Multiple cell types in the oviduct express the prolactin receptor

Little is known about the physiological role of prolactin in the oviduct. Examining mRNA for all four isoforms of the prolactin receptor (PRLR) in mice by functional oviduct segment and stage of the estrous cycle, we found short form 3 (SF3) to be the most highly expressed, far exceeding the long form (LF) in highly ciliated areas such as the infundibulum, whereas in areas of low ciliation, the SF3 to LF ratio was ~1. SF2 expression was low throughout the oviduct, and SF1 was undetectable. Only in the infundibulum did PRLR ratios change with the estrous cycle. Immunofluorescent localization of SF3 and LF showed an epithelial (both mucosal and mesothelial) distribution aligned with the mRNA results. Despite the high SF3/LF ratio in densely ciliated regions, these regions responded to an acute elevation of prolactin (30 min, intraperitoneal), with LF-tyrosine phosphorylated STAT5 seen within cilia. Collectively, these results show ciliated cells are responsive to prolactin and suggest that prolactin regulates estrous cyclic changes in ciliated cell function in the infundibulum. Changes in gene expression in the infundibulum after prolonged prolactin treatment (7-day) showed prolactin-induced downregulation of genes necessary for cilium development/function, a result supporting localization of PRLRs on ciliated cells, and one further suggesting hyperprolactinemia would negatively impact ciliated cell function and therefore fertility. Flow cytometry, single-cell RNAseq, and analysis of LF-td-Tomato transgenic mice supported expression of PRLRs in at least a proportion of epithelial cells while also hinting at additional roles for prolactin in smooth muscle and other stromal cells.