GFRalpha-1 mRNAs Research Articles

Differential regulation of GDNF, neurturin, and their receptors in primary cultures of rat glial cells.

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) bind to GFR alpha-1 and GFR alpha-2 receptors, respectively, and their neurotrophic activity is mediated by the tyrosine kinase receptor, Ret. All these molecules were found to be expressed in primary cultures of rat glial cells, which were largely composed of astrocytes and maintained in serum-free medium. Although GDNF, NTN and Ret mRNA levels were at the limit of detection, RNase protection assays revealed relatively high amounts of GFR alpha-1 and GFR alpha transcripts. To characterize signals controlling their expression, glial cells were exposed to serum or treated with hormones acting through nuclear receptors and by activators of the cAMP or protein kinase C (PKC)-dependent pathways. Retinoic acid or 1,25-dihydroxyvitamin D3 appeared ineffective. In contrast, the 5-fold increase in GFR alpha-2 mRNA after 24 hr of treatment with 10(-10) M of tri-iodothyronine, suggests a physiological role of thyroid hormone in the regulation of this receptor in vivo. The serum induced a 7-fold increase in GFR alpha-1 mRNA levels. These changes may be mediated by the cAMP or PKC pathways because both forskolin and TPA up-regulated the GFR alpha-1 gene. Interestingly, only TPA led to a coordinated increase in the levels of GDNF, GFR alpha-1 and GFR alpha-2 mRNAs. On the other hand, NTN transcripts remained constant, irrespective of the culture conditions. Taken together, these results indicate that GDNF family ligands and their receptors are regulated in glial cells by common or independent transductional pathways, which could modulate their specific expression during brain development or in the case of trauma.

Regulation of GFRalpha-1 and GFRalpha-2 mRNAs in rat brain by electroconvulsive seizure.

The influence of both acute and chronic electroconvulsive seizure (ECS) or antidepressant drug treatments on expression of mRNAs encoding glial cell line-derived neurotrophic factor (GDNF) and its receptors, GFRalpha-1, GFRalpha-2, and c-Ret proto-oncogene (RET) in the rat hippocampus was examined by in situ hybridization. Two hours after acute ECS, levels of GFRalpha-1 mRNA in the dentate gyrus were significantly increased. This increase peaked to nearly 3-fold at 6 h after acute ECS and returned to basal levels 24 h after treatment. Chronic (once daily for 10 days) ECS significantly increased the expression of GFRalpha-1 mRNA nearly 5-fold after the last treatment. Levels of GFRalpha-2 mRNA in the dentate gyrus were also significantly increased by acute and chronic ECS, although this effect was less than that observed for GFRalpha-1. Maximum induction of GFRalpha-2 was 30% and 70% compared to sham in response to acute or chronic ECS, respectively. Levels of GDNF and RET mRNAs were not significantly changed following either acute or chronic ECS treatment at the time points examined. Chronic (14 days) administration of different classes of antidepressant drugs, including tranylcypromine, desipramine, or fluoxetine, did not significantly affect the GDNF, GFRalpha-1, GFRalpha-2, or RET mRNA levels in CA1, CA3, and dentate gyrus areas of hippocampus. The results demonstrate that acute ECS increases the expression of GFRalpha-1 and GFRalpha-2 and that these effects are enhanced by chronic ECS. The results also imply that regulation of the binding components of GDNF receptor complex may mediate the adaptive responses of the GDNF system to acute and chronic stimulation.

Expression of GFR alpha-1, GFR alpha-2, and c-Ret mRNAs in rat adrenal gland.

Glial cell line-derived neurotrophic factor (GDNF), an important factor for developing and lesioned pre- and postganglionic sympathetic neurons, and its congeners signal through a receptor complex consisting of the tyrosine kinase c-Ret and a lipid-anchored alpha receptor (GFR alpha 1-4). Using in situ hybridization we show now that the mRNA for GFR alpha-2 is abundant in the adult rat adrenal medulla and its chromaffin cells. Coexpression of c-Ret and GFR alpha-1 mRNA's is restricted to a scarce subpopulation of medullary sympathetic neurons. Both GFR alpha-1 and GFR alpha-2 mRNA's are associated with preganglionic nerve trunks in the adrenal cortex. It is conceivable therefore that GDNF and related factors may activate chromaffin and preganglionic Schwann cells through a GFR-alpha receptor in absence of c-Ret.

GFRalpha-3, a protein related to GFRalpha-1, is expressed in developing peripheral neurons and ensheathing cells.

We report here the identification of a gene, termed GFRalpha-3 (glial cell line-derived neurotrophic factor family receptor alpha-3), related to GFRalpha-1 and GFRalpha-2 (also known as GDNFR-alpha and GDNFR-beta), and describe distribution of GDNFalpha-3 in the nervous system and other parts of the mouse body during development and in the adult. GFRalpha-3 in situ hybridization signals were found mainly in the peripheral nervous system, with prominent signals in developing dorsal root and trigeminal ganglia. Sympathetic ganglia were also positive. Developing nerves manifested strong GFRalpha-3 mRNA signals, presumably generated by the Schwann cells. Olfactory ensheathing cells were also positive. Other non-neuronal cells appearing positive during development included chromaffin cells in the adrenal gland and small clusters of cells in the intestinal epithelium. In the central nervous system no robust signals could be detected at any stage investigated with the present probes. Compared with the previously described GFRalpha-1 and GFRalpha-2 mRNAs, which are widely distributed in the central nervous system and peripheral organs, the expression of GFRalpha-3 mRNA is much more restricted. The prominent expression in Schwann cells during development suggests a key role for GFRalpha-3 in the development of the peripheral nervous system. As Schwann cells are known to lack expression of the transducing RET receptor, we propose that a possible function of GFRalpha-3 during development could be to bind Schwann cell-derived GDNF-like ligands, thus presenting such molecules to growing axons.

Expression of GDNF and its receptors in developing tooth is developmentally regulated and suggests multiple roles in innervation and organogenesis.

Glial cell line-derived neurotrophic factor (GDNF) is a recently identified survival factor for several populations of neurons in the central and peripheral nervous system that also regulates kidney development. To study the roles of GDNF in the regulation of tooth innervation and formation, we analyzed by in situ hybridization the expression patterns of GDNF and its receptors Ret, GDNF family receptor alpha-1 (GFRalpha-1), and GFRalpha-2 from the initiation of first molar formation to the completion of crown morphogenesis. At the time of trigeminal axon ingrowth, GDNF mRNAs were expressed in the mesenchyme around the tooth germ (i.e., target field of the dental innervation), suggesting that it is involved in the regulation of the embryonic tooth innervation. This hypothesis was supported by the ability of GDNF to induce neurite outgrowth from embryonic day 12 (E12) to E15 trigeminal ganglia. This timing correlated with the appearance of Ret in the subset of cells in the trigeminal ganglion at E12, whereas GFRalpha-1 and GFRalpha-2 receptors were constantly expressed in trigeminal ganglion during E11-E15. After birth, GDNF expression showed apparent correlation with the ingrowth and presence of trigeminal nerve fibers in the tooth, suggesting that GDNF is involved in the regulation of innervation of the dental papilla and dentin postnatally. Ret, GFRalpha-1, and GFRalpha-2 mRNAs were expressed in the dental epithelial and mesenchymal cells at stages when epithelial-mesenchymal signalling regulates critical steps of tooth morphogenesis. Ret and GFRalpha-2 were colocalized in the dental mesenchyme during bud and cap stages. Expression of GFRalpha-1 associated with the formation of the epithelial enamel knot, which is a putative embryonic signalling center regulating tooth shape. During postnatal development, GDNF and its receptors were expressed in dental papilla mesenchyme. In addition, GDNF and GFRalpha-1 transcripts were seen in the preodontoblasts and odontoblasts, suggesting that they may be involved in differentiation and maintenance of functional properties of the odontoblasts. Taken together, these results suggest that GDNF acts as a target-derived neurotrophic factor during tooth innervation. In addition, GDNF and its receptors may have nonneuronal organogenetic functions during tooth morphogenesis.