Sequence and Distribution of Pro- Opiomelanocortin in the Pituitary and the Brain of the Chicken (Gallus gallus) HELGA H.J. GERETS, 1 * KRISTEL PEETERS, 1 LUTGARDE ARCKENS, 1 FRANS VANDESANDE, 1 AND LUC R. BERGHMAN 2 1 Laboratory of Neuroendocrinology & Immunological Biotechnology, Catholic University of Leuven, Belgium 2 Departments of Poultry Science and Veterinary Pathobiology, Texas A&M University, College Station, Texas 77843 ABSTRACT 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 polymer- ase 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 33 P-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. Immunoreac- tive 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. J. Comp. Neurol. 417:250 –262, 2000. © 2000 Wiley-Liss, Inc. Indexing terms: avian; -end; ACTH; in situ hybridization; immunocytochemistry Pro-opiomelanocortin (POMC) is the polypeptide pre- cursor of adrenocorticotropic hormone (ACTH), the opioid hormone -endorphin (-end), -lipotropin (-LPH), and -, -, and -melanotropin (-, -, -MSH) (Bertagna, 1994). These hormones are produced by proteolytic cleav- age by the prohormone convertases PC1 and PC2 in a tissue-specific manner. In the corticotropic cells of the anterior pituitary lobe, cleavage by PC1 results in ACTH and -LPH, whereas in the intermediate lobe, PC1 and PC2 act synergistically yielding -MSH and -end as the major end products (Seidah et al., 1998). In the brain, the major sites of POMC-producing neurons are located in the arcuate nucleus and adjacent regions of the medial basal hypothalamus (Pelletier et al., 1980). A second, smaller group has been detected in the nucleus tractus solitarius (Grauerholz et al., 1998). In addition, some studies also detected POMC mRNA in the amygdala, the midbrain, and the cerebral cortex, but the transcript there is only Grant sponsor: Belgian National Fund for Scientific Research; Grant sponsor: Queen Elisabeth Medical Foundation; Grant sponsor: Flemish Institute for the Advancement of Scientific and Technological Research in Industry; Grant sponsor: Fund for Scientific Research–Flanders (Belgium) (FWO); Grant number: G. 0259.96; Grant sponsor: Flemish Fund for Sci- entific Research (FWO–Vlaanderen). *Correspondence to: Helga H.J. Gerets, Laboratory of Neuroendocrinol- ogy and Immunological Biotechnology, Catholic University of Leuven, Naamsestraat 59, B-3000 Leuven, Belgium. E-mail: helga.gerets@bio.kuleuven.ac.be Received 1 April 1999; Revised 8 October 1999; Accepted 27 October 1999 THE JOURNAL OF COMPARATIVE NEUROLOGY 417:250 –262 (2000) © 2000 WILEY-LISS, INC.