Rodents possess an expanded prolactin (PRL) family of genes. These genes encode for a family of structurally related hormones/cytokines that are expressed most prominently in the anterior pituitary, uterus and placenta. In this study, we have identified a new member of the rat PRL family through a search of the National Center for Biotechnology Information expressed sequence database. The cDNA was sequenced and its corresponding mRNA characterized. On the basis of existing nomenclature, the rat cDNA was termed PRL-like protein-N (PLP-N). PLP-N has structural features indicative of its inclusion in the PRL family and is most closely related to PRL-like protein-F (PLP-F) and proliferin related protein (PLF-RP). A survey of PLP-N mRNA expression by Northern analysis indicated that PLP-N showed extensive expression in the metrial gland and minimal expression in the chorioallantoic placenta or other tIssues. Expression of PLP-N mRNA was restricted to migratory trophoblast cells. Junctional zone trophoblast cells isolated from day 13 of gestation placenta differentiated in vitro and exhibited a capacity for PLP-N expression. In summary, we have discovered a new member of the PRL family that is prominently expressed in migratory trophoblast cells residing in the metrial gland.

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