STRUCTURE, LOCALIZATION, AND MOLECULAR PHYLOGENY OF A GNRH CDNA FROM A PARACANTHOPTERYGIAN FISH, THE PLAINFIN MIDSHIPMAN (PORICHTHYS NOTATUS)

Multiple forms of gonadotropin releasing hormone (GnRH) are found with in several species of teleost fishes. Within the infradivision Euteleo stei, the superorder Paracanthopterygii represents one of the last maj or groups to be examined with respect to the GnRH mRNA sequence. The p lainfin midshipman, Porichthys notatus, is a common member of this sup erorder which is intermediate between the ancestral euteleost taxa and the more derived Acanthopterygians (percomorphs). The goals of this s tudy were to: (1) determine the cDNA sequence of prepro-GnRH in the pl ainfin midshipman, (2) address the anatomical localization of midshipm an prepro-GnRH gene expression, and (3) perform a cladistic analysis u sing all currently known cDNA sequences of prepro-GnRH. We report 460 base pair of cDNA sequence containing the entire protein coding region , and 5'- and 3'-untranslated regions. The deduced amino acid sequence indicates that this cDNA encodes a GnRH decapeptide identical in sequ ence to that originally isolated in salmon (Trp7, leu8 - GnRH). Northe rn analysis demonstrated transcripts in brain, ovary, and testis (600- 700 nucleotides). PCR showed that the ovarian prepro-GnRH was identica l to that found in brain. In situ hybridization labeled neurons in the ganglion of the terminal nerve and the preoptic area, forebrain areas previously observed to contain GnRH-like immunoreactivity. Last, a ph ylogenetic analysis of 18 prepro-GnRH sequences grouped the Paracantho pterygii with the Acanthopterygii. However, this recent clade was dist inct from two separate and more ancestral lineages, the Paracanthopter ygii (salmonids) and Ostariophysi (represented by catfish). (C) 1995 A cademic Press, Inc.