Phylogenetic considerations on GnRH precursors in vertebrates.

GUSTAVO M. SOMOZA; LEONARDO G. GUILGUR; PABLO H. STROBL-MAZZULLA; LEANDRO A. MIRANDA

Faro

Congreso; V Congreso Associación Ibérica de Endocrinologia Comparada.; 2005

Associación Ibérica de Endocrinologia Comparada.

Until now, a total of 14 GnRH structural variants have been isolated and characterized from vertebrate nervous tissue, however other GnRH forms have been characterized in protochordates and invertebrates. All vertebrate species have at least two GnRH forms coexisting in the central nervous system. However, it is now well accepted that three forms of GnRH are present in early and late evolved bony fishes. In these cases, cGnRH-II is expressed by midbrain neurons, a species-specific GnRH is present mainly in the preoptic area and the hypothalamus, and sGnRH is mainly localized in the terminal nerve ganglion (TNG). In this context it was possible to think that at least three GnRH receptors (GnRH-R) subtypes are expressed in the central nervous system. Then three different GnRH lineages expressed by distinct brain areas: (1) the conserved cGnRH-II or mesencephalic lineage; (2) the hypothalamic or “releasing” lineage whose primary structure has diverged by point mutations (mGnRH and its orthologous forms: hrGnRH, wfGnRH, cfGnRH, sbGnRH, and pjGnRH); and (3) the telencephalic sGnRH form only found in teleosts. The cDNAs encoding to the preprohormone corresponding to these GnRH variants have also been cloned in a number of species allowing sequence comparisons in order to understand phylogenetic relationships between these different variants. Despite the fact that some reports suggested the presence of a third GnRH form in tetrapods, up to now there is no clear demonstration of this fact. Then, is the presence of three GnRH variants in vertebrates a rule?