Prolactin receptor gene expression in the brain and peripheral tissues in broody and nonbroody breeds of domestic hen.

The objective of this study was to establish whether the gene encoding prolactin receptor (PRLR) is expressed in the hypothalamus and peripheral tissues of the domestic chicken and, if so, to determine whether there are breed differences in the structure or expression of the gene which might account for the observation that broodiness does not occur in the White Leghorn hen but does occur in other breeds of domestic hens, including the bantam. A preliminary experiment demonstrated that the absence of broodiness in White Leghorns is not due to a lack of a prolactin response to the avian prolactin-releasing hormone vasoactive intestinal polypeptide. The largest amounts of PRLR mRNA in the brain, which did not differ significantly between laying White Leghorns and bantams, were found in the pituitary gland and basal and preoptic hypothalamus. Small or nondetectable amounts were found in both breeds in the forebrain, cerebellum, and optic lobes. Prolactin receptor mRNA was widely distributed in peripheral tissues in both breeds, in the following descending order of abundance: kidney, leg skin, brood patch, duodenum, intestine > thyroid gland > adrenal gland, liver, ovary >> adipose tissue > thymus, spleen > muscle > blood. Southern blotting analysis using four restriction enzymes and a chicken PRLR cDNA probe demonstrated identical digestion patterns for White Leghorn and bantam genomic DNA. Northern blotting analysis identified two sizes of chicken PRLR mRNA transcripts (7.5 and 3.3 kb) in hypothalami from laying White Leghorn and bantam hens. It is concluded that differences in the expression of broodiness in White Leghorn and bantam hens cannot be explained by differences in the amounts of PRLR mRNA in the hypothalamus or in the transcription or gross structure of the PRLR gene.