PMON29 A Comparative Analysis of Musashi-Dependent Control of Mouse and Human Pituitary mRNA Translation

Specialized cell lineages within the anterior pituitary produce specific hormones which, in turn, regulate diverse biological processes ranging from growth, metabolism, and reproduction to stress. Interestingly, these specialized cell lineages exhibit a high degree of cellular plasticity, readily altering their differentiation state to produce different hormones in response to organismal demand. Underlying molecular mechanisms controlling cellular plasticity in the pituitary are not fully defined but appear to involve post-transcriptional regulation exerted by the Musashi family of sequence-specific RNA binding proteins. Musashi is a bifunctional regulator of target mRNAs and can exert either repression or activation of translation in a context-dependent manner. Our recent work has implicated a role for Musashi-dependent repression of key pituitary mRNAs in the mouse, including a lineage-specific transcription factor (Pou1f1), the gonadotropin releasing hormone receptor (Gnrhr), and two anterior pituitary hormones (Prl and Tshb). In this study, we look to determine the potential relevance of Musashi-dependent mRNA translational control to the human pituitary. Reflecting our findings in the adult mouse, a re-analysis of published human fetal pituitary single cell RNA sequencing data revealed Musashi1 (MSI1) and Musashi2 (MSI2) expression in both stem/progenitor cell populations as well as in all hormone-producing cell lineages of the anterior pituitary. We further report that the human homologs of identified Musashi-target mRNAs in the mouse pituitary also possess Musashi binding elements (MBEs) in their 3' untranslated regions (UTRs). In the case of the human Pou1f1 3' UTR, we were able to verify Musashi-dependent mRNA translational repression in reporter assays as seen with the murine Pou1f1 3' UTR. Interestingly, a germline Pou1f1 mutation identified in human patients, disrupts a consensus MBE in the human Pou1f1 3' UTR and abolishes Musashi-dependent repression. We developed a bioinformatic pipeline to characterize pathogenic human mutations catalogued in the Geno2MP database for disruption or creation of consensus MBEs in pituitary-specific mRNA 3' UTRs. Our findings suggest an evolutionarily conserved role for Musashi in the post-transcriptional regulation of pituitary mRNAs in both mice and humans and identify several human mutations which may perturb Musashi regulation of human pituitary function. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.