EXPRESSION OF THE PROLACTIN RECEPTOR GENE DURING THE BREEDING AND NON-BREEDING SEASONS IN RED DEER (CERVUS-ELAPHUS) - EVIDENCE FOR THE EXPRESSION OF 2 FORMS IN THE TESTIS

The red deer is a seasonally breeding mammal with a circannual cycle o f prolactin secretion which reaches its peak during the non-breeding s eason. This study investigated expression of the prolactin receptor ge ne in red deer tissues collected in the breeding and non-breeding seas ons. A 562 bp fragment of the extracellular domain of the red deer pro lactin receptor cDNA was amplified from red deer liver poly(A)(+) RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) using prim ers designed from the human sequence. Northern blots were prepared usi ng 10-20 mu g poly(A)(+) RNA. The blots were hybridized to the 562 bp cDNA labelled by random priming with alpha(32)P-dCTP. A main transcrip t of 3.5 kb was expressed in liver, heart, kidney and testis throughou t the year and in epididymis during the breeding season only. In the t estis an additional major transcript of 1.7 kb was present during the breeding and non-breeding seasons. Competitive binding assays using I- 125-ovine prolactin (I-125-opRL) were performed on microsomal membrane fractions prepared from Liver. Scatchard analyses confirmed the prese nce of a single class of lactogen-binding receptor with a mean K-a of 0.87 +/- 0.12 x 10(9) M(-1) and a B-max of 73.6 +/- 9.8 fmol/mg protei n (n=5). Cross-linking of I-125-opRL to liver microsomes with 0.5 mM d isuccinimidyl suberate followed by SDS-PAGE revealed a major band of m olecular mass 56 kDa which was displaced by ovine prolactin, suggestin g a specific lactogen-binding entity of 33 kDa. This study confirms th e expression of the red deer prolactin receptor gene throughout the ye ar, characterizes the prevalent form of receptor in the liver and demo nstrates the expression of a separate, short form in the testis.