Transgenesis and neuroendocrine physiology: a transgenic rat model expressing growth hormone in vasopressin neurones

Abstract

Human growth hormone (hGH) and bovine neurophysin (bNP) DNA reporter fragments were inserted into the rat vasopressin (VP) and oxytocin (OT) genes in a 44 kb cosmid construct used to generate two lines of transgenic rats, termed JP17 and JP59. Both lines showed specific hGH expression in magnocellular VP cells in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). hGH was also expressed in parvocellular neurones in suprachiasmatic nuclei (SCN), medial amygdala and habenular nuclei in JP17 rats; the rat OT-bNP (rOT-bNP) transgene was not expressed in either line. Immunohistochemistry and radioimmunoassay showed hGH protein in the hypothalamus from where it was transported in varicose fibres via the median eminence to the posterior pituitary gland. Immunogold electron microscopy showed hGH co-stored with VP-NP in the same granules. The VP-hGH transgene did not affect water balance, VP storage or release in vivo. Drinking 2 % saline for 72 h increased hypothalamic transgene hGH mRNA expression, and depleted posterior pituitary hGH and VP stores in parallel. In anaesthetised, water-loaded JP17 rats, hGH was released with VP in response to an acute hypovolumic stimulus (sodium nitrosopentacyano, 400 mg I.V.). JP17 rats had a reduced growth rate, lower anterior pituitary rGH contents, and a reduced amplitude of endogenous pulsatile rGH secretion assessed by automated blood microsampling in conscious rats, consistent with a short-loop feedback of the VP-hGH on the endogenous GH axis. This transgenic rat model enables us to study physiological regulation of hypothalamic transgene protein production, transport and secretion, as well as its effects on other neuroendocrine systems in vivo.

Extrapituitary growth hormone

“…The increased hyperphagia in mice that transgenically express GH in the CNS reflects the autocrine or paracrine induction of two orexigenic hypothalamic neuropeptides, agouti-related protein, and neuropeptide Y [293]. Similarly while the systemic overexpression of bGH, results in increased body size in transgenic mice [295], the specific overexpression of human (h) GH in the cerebral cortex [296], or in hypothalamic GRF neurons [297][298][299] or in hypothalamic vasopressin neurons [300] results in dwarfism. This induction of dwarfism results from local GH actions that increase SRIF tone and decreases GRF, thereby inhibiting pituitary GH secretion.…”

Autocrine/paracrine roles of extrapituitary growth hormone and prolactin in health and disease: An overview

“…hGH expression in the GHRH neurons of the rat hypothalamus similarly increases SRIF transcription and reduces GHRH (Pellegrini et al, 1997) and similarly induces dwarfism (Flavell et al, 1996). Dwarfism is also induced in rats after hGH is expressed in the vasopressin neurons of their hypothalami (Wells et al, 2003).…”

Abnormalities of the somatotrophic axis in the obese agouti mouse

“…Radiolabelled probes were synthesised as previously described. 29 Since NPY and somatostatin are highly homologous in rats and mice, rat NPY and somatostatin riboprobes were used. The somatostatin riboprobe was a 276 base pair (bp) fragment of rat somatostatin cDNA, corresponding to nucleotides 280-556 of rat somatostatin full-length cDNA (accession number: NM_012659).…”