Differentiation of syncytialized trophoblasts elicits widespread 3’UTR shortening that accompanies increased cellular function in protein secretion

Most eukaryotic genes express alternative polyadenylation (APA) isoforms with different 3’UTR sizes. The APA profile varies across tissue types and under different growth and differentiation conditions. Here we report that, unlike many other cell differentiation lineages, differentiation of syncytiotrophoblasts (SCTs) elicits widespread 3’UTR shortening, as shown in multiple in vitro trophoblast differentiation models as well as in single placental cells at different stages of pregnancy. We show that the 3’UTR shortening is unrelated to cell proliferation, a feature previously associated with 3’UTR size control, but rather accompanies increased cell function in protein secretion. In addition, 3’UTR shortening correlates with increased transcript abundance and is coupled with enhanced intronic APA site usage, suggesting activation of 3’ end processing in SCT differentiation. Together, our data indicate that SCTs utilize APA to express transcripts with short 3’UTRs, which may enhance hormone production and secretion, contributing to their functions in pregnancy.