Differential neuronal expression and projections of melanin-concentrating hormone (MCH) and MCH-gene-overprinted-polypeptide (MGOP) in the rat brain

The rat melanin-concentrating hormone (MCH) gene may produce, through alter native splicing, either the precursor of MCH and neuropeptide EI, two neuro peptides coexpressed in the zona incerta (ZI) and lateral hypothalamus (LHA ), or a putative protein we named previously MCH-gene-overprinted-polypepti de (MGOP). First, we investigated the distribution and relative expression of MCH and MGOP mRNA in the rat brain by Northern blotting, RT-PCR and in s itu hybridization. MGOP gene transcripts were detected mainly in the hypoth alamus only by RT-PCR. Second, different antisera were raised toward the C- terminus of MGOP and used to identify the translational products. In the ra t brain, no MGOP-processed peptide could be detected based on RP-HPLC coupl ed to specific RIA. A polypeptide of 14 kDa was found in the secretory path way of transfected monkey COS7 cells expressing recombinant MGOP. In the ra t hypothalamus, a specific protein of 12 kDa was identified by Western blot analysis. Finally, distribution of MGOP-immunoreactivity (IR) was investig ated in the rat brain. Colocalization studies demonstrated that 98% of the MGOP-expressing perikarya in ZI/LHA also synthesized MCH. In addition, nume rous, strongly stained MGOP-containing neurons were encountered in the hypo thalamic periventricular nucleus. Perikarya labelled with MGOP antiserum we re also found scattered in the cortex, caudate putamen, amygdala and latera l septal nucleus. MCH was not detected in these MGOP-containing neurons. St rikingly, dense staining of terminals was observed with MGOP antiserum but not with MCH antibodies in the suprachiasmatic, ventromedial and arcuate nu clei, and also in the external layer of the median eminence. These results demonstrated that MGOP and MCH-IR overlapped in LHA/ZI but displayed a diff erential distribution in other areas. Based on this cerebral distribution, MGOP may act as a new secreted protein in regulating many neuroendocrine fu nctions, such as nursing, feeding and growth control in associated behaviou ral components.