DEVELOPMENTAL AND STAGE-DEPENDENT EXPRESSION OF MELANIN-CONCENTRATINGHORMONE IN MAMMALIAN GERM-CELLS

Melanin-concentrating hormone (NIGH) is a cyclic peptide predominantly expressed in the hypothalamus of mammals. This peptide modulates the stress response and regulates many goal-oriented behaviors in the rat brain. MCH mRNA and peptides generated from the precursor, namely MCH and neuropeptide (N) glutamic acid (E) isoleucine (I) amide (NEI), wer e also found in rodent peripheral tissues including those in adult tes tis. In the present study, we first examined the cellular distribution and content of MCH gene products and peptide in the testes of adult r ats. Using reverse-transcription polymerase chain reaction with MCH ge ne primers and in situ hybridization with specific P-33-labeled oligop robes, we characterized the MCH RNA species. Pro-MCH products were rev ealed through use of immunoperoxidase detection and an RIA with specif ic MCH and NEI antisera. Both MCH gene transcripts and MCH peptide wer e found within germ cells at the periphery of some of the seminiferous tubules of adult rats. We further investigated temporal expression of MCH in 7-mu m sections of testes from adult rats and mice. MCH was pr edominantly found in nuclei of spermatogonia at stages II-IV of sperma togenesis and in nuclei of leptotene and zygotene spermatocytes (at st ages IX-XIII). MCH was markedly absent in preleptotene spermatocytes a t the stage VII-VIII, and MCH immunoreactivity was no longer detectabl e as spermatocytes underwent the pachytene step. MCH immunoreactivity was also found in some peritubular cells, mainly at stages II-IV. Fina lly, we studied MCH expression during puberty in the rat, in sterile m utant mice, and in one adult man. We found predominant staining with M CH antiserum over nuclei of immature germ cells as early as 10 days po stpartum in the rat and further confirmed the absence of staining exce pt for that in spermatogonia and early spermatocytes during rat postna tal development. MCH distribution was found to be similar in normal an d sterile mutant mice, suggesting that MCH expression is not dependent upon the early steps of spermiogenesis. MCH immunoreactivity was foun d to be confined to the nuclei of spermatogonia and early spermatocyte s in the adult man. Our results indicate that MCH is present predomina ntly within nuclei of spermatogonia and primary spermatocytes in three mammalian species and that its expression is under strong stage-speci fic and developmental regulation. This peptide may play a role during stem cell renewal and/or differentiation of early spermatocytes.