GnRH immunodetection in the brain of the holocephalan fish Chimaera monstrosa L.: Correlation to oocyte maturation

Dipartimento di Biologia, Università di Genova, Viale Benedetto XV 5, 16132 Genova, Italy. <>
General and Comparative Endocrinology (Impact Factor: 2.47). 06/2008; 156(3):559-63. DOI: 10.1016/j.ygcen.2008.02.016
Source: PubMed


Chimera monstrosa (rabbit fish) like other holocephalans is a rare, delicate deep sea fish. Owing to the difficulty of sampling individuals in good shape, there is a paucity of information available on the morphology and physiology of this species especially concerning reproduction. In holocephalans, a hypothalamus-pituitary-gonadal axis has been postulated and a GnRH molecule identical to cGnRH II has been identified. The aim of the present study was to correlate the presence of steroidogenic enzymes in the ovarian follicles with the presence of GnRH in the hypothalamus. Estrogens, the steroids that trigger the accumulation of yolk (vitellogenesis) in the oocytes are synthesized by the somatic cells of the follicle in the vitellogenic stages via a cascade of steroid dehydrogenases involving 3 beta-hydroxysteroid-dehydrogenase (3 beta-HSD; in the inner thecal layer) and aromatase cytochrome (P450; granulosa layer). Our results showed that 3 beta-HSD is present concomitant with the presence of cGnRH II in the preoptic area and in the ventral hypothalamus. Another form of immunoreactive GnRH, mGnRH is also present in the brain of C. monstrosa. It is localized in the ventral telencephalon and in the midbrain caudal diencephalon (boundary between ventral thalamus and tegmentum of the mesencephalon). This form of GnRH is probably correlated with sexual behaviour.

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    • "Measurements of high levels of GnRH and a possible binding protein in the serum of H. colliei suggest that the main role of GnRH is to activate the synthesis and secretion of gonadotropins from the pituitary (Pierantoni et al., 1993; Sherwood and Lovejoy, 1993). Similarly, GnRH-II has been suggested to play a role in the release of gonadotropins, since this form was present in females during follicle maturation, absent in immature females; and 3b-hydroxys- teroiddehydrogenase (3b-HSD), one of the key enzymes together with P 450 aromatase involved in the synthesis of estrogens, was present concomitant with the presence of GnRH-II (Masini et al., 2008). In fact, the GnRH-II molecule in cartilaginous fishes was found to release gonadotropin from other vertebrate groups (teleosts , birds and mammals) (Sherwood and Lovejoy, 1993). "
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    ABSTRACT: The gonadotropin-releasing hormone (GnRH) and corticotropin-releasing family (CRF) are two neuropeptides families that are strongly conserved throughout evolution. Recently, the genome of the holocephalan, Callorhinchus milii (elephant shark) has been sequenced. The phylogenetic position of C. milii, along with the relatively slow evolution of the cartilaginous fish suggests that neuropeptides in this species may resemble the earliest gnathostome forms. The genome of the elephant shark was screened, in silico, using the various conserved motifs of both the vertebrate CRF paralogs and the insect diuretic hormone sequences to identify the structure of the C. milii CRF/DH-like peptides. A similar approach was taken to identify the GnRH peptides using conserved motifs in both vertebrate and invertebrate forms. Two CRF peptides, a urotensin-1 peptide and a urocortin 3 peptide were found in the genome. There was only about 50% sequence identity between the two CRF peptides suggesting an early divergence. In addition, the urocortin 2 peptide seems to have been lost and was identified as a pseudogene in C. milii. In contrast to the number of CRF family peptides, only a GnRH-II preprohormone with the conserved mature decapeptide was found. This confirms early studies about the identity of GnRH in the Holocephali, and suggests that the Holocephali and Elasmobranchii differ with respect to GnRH structure and function.
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