Complementary DNA cloning and expression of Pit-1/GHF-1 from the domestic turkey.

The transition from egg laying to incubation activity in birds is associated with a dramatic rise in serum prolactin levels. To further our understanding of the regulation of prolactin gene expression in birds, a cDNA clone encoding turkey Pit-1/GHF-1 was isolated. The turkey cDNA, designated tPit-1/GHF-1, was 1,123 nucleotides in length and encoded a protein of 327 amino acids, including a conserved 80-amino-acid POU-specific domain and a 60-amino-acid POU homeodomain. tPit-1/GHF-1 POU-specific domain and POU-homeodomain showed 94-95% amino acid identity with the corresponding rat Pit-1/GHF-1 domains. At its amino terminus, tPit-1/GHF-1 contained a 26-amino-acid insertion comparable to that found in the rat variant isoform, Pit-1 beta. Two other insertions of 38 and 7 amino acids were present and were not found in the mammalian protein. Levels of tPit-1/GHF-1 mRNA in pituitary tissue were examined at different phases of the turkey reproductive cycle by Northern blotting. tPit-1/GHF-1 mRNA was expressed as a 3.5-kb transcript, whose abundance remained relatively constant throughout the reproductive cycle. Thus, the dramatic rise in prolactin mRNA, observed during hyperprolactinemia in incubating turkey hens, was not associated with a concomitant increase in tPit-1/GHF-1 gene expression.