TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION OF PROLACTIN DURING THE TURKEY REPRODUCTIVE-CYCLE

The present study examined turkey prolactin (PRL) transcription and PR L mRNA stability during different reproductive stages. Nuclear run-on transcription assays were performed using isolated nuclei from pituita ries of turkeys at different reproductive stages. Meanwhile, cytoplasm ic PRL mRNA and plasma PRL were measured by slot blot and RIA respecti vely. The PRL transcription, pituitary cytoplasmic PRL mRNA abundance and plasma PRL levels increased after photostimulation and peaked at t he incubating stage (P < 0.05). A decrease in PRL transcription, pitui tary cytoplasmic PRL mRNA and plasma PRL (P < 0.05) was observed durin g the transition from incubation to photorefractoriness. Nest-deprivat ion reduced circulating PRL (P < 0.05), whereas pituitary cytoplasmic PRL mRNA and PRL transcription were not significantly altered from tho se in incubating birds (P > 0.05). The half-life of PRL mRNA was deter mined in pituitaries of non-photostimulated, laying, incubating and ph otorefractory hens. Primary pituitary cell cultures were treated with the transcription inhibitor actinomycin-D and the decay of the pre-exi sting PRL mRNA was quantified using Northern blot analysis. The PRL mR NA half-life was 1.5- and 1.4-fold greater in incubating and laying bi rds respectively than in non-photostimulated turkeys (P < 0.05). The h alf-life of PRL mRNA in photorefractory and incubating hens was simila r in spite of great differences in pituitary PRL mRNA steady-state lev els and PRL transcription. Our data suggest that photoinduced changes in pituitary PRL mRNA and plasma PRL are due to changes in both PRL tr anscription and PRL mRNA stability. Nest-deprivation inhibits the PRL releasing mechanism(s) independently of PRL transcription in turkeys.