Expression of the prolactin receptor gene during the breeding and non-breeding seasons in red deer (Cervus elaphus): evidence for the expression of two forms in the testis.

The red deer is a seasonally breeding mammal with a circannual cycle of prolactin secretion which reaches its peak during the non-breeding season. This study investigated expression of the prolactin receptor gene in red deer tissues collected in the breeding and non-breeding seasons. A 562 bp fragment of the extracellular domain of the red deer prolactin receptor cDNA was amplified from red deer liver poly(A)+ RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) using primers designed from the human sequence. Northern blots were prepared using 10-20 micrograms poly(A)+ RNA. The blots were hybridized to the 562 bp cDNA labelled by random priming with alpha 32P-dCTP. A main transcript of 3.5 kb was expressed in liver, heart, kidney and testis throughout the year and in epididymis during the breeding season only. In the testis an additional major transcript of 1.7 kb was present during the breeding and non-breeding seasons. Competitive binding assays using 125I-ovine prolactin (125I-oPRL) were performed on microsomal membrane fractions prepared from liver. Scatchard analyses confirmed the presence of a single class of lactogen-binding receptor with a mean Ka of 0.87 +/- 0.12 x 10(9) M-1 and a Bmax of 73.6 +/- 9.8 fmol/mg protein (n = 5). Cross-linking of 125I-oPRL to liver microsomes with 0.5 mM disuccinimidyl suberate followed by SDS-PAGE revealed a major band of molecular mass 56 kDa which was displaced by ovine prolactin, suggesting a specific lactogen-binding entity of 33 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)