Extrapituitary GH in the chicken: underestimation of immunohistochemical staining by Carnoy's fixation

Uromodulin Regulates Murine Aquaporin-2 Activity via Thick Ascending Limb-Collecting Duct Cross-Talk during Water Deprivation

Uromodulin, a urinary protein synthesized and secreted from the thick ascending limb (TAL) of the loop of Henle, is associated with hypertension through the activation of sodium reabsorption in the TAL. Uromodulin is a potential target for hypertension treatment via natriuresis. However, its biological function in epithelial cells of the distal nephron segment, particularly the collecting duct, remains unknown. Herein, we examined the regulation of uromodulin production during water deprivation in vivo as well as the effect of uromodulin on the activity of the water channel aquaporin−2 (AQP2) in vitro and in vivo using transgenic mice. Water deprivation upregulated uromodulin production; immunofluorescence experiments revealed uromodulin adhesion on the apical surface of the collecting duct. Furthermore, the activation of AQP2 was attenuated in mice lacking uromodulin. Uromodulin enhanced the phosphorylation and apical trafficking of AQP2 in mouse collecting duct cells treated with the vasopressin analog dDAVP. The uromodulin-induced apical trafficking of AQP2 was attenuated via endocytosis inhibitor treatment, suggesting that uromodulin activates AQP2 through the suppression of endocytosis. This study provides novel insights into the cross−talk between TAL and the collecting duct, and indicates that the modulation of uromodulin is a promising approach for diuresis and hypertension treatment.

Expression, cellular distribution, and heterogeneity of growth hormone in the chicken cerebellum during development

Although growth hormone (GH) is mainly synthesized and secreted by pituitary somatotrophs, it is now well established that the GH gene can be expressed in many extrapituitary tissues, including the central nervous system (CNS). Here we studied the expression of GH in the chicken cerebellum. Cerebellar GH expression was analyzed by in situ hybridization and cDNA sequencing, as well as by immunohistochemistry and confocal microscopy. GH heterogeneity was studied by Western blotting. We demonstrated that the GH gene was expressed in the chicken cerebellum and that its nucleotide sequence is closely homologous to pituitary GH cDNA. Within the cerebellum, GH mRNA is mainly expressed in Purkinje cells and in cells of the granular layer. GH-immunoreactivity (IR) is also widespread in the cerebellum and is similarly most abundant in the Purkinje and granular cells as identified by specific neuronal markers and histochemical techniques. The GH concentration in the cerebellum is age-related and higher in adult birds than in embryos and juveniles. Cerebellar GH-IR, as determined by Western blot under reducing conditions, is associated with several size variants (of 15, 23, 26, 29, 35, 45, 50, 55, 80 kDa), of which the 15 kDa isoform predominates (>30% among all developmental stages). GH receptor (GHR) mRNA and protein are also present in the cerebellum and are similarly mainly present in Purkinje and granular cells. Together, these data suggest that GH and GHR are locally expressed within the cerebellum and that this hormone may act as a local autocrine/paracrine factor during development of this neural tissue.

Extrapituitary growth hormone

Pituitary somatotrophs secrete growth hormone (GH) into the bloodstream, to act as a hormone at receptor sites in most, if not all, tissues. These endocrine actions of circulating GH are abolished after pituitary ablation or hypophysectomy, indicating its pituitary source. GH gene expression is, however, not confined to the pituitary gland, as it occurs in neural, immune, reproductive, alimentary, and respiratory tissues and in the integumentary, muscular, skeletal, and cardiovascular systems, in which GH may act locally rather than as an endocrine. These actions are likely to be involved in the proliferation and differentiation of cells and tissues prior to the ontogeny of the pituitary gland. They are also likely to complement the endocrine actions of GH and are likely to maintain them after pituitary senescence and the somatopause. Autocrine or paracrine actions of GH are, however, sometimes mediated through different signaling mechanisms to those mediating its endocrine actions and these may promote oncogenesis. Extrapituitary GH may thus be of physiological and pathophysiological significance.

Peptide hormones as developmental growth and differentiation factors

Peptide hormones, usually considered to be endocrine factors responsible for communication between tissues remotely located from each other, are increasingly being found to be synthesized in developing tissues, where they act locally. Several hormones are now known to be produced in developing tissues that are unrelated to the endocrine gland of origin in the adult. These hormones are synthesized locally, and are active as differentiation and survival factors, before the developing adult endocrine tissue becomes functional. There is increasing evidence for paracrine and/or autocrine actions for these factors during development, thus, placing them among the conventional growth and differentiation factors. We review the evidence for the view that thyroid hormones, growth hormone, prolactin, insulin, and parathyroid hormone-related protein are developmental growth and differentiation factors.

Growth hormone and its receptor in projection neurons of the chick visual system: retinofugal and tectobulbar tracts

Recent studies have shown the presence of growth hormone (GH) in the retinal ganglion cells (RGCs) of the neural retina in chick embryos at the end of the first trimester [embryonic day (E) 7] of the 21 day incubation period. In this study the presence of GH in fascicles of the optic fiber layer (OFL), formed by axons derived from the underlying RGCs, is shown. Immunoreactivity for GH is also traced through the optic nerve head, at the back of the eye, into the optic nerve, through the optic chiasm, into the optic tract and into the stratum opticum and the retinorecipient layer of the optic tectum, where the RGC axons synapse. The presence of GH immunoreactivity in the tectum occurs prior to synaptogenesis with RGC axons and thus reflects the local expression of the GH gene, especially as GH mRNA is also distributed within this tissue. The distribution of GH-immunoreactivity in the visual system of the E7 embryo is consistent with the distribution of the GH receptor (GHR), which is also expressed in the neural retina and tectum. The presence of a GH-responsive gene (GHRG-1) in these tissues also suggests that the visual system is not just a site of GH production but a site of GH action. These results support the possibility that GH acts as a local growth factor during early embryonic development of the visual system.

Expression of growth hormone and its receptor in the lungs of embryonic chicks

The lung is well established as being a postnatal target site for growth hormone (GH) action, since pathophysiological states of GH excess and deficiency are both associated with impaired pulmonary function. Pituitary GH is therefore probably involved in normal lung growth or development, although perinatal lung development occurs prior to the differentiation of pituitary somatotrophs and the ontogeny of pituitary GH secretion. The lung itself may, however, be a site of GH production during prenatal development, since a specific GH-response gene (a marker of GH activity) is expressed in the lungs of early chick embryos, in which GH immunoreactivity is widespread in many other peripheral tissues. We have assessed this possibility in embryonic chicks. A 690-bp cDNA, identical in size and nucleotide sequence to the full-length pituitary GH transcript, was amplified by reverse transcription/polymerase chain reaction from total RNA extracted from the lungs of embryos at 11, 13, 15, and 18 days of the 21-day incubation period. This transcript was localized by in situ hybridization to mesenchymal and epithelial cells of the developing lungs, in which specific GH immunoreactivity was similarly located. Intense GH immunoreactivity was also present after embryonic day 15 (ED15) in the smooth muscle surrounding blood vessels in the lung and surrounding the bronchioles. Lung GH immunoreactivity was primarily associated with a 15-kDa protein, rather than the 26-kDa protein in the pituitary gland. After the onset of pituitary GH secretion (at ED17), GH mRNA was barely detectable in the lungs of ED20 embryos, at the start of lung breathing. GH immunoreactivity was, however, still present in some cells in the lungs of ED20 embryos. GH-receptor mRNA and immunoreactivity were also widespread and abundant within the embryonic lung. Lung GH may thus have autocrine or paracrine roles in lung development or in pulmonary function prior to the ontogeny of the pituitary gland and the appearance of GH in peripheral plasma.