Long poly(A) tails of neuropeptide mRNAs originate in the cytoplasm of neurosecretory cells

Specialized secretory neurons in the hypothalamus and the Edinger-Westphal nucleus secrete severalneurohormones. Very little is known about the regulation of their expression at the post-transcriptionallevel. Here we discovered that a non-canonical cytoplasmic poly(A) polymerase Tent5a is a globalpositive regulator of neurohormone expression. We detect Tent5a in Edinger-Westphal, paraventricularand supraoptic nuclei, as well as the lateral hypothalamic area. Importantly, RNA sequencing of theseregions’ biopsies, as well as northern analysis of the whole hypothalami, revealed decreased expressionof several neuropeptides mRNA in tent5a knockout mice, like vasopressin, oxytocin, urocortin, and CARTpeptide. In contrast, corticotropin-releasing factor expression, for instance, remained unchanged bothon mRNA and protein levels, indicating selectivity of Tent5a targets. To check if Tent5a directlypolyadenylates downregulated mRNAs, we performed genome-wide poly(A) tail length profiling of RNAfrom the hypothalamus on the Oxford Nanopore platform. Such analysis revealed that mRNAs encodingvasopressin and oxytocin have greatly reduced poly(A) tail length (from ~200 to ~100bp), which is notrestored to the physiological levels upon dehydration.Our results indicate a novel mechanism of ensuring efficient baseline neuropeptide secretion bystabilizing their mRNAs with Tent5a-mediated polyadenylation in the cytoplasm.