The turkey transcription factor Pit-1/GHF-1 can activate the turkey prolactin and growth hormone gene promoters in vitro but is not detectable in lactotrophs in vivo

The transcription factor Pit-1/GHF-1 plays an important role in regulating the prolactin (Prl) and growth hormone (GH) genes in mammals. In this study , the role that Pit-1 plays in regulating the prolactin and growth hormone genes in avian species was examined by cotransfection assays and immunofluo rescence staining of pituitary sections. In cotransfection assays, turkey P it-1 activated the turkey Prl, turkey GH, and rat Prl promoters 3.8-, 3.7-, and 12.5-fold, respectively. This activation was comparable to rat Pit-1 a ctivation of these same promoters. A point mutation in the turkey Pit-1 cDN A, which changed leu-219 to ser-219, resulted in a 2-, 2-, and 10-fold redu ction in the activation of the turkey Prl, turkey GH, and rat Prl promoters , respectively. Unexpectedly, coexpression of tPit-1 (leu-219) and tPit-1(s er-219) activated turkey Prl and rat Prl promoters 9.4- and 35.9-fold, resp ectively, but had no effect on the turkey GH promoter. Dual-label immunoflu orescence analysis of turkey pituitary sections revealed that Pit-1 was not detectable in prolactin-staining cells but was detectable in GH-staining c ells. Taken together, these data indicate that in the domestic turkey, Pit- 1 can activate the turkey Prl promoter in vitro, but does not appear to pla y a role in regulating Prl gene expression in vivo. Pit-1, however, still l ikely plays a role in regulating GH gene expression. (C) 2001 Academic Pres s.