Regulation of pigeon crop gene expression by prolactin.

The pigeon crop has long been known as a target tissue for PRL action. This study investigates the molecular events associated with PRL stimulation of the pigeon crop sac. Several experiments were performed comparing isolates from PRL-injected pigeons (200 micrograms/day, im, for 3 days) to saline-treated pigeons. Electrophoretic analysis of crop protein revealed a general pattern of similarity between PRL-stimulated and control isolates, but four major polypeptides were distinctly dissimilar. Two crop peptides (CP) migrating at molecular weight 16,400 and 29,900 (CP16, CP30) were selectively repressed by PRL treatment. In contrast, two products, CP25 and CP154, were dramatically induced in PRL-stimulated crops. Short (4-h) in vivo labeling using tritiated amino acids revealed that polypeptides comigrating with CP16 and CP30 were synthesized only in control crops. A product migrating with CP25 was selectively labeled in PRL-induced crop tissue. To investigate PRL's effect on mRNA populations, polyadenylated RNA was isolated from control or PRL-stimulated crops and translated in a reticulocyte lysate translation system. Gel electrophoresis and fluorography revealed PRL treatment to cause two major differences in the mRNA fractions: repression of a translatable mRNA coding for a product comigrating with CP16 and a large increase in presumptive CP25 mRNA (to 14% of the translatable message). Translation product profiles of mRNA isolated from crops treated locally revealed a dependence of CP25 mRNA induction on the dose of PRL (16-25 micrograms/day). These results show that PRL acts in a direct manner on the crop to regulate specific gene products. Control of two products results from alteration of mRNA levels.