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Localisation of insulin-like growth factor I (igf1)in the hypothalamic-pituitary-gonadal (HPG) axis of developing and adult male and female bony fish, the tilapia (Orechromis niloticus) - Zurich Open Repository and Archive


Moret, O D. Localisation of insulin-like growth factor I (igf1)in the hypothalamic-pituitary-gonadal (HPG) axis of developing and adult male and female bony fish, the tilapia (Orechromis niloticus). 2011, University of Zurich, Faculty of Medicine.

Abstract

Pituitary adenomas are the third most frequent primary intracranial neoplasms. Excess pituitary hormone secretion is proposed to arise from one specific progenitor cell with a selective survival advantage. Thus, hormones involved in cell proliferation, maintenance and apoptosis are considered especially relevant. This demands for better knowledge on factors potentially influencing pituitary development and cell differentiation. For instance, human non-functioning pituitary adenomas have been found to secrete diverse growth factors including insulin-like growth factor I (igf1), a potent hormone that stimulates growth and differentiation, especially during development, and inhibits apoptosis. The major source of circulating igf1 originates from the liver, but igf1-producing cells also occur in other organs including the pituitary. Igf1 is released under the control of pituitary GH, the main regulator of growth, maintenance and development. The amount of circulating igf1 regulates synthesis and release of GH via a negative feed-back mechanism in mammals. However, our knowledge on the presence of igf1 in the pituitary is limited. Additionally, only few data exist on the role of igf1 in fish reproduction, a topic which is of emerging relevance in the light of world-wide decline of fish populations. Thus, as a model, we localized the igf1 gene expression at different levels of the hypothalamic-pituitary-gonadal (HPG) axis of a representative bony fish, the tilapia (Oreochromis niloticus) by in situ hybridisation. For that purpose, hypothalamus, pituitary and gonads of monosex breedings of male and female tilapia were investigated from 0 day post fertilization (DPF) to adulthood. Igf1 mRNA was detected in neuronal perikarya within the hypothalamus. At the pituitary level, igf1 gene expression was mainly restricted to the adenohypophysis where igf1 mRNA was first detected at 30 DPF in some cells of the ACTH, α-MSH and GH regions. Around 30 DPF, igf1 mRNA appeared in cells in the gonadotrophin (GTH) regions of the female and at 50 DPF of the male pituitary. During puberty (around 80 DPF), the expression of igf1 mRNA in GTH cells was most pronounced in both sexes. It is assumed that igf1 released from the GTH cells acts as auto/paracrine regulator of cell proliferation and enhances GTH synthesis and release during puberty and reproductive phases. Also in adult adenohypophysis, igf1 mRNA was present in the majority of ACTH cells in all individuals investigated. Igf1 mRNA was further observed in GH cells with pronounced inter-individual differences likely due to the physiological, e.g., nutritional, status of the individual. Igf1 released from the GH cells may serve as auto/paracrine mediator of a negative feedback mechanism in addition to liver-derived endocrine igf1.
In the male and female gonad anlage, igf1 mRNA appeared in somatic cells at 7 DPF. In female germ cells igf1 mRNA was found at 29 DPF and in male germ cells at 51-53 DPF, suggesting that the production of igf1 in the germ cells is linked to the onset of meiosis, indicating a specific role for igf1 in the regulation of cell differentiation and reproduction. In summary, ifg1 seems to play a crucial role at different levels of the HPG axis. The study serves as a basis for further studies to investigate how far igf1 locally regulates organ development, endocrine cell proliferation, hormone synthesis and release within the pituitary.

Abstract

Pituitary adenomas are the third most frequent primary intracranial neoplasms. Excess pituitary hormone secretion is proposed to arise from one specific progenitor cell with a selective survival advantage. Thus, hormones involved in cell proliferation, maintenance and apoptosis are considered especially relevant. This demands for better knowledge on factors potentially influencing pituitary development and cell differentiation. For instance, human non-functioning pituitary adenomas have been found to secrete diverse growth factors including insulin-like growth factor I (igf1), a potent hormone that stimulates growth and differentiation, especially during development, and inhibits apoptosis. The major source of circulating igf1 originates from the liver, but igf1-producing cells also occur in other organs including the pituitary. Igf1 is released under the control of pituitary GH, the main regulator of growth, maintenance and development. The amount of circulating igf1 regulates synthesis and release of GH via a negative feed-back mechanism in mammals. However, our knowledge on the presence of igf1 in the pituitary is limited. Additionally, only few data exist on the role of igf1 in fish reproduction, a topic which is of emerging relevance in the light of world-wide decline of fish populations. Thus, as a model, we localized the igf1 gene expression at different levels of the hypothalamic-pituitary-gonadal (HPG) axis of a representative bony fish, the tilapia (Oreochromis niloticus) by in situ hybridisation. For that purpose, hypothalamus, pituitary and gonads of monosex breedings of male and female tilapia were investigated from 0 day post fertilization (DPF) to adulthood. Igf1 mRNA was detected in neuronal perikarya within the hypothalamus. At the pituitary level, igf1 gene expression was mainly restricted to the adenohypophysis where igf1 mRNA was first detected at 30 DPF in some cells of the ACTH, α-MSH and GH regions. Around 30 DPF, igf1 mRNA appeared in cells in the gonadotrophin (GTH) regions of the female and at 50 DPF of the male pituitary. During puberty (around 80 DPF), the expression of igf1 mRNA in GTH cells was most pronounced in both sexes. It is assumed that igf1 released from the GTH cells acts as auto/paracrine regulator of cell proliferation and enhances GTH synthesis and release during puberty and reproductive phases. Also in adult adenohypophysis, igf1 mRNA was present in the majority of ACTH cells in all individuals investigated. Igf1 mRNA was further observed in GH cells with pronounced inter-individual differences likely due to the physiological, e.g., nutritional, status of the individual. Igf1 released from the GH cells may serve as auto/paracrine mediator of a negative feedback mechanism in addition to liver-derived endocrine igf1.
In the male and female gonad anlage, igf1 mRNA appeared in somatic cells at 7 DPF. In female germ cells igf1 mRNA was found at 29 DPF and in male germ cells at 51-53 DPF, suggesting that the production of igf1 in the germ cells is linked to the onset of meiosis, indicating a specific role for igf1 in the regulation of cell differentiation and reproduction. In summary, ifg1 seems to play a crucial role at different levels of the HPG axis. The study serves as a basis for further studies to investigate how far igf1 locally regulates organ development, endocrine cell proliferation, hormone synthesis and release within the pituitary.

Additional indexing

Item Type:Dissertation
Referees:Eppler E, Ullrich O
Communities & Collections:04 Faculty of Medicine > Institute of Anatomy
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2011
Deposited On:06 Mar 2012 12:41
Last Modified:05 Apr 2016 15:38
Number of Pages:32
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&CON_LNG=GER&func=find-b&find_code=SYS&request=006556618

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