| Summary: | Immunohistochemical studies localised PRL expression to the stromal compartment of the marmoset endometrium. Expression was minimal during the proliferative phase and was up-regulated during the mid-late secretory phase of the ovulatory cycle. Similarly to PRL, PRL-R expression was minimal during the proliferative phase and was dramatically up-regulated during the mid-late secretory phase. However, expression of the PRL-r was localised to the glandular epithelium of the endometrium. The temporal pattern of PRL-R gene expression in the marmoset uterus across the ovulatory cycle was further confirmed by ribonuclease protection assay. The role of Jak2, Stat1 and Stat5 in the intracellular signalling pathway of PRL were also assessed in the mid-late secretory phase. Jak2/Stat1/Stat5 proteins were co-localised with the PRL-R to the glandular epithelial compartment. Moreover within the marmoset uterus, Jak2, Stat1 and Stat5 were temporarily phosphorylated in response to PRL. The pattern of expression of the IRF-1 gene, a PRL target gene, and the effect of PRL on transcription of IRF-1 were also investigated. IRF-1 expression in the marmoset uterus was encoded by a protein of 48 kDa and was localised to the glandular epithelial compartment, as was observed for the PRL-R and Jak2/Stat1/Stat5 proteins. Incubation of mid-late secretory uterine tissue with PRL for 3 hours resulted in 2.4 ± 0.5 (P<0.05) fold induction of IRF-1 gene expression. These studies confirm (a) high sequence and functional similarity between the marmoset and human PRL-R and (b) the expression of both PRL and its receptor in the uterus of the marmoset monkey. Expression of both genes is up-regulated during the mid-late secretory phase of the ovulatory cycle. PRL function in the marmoset uterus is linked to the Jak/Stat signalling pathway leading to the regulation of expression of PRL-responsive genes such as IRF-1. The site of expression of PRL, PRL-R and IRF-1 in the marmoset uterus suggest that PRL may influence glandular epithelial function and direct gene transcription in these cells in a paracrine fashion. In conclusion, the data strongly suggest that the marmoset monkey may provide a useful tool to investigate the role of PRL in human reproduction.
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