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ABSTRACT

cDNAs encoding the precursor molecule of the turkey LH β subunit (tLHβ) were cloned from a turkey pituitary cDNA library. The nucleotide sequence of the longest of two different tLHβ cDNA clones contained 592 bp, and included 23 bp of the 5′ untranslated region (UTR) and 92 bp of the 3′ UTR in addition to a 477 bp open reading frame that encoded a 39 amino acid leader polypeptide and a 120 amino acid mature apoprotein. Turkey and chicken LHβ sequences shared approximately 92 and 93% nucleotide and amino acid sequence similarities respectively. Northern blot analysis of total cellular anterior pituitary RNA showed that an approximate 800 base transcript hybridized to a ³²P-labelled tLHβ cDNA probe.

The gonadotrophin-releasing hormone (GnRH)-and prolactin (PRL)-regulated expression of LH and PRL in dispersed pituitary cells was determined by Northern blot analysis of tLHβ and PRL steady-state mRNA levels and by RIA analysis of secreted LH and PRL. GnRH-treated cells showed increased levels of both tLHβ mRNA and secreted LH, whereas mRNA and secreted levels of PRL did not change significantly. Cells treated with PRL showed lower levels of tLHβ and PRL mRNA as well as decreased release of LH and PRL. When cells were treated with both PRL and GnRH, increases in tLHβ mRNA and secreted levels of LH observed with GnRH alone were negated, whereas the decreases in mRNA and secreted levels of PRL observed with PRL alone were abrogated.

These findings suggest that PRL can down-regulate tLHβ gene expression and spontaneous release of LH as well as autoregulate PRL gene expression and spontaneous release of PRL, while GnRH appears capable of modulating the effects of PRL-regulated LH and PRL gene expression and spontaneous release.

ABSTRACT

The present study examined turkey prolactin (PRL) transcription and PRL mRNA stability during different reproductive stages. Nuclear run-on transcription assays were performed using isolated nuclei from pituitaries of turkeys at different reproductive stages. Meanwhile, cytoplasmic PRL mRNA and plasma PRL were measured by slot blot and RIA respectively. The PRL transcription, pituitary cytoplasmic PRL mRNA abundance and plasma PRL levels increased after photostimulation and peaked at the incubating stage (P<0·05). A decrease in PRL transcription, pituitary cytoplasmic PRL mRNA and plasma PRL (P<0·05) was observed during the transition from incubation to photorefractoriness. Nest-deprivation reduced circulating PRL (P<0·05), whereas pituitary cytoplasmic PRL mRNA and PRL transcription were not significantly altered from those in incubating birds (P>0·05). The half-life of PRL mRNA was determined in pituitaries of non-photostimulated, laying, incubating and photorefractory hens. Primary pituitary cell cultures were treated with the transcription inhibitor actinomycin-D and the decay of the pre-existing PRL mRNA was quantified using Northern blot analysis. The PRL mRNA half-life was 1·5- and 1·4-fold greater in incubating and laying birds respectively than in non-photostimulated turkeys (P<0·05). The half-life of PRL mRNA in photorefractory and incubating hens was similar in spite of great differences in pituitary PRL mRNA steady-state levels and PRL transcription. Our data suggest that photoinduced changes in pituitary PRL mRNA and plasma PRL are due to changes in both PRL transcription and PRL mRNA stability. Nest-deprivation inhibits the PRL releasing mechanism(s) independently of PRL transcription in turkeys.