ISOLATION, CHARACTERIZATION AND EXPRESSION OF CDNAS ENCODING THE CATFISH-TYPE AND CHICKEN-II-TYPE GONADOTROPIN-RELEASING-HORMONE PRECURSORSIN THE AFRICAN CATFISH

The cDNAs encoding the catfish prepro-gonadotropin-releasing hormone a nd the chicken prepro-gonadotropin-releasing hormone II of the African catfish (Clarias gariepinus) have been isolated and sequenced. The ca tfish gonadotropin-releasing-hormone precursor and the chicken gonadot ropin-releasing-hormone-II precursor have the same overall architectur e as other gonadotropin-releasing-hormone precursors identified so far ; each is composed of a signal peptide, gonadotropin-releasing hormone and a gonadotropin-releasing-hormone-associated peptide which is conn ected to gonadotropin-releasing hormone by a Gly-Lys-Arg sequence. The amino acid sequences of catfish gonadotropin-releasing hormone and ch icken gonadotropin-releasing hormone II, in combination with the Gly-L ys-Arg sequence, are highly conserved during evolution when compared w ith the corresponding regions of mammalian, avian (chicken gonadotropi n-releasing hormone I) and other fish gonadotropin-releasing-hormone p recursors. However, the gonadotropin-releasing-hormone-associated pept ide regions are markedly divergent. Northern-blot analysis revealed th e presence of a single catfish gonadotropin-releasing-hormone mRNA spe cies of about 470 bases, and the presence of a single chicken gonadotr opin-releasing-hormone-II mRNA species of about 650 bases in the Afric an catfish brain. In situ hybridization revealed catfish gonadotropin- releasing-hormone cell bodies rostro-caudally scattered in the olfacto ry nerve, along both sides of the midline of the telencephalon, in the preoptic area of the ventral hypothalamus, and in the infundibular st alk close to the pituitary. Chicken gonadotropin-releasing-hormone-II cell bodies, however, were exclusively found in the midbrain tegmentum .