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Insulin-like growth factor I (IGF-I) in the hypothalamic-pituitary-gonadal (HPG) axis during development of male and female tilapia, Oreochromis niloticus

Moret O., Berishvili G., Shved N., Eppler E., D'Cotta H., Baroiller J.F., Reinecke M.. 2008. Cybium, 32 (2) : p. 31-33.

IGF-I plays a crucial role in the regulation of bony fish growth, differentiation, and reproduction. The major source of circulating IGF-I is liver, but IGF-I-producing cells also occur in other organs. Our knowledge on the presence of IGF-I in the hypothalamic-pituitary-gonadal (HPG) axis is limited. Thus, hypothalamus, pituitary and gonads of monosex breedings of male and female tilapia from 0 day post fertilization (DPF) to adulthood were investigated for the occurrence of IGF-I mRNA by in situ hybridization. In the male and female gonad anlage, IGF-I mRNA appeared in somatic cells at 7 DPF In female germ cells IGF-I mRNA was found at 29 DPF, and in male germ cells at 51-53 DPF suggesting that the production of IGF-I in the germ cells is linked to the onset of meiosis. In the neurohypophysis, axons containing IGF-I-immunoreactivity appeared around 17 DPF but no IGF-I mRNA was detected suggesting that IGF-I mRNA containing neuronal perikarya within the hypothalamus are the source. In the adenopituitary, IGF-I mRNA was first detected at 30 DPF in some cells of the ACTH, [alpha]-MSH and GH regions and persisted throughout life constitutively in ACTH and [alpha]-MSH cells but its presence in GH cells showed marked inter-individual differences in later life, the latter likely due to the physiological status of the individual. Around 30 DPF, IGF-I mRNA appeared in cells in the gonadotropin (GTH) regions of the female and at 50 DPF of the male pituitary. During puberty (around 80 DPF), the expression of IGF-I mRNA in GTH cells was most pronounced in both sexes. It is assumed that IGF-I released from the GTH cells acts as auto/paracrine regulator of cell proliferation and enhances GTH synthesis and release during puberty and reproductive phases. (Résumé d'auteur)

Mots-clés : maturité sexuelle; détermination du sexe; différenciation sexuelle; hormone adrénocorticotrope; facteur de croissance igf; gonadotrophine; oreochromis niloticus

Thématique : Production de l'aquaculture

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