progenitor to differentiated cell require regulated gene expression programs. Post- transcriptional mechanisms that regulate RNA, from splicing through translation, play a major role in shaping these gene expression programs. My research program seeks to define how post-transcriptional regulation shapes gene expression programs to support the function of spermatogonial stem and progenitor cells, using mouse as our model. We leverage single cell methods as well as approaches unique to spermatogenesis to provide enhanced stage-specific insights into progenitor function. We will focus on two Areas: Area 1: During spermatogenesis, retinoic acid (RA) signaling induces early progenitors to form committed progenitors via canonical regulation of transcription and noncanonical regulation of translation. We have demonstrated that RNA-binding protein and translational regulator DAZL supports the formation of committed progenitors, but whether DAZL’s activity affects RA-induced molecular changes remains unclear. Here, we will test the hypothesis that DAZL enhances RA-mediated changes in transcription and translation to induce formation of committed progenitors. Area 2: Committed spermatogonial progenitors enter terminal differentiation when they initiate meiosis in response to RA signaling. RA activates gene expression of Stra8 and Meiosin, which encode a heterodimeric transcription factor that drives the initiation of meiosis. We recently discovered that the RA-dependent upregulation of Meiosin gene expression requires the RNA-binding complex MEIOC-YTHDC2-RBM46, which mediates mRNA degradation of transcriptional repressors of Meiosin. Based on these data, we proposed the conceptually novel model that committed progenitors must acquire the molecular competence to initiate meiosis in response to RA. Furthermore, this competence is regulated by MEIOC-YTHDC2-RBM46 destabilizing mRNA. Here, we propose to expand on this model. We will define the mechanism by which MEIOC-YTHDC2-RBM46-bound mRNAs are degraded, identify MEIOC’s molecular function within the complex, and determine whether genetic ablation of transcriptional repressors targeted by MEIOC-YTHDC2- RBM46 is sufficient to rescue the competence of Meioc knockout committed progenitors. Our proposed research directions will define how post-transcriptional regulation interacts with transcriptional networks to support spermatogonial stem and progenitor cell function, with implications for human reproductive health. More broadly, our studies will inform how post-transcriptional mechanisms may be implemented in other contexts of normal cellular differentiation and co-opted in cancer.