Sequence and distribution of pro-opiomelanocortin in the pituitary and the brain of the chicken (Gallus gallus)
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Although pro-opiomelanocortin (POMC) is a well-known hormone precursor in many species, molecular information about avian POMCs is still relatively scarce. In a former study (Berghman et al., [1998] Mol Cell Endocrinol. 142:119-130) the nucleotide and amino acid sequence of N-terminal POMC in the chicken were reported. To complete the nucleotide sequence of the precursor, rapid amplification of 3' and 5' cDNA end reactions were performed and the polymerase chain reaction (PCR) products were cloned and sequenced. The chicken POMC coding region appears to consist of 678 base pairs in the pituitary and also in the hypothalamus, as assessed by reverse transcriptase PCR. Overall nucleotide sequence homology with other species ranges from 41% (in bovine) to 57% (in rat). The distribution of the POMC mRNA in pituitary and brain was analyzed by in situ hybridization by using 33P-labelled oligonucleotides. Expression of POMC mRNA in the pituitary was restricted to the cephalic lobe, whereas in the brain, the signal was limited to the hypothalamic region. As assessed by Northern blot analysis, the length of the POMC mRNA in both the pituitary and the hypothalamus was approximately 1,200 nucleotides. By using antisera to N-terminal POMC, -melanotropin and - endorphin, POMC-containing cells were observed in the cephalic lobe of the pituitary and immunopositive perikarya were localized in the infundibular nucleus and median eminence of the hypothalamus. Immunoreactive fibers were found in the preoptic area and in the medial basal hypothalamus surrounding the third ventricle and more dorsally in the thalamus. Double-staining experiments in the pituitary clearly indicated a complete overlap of the signals generated by these antisera.
