Changes in prolactin receptor expression during pregnancy in the mouse ovary.

We have isolated the cDNA encoding the cytoplasmic domain of a long form of the mouse PRL receptor (PRL-R). The mRNA for this long form PRL-R and the three mRNAs encoding short mouse PRL-R that have been previously characterized are all expressed in both the liver and ovary. The relative amounts of these receptor forms differ between tissues, however. In addition, the structure of one of the short receptor forms may not be identical in the liver and ovary. Within the ovary, the abundance and sites of synthesis of the four PRL-R mRNAs vary during pregnancy. Expression of the two most abundant PRL-R mRNAs increases significantly at midgestation. Expression of PRL-R mRNA is detected in the corpus luteum throughout pregnancy, while increased receptor mRNA levels are evident in the granulosa cells of a subset of Graafian follicles toward the end of pregnancy and during lactation. Some differences are also observed in the expression patterns of the individual receptor forms. Most notably, one of the short form PRL-R mRNAs is uniquely detected in atretic follicles in early to midgestation.