GFRalpha-4, a new GDNF family receptor

Analysis of the retrograde transport of glial cell line-derived neurotrophic factor (GDNF), neurturin, and persephin suggests that in vivo signaling for the GDNF family is GFRalpha coreceptor-specific

Neurturin (NRTN) and glial cell line-derived neurotrophic factor (GDNF) are members of a family of trophic factors with similar actions in vitro on certain neuronal classes. Retrograde transport of GDNF and NRTN was compared in peripheral sensory, sympathetic, and motor neurons to determine whether in vivo these factors are transported selectively by different neuronal populations. After sciatic nerve injections, NRTN was transported by sensory neurons of the dorsal root ganglion (DRG). Competition studies demonstrated only limited cross-competition between NRTN and GDNF, indicating selective receptor-mediated transport of these factors. By using immunohistochemistry, we identified two populations of NRTN-transporting DRG neurons: a major population of small, RET-positive, IB4-positive, non-TrkA-expressing neurons that also show the ability to transport GDNF and a minor population of calretinin-expressing neurons that fail to transport GDNF. Spinal motor neurons in the adult showed relatively less ability to transport NRTN than to transport GDNF, although NRTN prevented the cell death of neonatal motor neurons in a manner very similar to GDNF (Yan et al., 1995) and persephin (PSPN) (Milbrandt et al., 1998). Last, NRTN, like GDNF, was not transported to sympathetic neurons of the adult superior cervical ganglion (SCG) after injection into the anterior eye chamber. These data reveal a high degree of functional selectivity of GDNF family receptor-alpha (GFRalpha) coreceptor subtypes for NRTN and GDNF in vivo.

Receptors of the glial cell line-derived neurotrophic factor family of neurotrophic factors signal cell survival through the phosphatidylinositol 3-kinase pathway in spinal cord motoneurons

The members of the glial cell line-derived neurotrophic factor (GDNF) family of neurotrophic factors (GDNF, neurturin, persephin, and artemin) are able to promote in vivo and in vitro survival of different neuronal populations, including spinal cord motoneurons. These factors signal via multicomponent receptors that consist of the Ret receptor tyrosine kinase plus a member of the GDNF family receptor alpha (GRFalpha) family of glycosylphosphatidylinositol-linked coreceptors. Activation of the receptor induces Ret phosphorylation that leads the survival-promoting effects. Ret phosphorylation causes the activation of several intracellular pathways, but the biological effects caused by the activation of each of these pathways are still unknown. In the present work, we describe the ability of the GDNF family members to promote chicken motoneuron survival in culture. We show the presence of Ret and GFRalpha-1, GFRalpha-2, and GFRalpha-4 in chicken motoneurons using in situ hybridization and reverse transcription-PCR techniques. By Western blot analysis and kinase assays, we demonstrate the ability of these factors to induce the phosphatidylinositol 3 kinase (PI 3-kinase) and the extracellular regulated kinase (ERK)-mitogen-activated protein (MAP) kinase pathways activation. To characterize the involvement of these pathways in the survival effect, we used the PI 3-kinase inhibitor LY 294002 and the MAP kinase and ERK kinase (MEK) inhibitor PD 98059. We demonstrate that LY 294002, but not PD 98059, prevents GDNF-, neurturin-, and persephin-induced motoneuron survival, suggesting that PI 3-kinase intracellular pathway is responsible in mediating the neurotrophic effect.

Localization of GDNF/neurturin receptor (c-ret, GFRalpha-1 and alpha-2) mRNAs in postnatal rat brain: differential regional and temporal expression in hippocampus, cortex and cerebellum

Recent studies have identified a multi-component receptor system for the neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF) and its homolog, neurturin (NTN), comprising the signaling tyrosine kinase, Ret and multiple GPI-linked binding proteins, GDNF family receptor alpha-1 and alpha-2 (GFRalpha-1 and GFRalpha-2). In the present study the localization of c-ret and GFRalpha-1 and GFRalpha-2 mRNAs was assessed in the developing rat brain from postnatal day 4 to 70 by in situ hybridization histochemistry, using specific [35S]-labeled oligonucleotides. GFRalpha-1 and GFRalpha-2 mRNAs were differentially distributed throughout the brain at all ages studied, particularly in cerebral cortex, hippocampus, substantia nigra and regions of the thalamus and hypothalamus - both distributions overlapping but different to that of c-ret mRNA. C-ret mRNA was abundant in areas such as the lateral habenula, reticular thalamic nucleus, substantia nigra pars compacta, cranial motor nuclei, and the Purkinje cell layer of the cerebellum. GFRalpha-1 mRNA was abundant in dorsal endopiriform nucleus, medial habenula, reticular thalamic nucleus, pyramidal and granule cell layers of the hippocampus, substantia nigra pars compacta and in cranial motor nuclei. GFRalpha-2 mRNA was highly expressed in many regions including olfactory bulb, lateral olfactory tract nucleus, neocortical layers IV and VI, septum, zona incerta, and arcuate and interpeduncular nuclei. GFRalpha-2 mRNA was detected in the pyramidal cell layers (CA3) of hippocampus at P4 and P7, but was no longer detectable at P14 and beyond, including P70 (adult). GFRalpha-2 mRNA was also detected in Purkinje cells throughout the cerebellum in young postnatal rats, but was enriched in the posterior lobes at P28 and P70. These localization studies support evidence of GDNF/NTN as target-derived and autocrine/paracrine trophic factors in developing brain pathways and earlier suggestions of unique and complex signaling mechanisms for these factors via a family of receptors. Strong expression of GFRalpha-1 and GFRalpha-2 mRNAs in adult brain suggests possible non-trophic functions of GDNF/NTN, as described for other neurotrophins, such as brain-derived neurotrophic factor.

Multiple actions of neurturin correlate with spatiotemporal patterns of Ret expression in developing chick cranial ganglion neurons

The neurotrophic effects of neurturin (NRTN) on chick cranial ganglia were evaluated at various embryonic stages in vitro and related to its receptor expression. NRTN promoted the outgrowth and survival of ciliary ganglion neurons at early embryonic (E) stages (E6-E12), trigeminal ganglion neurons at midstages (E9-E16), and vestibular ganglion neurons at late stages (E12-E16). NRTN had no positive effects on cochlear ganglion neurons throughout development. In accordance with the time and order of onset in NRTN responsiveness, Ret protein was first detected in ciliary ganglia at E6, subsequently in trigeminal ganglia at E9, and in vestibular ganglia at E12. Ret was absent in E16 ciliary ganglia as well as in cochlear ganglia at all developmental stages that were tested. Exogenous application of retinoic acid induced NRTN responsiveness and Ret protein expression from E9 vestibular ganglion neurons, suggesting that retinoic acid can regulate Ret protein expression in peripheral sensory neurons in vitro. Ret was confined to the neuron cell body, whereas GFRalpha was localized predominantly in peripheral and central neurite processes. No noticeable change in GFRalpha expression was seen in any cranial ganglia throughout the developmental stages that were tested (E6-E16). These results demonstrate that NRTN exerts neurotrophic effects on different cranial ganglia at different developmental stages and that the onset and offset of NRTN responsiveness are regulated mainly by the spatiotemporal patterns of Ret, but not of GFRalpha receptors. The results also substantiate the recently emerging view that NRTN may be an essential target-derived neurotrophic factor for parasympathetic neurons during development.

Expression of neurturin, GDNF, and GDNF family-receptor mRNA in the developing and mature mouse

The GDNF family of neurotrophic factors currently has four members: neurturin (NRTN), glial cell line-derived neurotrophic factor (GDNF), persephin, and artemin. These proteins are potent survival factors for several populations of central and peripheral neurons. The receptors for these factors are complexes that include the Ret tyrosine kinase receptor and a GPI-linked, ligand-binding component called GDNF family receptor alpha 1-4 (GFRalpha1-4). We have used in situ hybridization to study the mRNA expression of NRTN, GDNF, Ret, GFRalpha1, and GFRalpha2 during embryonic development and in the adult mouse. GDNF receptors were prominently expressed during embryonic development in the nervous system, the urogenital system, the digestive system, the respiratory system, and in developing skin, bone, muscle, and endocrine glands. In some regions, incomplete receptor complexes were expressed suggesting that other, as yet unidentified, receptor components exist or that receptor complexes are formed in trans. NRTN and GDNF were expressed in many trigeminal targets during embryonic development including the nasal epithelium, the teeth, and the whisker follicles. NRTN and GDNF were also expressed in the developing limbs and urogenital system. In the embryo, GDNF factors and receptors were expressed at several sites of mesenchyme/epithelial induction, including the kidney, tooth, and submandibular gland. This expression pattern is consistent with the possibility that the GDNF factors function in inductive processes during embryonic development and with the recently discovered role of NRTN as a necessary trophic factor for the development of some parasympathetic neurons. In the mature animal, receptor expression was more limited than in the embryo. In the adult mouse, NRTN was most prominently expressed in the gut, prostate testicle, and oviduct; GDNF was most prominently expressed in the ovary.

Differential effects of glial cell line-derived neurotrophic factor and neurturin on developing and adult substantia nigra dopaminergic neurons

Neurturin (NTN) and glial cell line-derived neurotrophic factor (GDNF), two members of the GDNF family of growth factors, exert very similar biological activities in different systems, including the substantia nigra. Our goal in the present work was to compare their function and define whether nonoverlapping biological activities on midbrain dopaminergic neurons exist. We first found that NTN and GDNF are differentially regulated during postnatal development. NTN mRNA progressively decreased in the ventral mesencephalon and progressively increased in the striatum, coincident with a decrease in GDNF mRNA expression. This finding suggested distinct physiological roles for each factor in the nigrostriatal system. We therefore examined their function in ventral mesencephalon cultures and found that NTN promoted survival comparable with GDNF, but only GDNF induced sprouting and hypertrophy of developing dopaminergic neurons. We subsequently examined the ability of NTN to prevent the 6-hydroxydopamine-induced degeneration of adult dopaminergic neurons in vivo. Fibroblasts genetically engineered to deliver high levels of GDNF or NTN were grafted supranigrally. NTN was found to be as potent as GDNF at preventing the death of nigral dopaminergic neurons, but only GDNF induced tyrosine hydroxylase staining, sprouting, or hypertrophy of dopaminergic neurons. In conclusion, our results show selective survival-promoting effects of NTN over wider survival, neuritogenic, and hypertrophic effects of GDNF on dopaminergic neurons in vitro and in vivo. Such differences are likely to underlie unique roles for each factor in postnatal development and may ultimately be exploited in the treatment of Parkinson's disease.

A rapid and dynamic regulation of GDNF-family ligands and receptors correlate with the developmental dependency of cutaneous sensory innervation

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) are members of the transforming growth factor-beta family and have been shown to elicit neurotrophic effects upon several classes of neurons including dopaminergic neurons, motoneurons, parasympathetic, sympathetic as well as primary sensory neurons. However, there is little information available on their roles in cutaneous innervation. Herein, we have studied the regulation of gdnf, ntn and the GDNF family receptors and examined their role in the development of facial cutaneous innervation in GDNF mutant mice. A dynamic spatial and temporal regulation of gdnf, ntn and their ligand binding receptors within the follicle-sinus complex correlate with development of distinct subclasses of sensory nerve endings. Furthermore, development of NGF-dependent myelinated mechanoreceptors, i.e. reticular and transverse lanceolate endings also require GDNF during ending formation and maintenance. In addition, ligand and receptor association seems to be intricately linked to a local Schwann cell-axon interaction essential for sensory terminal formation. Our results suggests that functionally specified nerve endings depend on different GDNF family members and that in contrast to neurotrophins, this family of neurotrophic factors may be acting at local sites of terminal Schwann cell-axon growth cone interactions and that they collaborate with neurotrophins by supporting the same populations of neurons but at different times in development.

Differences and developmental changes in the responsiveness of PNS neurons to GDNF and neurturin

We have studied the ability of GDNF and neurturin to promote the in vitro survival of populations of embryonic chicken parasympathetic, sympathetic, and sensory neurons. We show that these neurons are more responsive to one or other of these factors at particular stages of development. Whereas the parasympathetic neurons are more sensitive to neurturin at late embryonic stages, sympathetic neurons are more sensitive to neurturin at early stages. In contrast, sensory neurons of the nodose ganglion are more sensitive to GDNF throughout embryonic development. Using competitive RT/PCR, we measured the levels of mRNAs encoding GDNF and neurturin receptors in purified neurons. All neurons expressed Ret mRNA, which encodes the common receptor tyrosine kinase for GDNF and neurturin. Neurons that were more sensitive to GDNF expressed higher levels of GFRalpha-1 mRNA than GFRalpha-2 mRNA and neurons that were more sensitive to neurturin expressed higher levels of GFRalpha-2 mRNA than GFRalpha-1 mRNA. These results show that populations of PNS neurons differ markedly in their responsiveness to GDNF and neurturin at certain stages of the development and suggest that these differences are governed in part by the relative levels of expression of members of the GFRalpha family of GPI-linked receptors.

Hirschsprung disease and other enteric dysganglionoses

Hirschsprung disease has become a paradigm for multigene disorders because the same basic phenotype is associated with mutations in at least seven distinct genes. As such, the condition poses distinct challenges for clinicians, patients, diagnostic pathologists, and basic scientists, who must cope with the implications of this genetic complexity to comprehend the pathogenesis of the disorder and effectively manage patients. This review focuses on the anatomic pathology, genetics, and pathogenesis of Hirschsprung disease and related conditions. The nature and functions of "Hirschsprung disease genes" are examined in detail and emphasis is placed on the importance of animal models to this field. Where possible, potential uses and limitations of new data concerning molecular genetics and pathogenesis are discussed as they relate to contemporary medical practices.

Other neurotrophic factors: glial cell line-derived neurotrophic factor (GDNF)

Glial cell line-derived neurotrophic factor (GDNF) was first discovered as a potent survival factor for midbrain dopaminergic neurons and was then shown to rescue these neurons in animal models of Parkinson's disease. GDNF is a more potent survival factor for dopaminergic neurons and the noradrenergic neurons of the locus coeruleus than other neurotrophic factors, and an almost 100 times more efficient survival factor for spinal motor neurons than the neurotrophins. The members of the GDNF family, GDNF, neurturin (NTN), persephin (PSP), and artemin (ART), have seven conserved cysteine residues with similar spacing, making them distant members of the transforming growth factor-beta (TGF-beta) superfamily. Like the members of the neurotrophin family, the GDNF-like growth factors belong structurally to the cysteine knot proteins. Like neurotrophins, GDNF family proteins are responsible for the development and maintenance of various sets of sensory and sympathetic neurons but, in addition, GDNF and NTN are also responsible for the development and survival of the enteric neurons, and NTN for parasympathetic neurons. All neurotrophins bind to the p75 low-affinity receptor, but their ligand specificity is determined by trk receptor tyrosine kinases. GDNF, NTN, PSP, and ART mediate their signals via a common receptor tyrosine kinase, Ret, but their ligand specificity is determined by a novel class of glycosylphosphatidylinositol (GPI)-anchored proteins called the GDNF family receptor alpha (GFR alpha). GDNF binds preferentially to GFR alpha1, NTN GFR alpha2, ART GRF alpha3, and PSP GFR alpha4 as a co-receptor to activate Ret. GFR alpha4 has until now been described only from chicken. Although the GDNF family members signal mainly via Ret receptor tyrosine kinase, there is recent evidence that they can also mediate their signals via GFR alpha receptors independently of Ret. The GDNF family of growth factors, unlike neurotrophins, has a well-defined function outside the nervous system. Recent transgenic and organ culture experiments have clearly demonstrated that GDNF is a mesenchyme-derived signaling molecule for the promotion of ureteric branching in kidney development. NTN, ART, and PSP are also expressed in the developing kidney, and NTN and PSP induce ureteric branching in vitro, but their true in vivo role in kidney morphogenesis is still unclear.

Mutation and deletion analysis of GFR alpha-1, encoding the co-receptor for the GDNF/RET complex, in human brain tumours

Glial cell line-derived neurotrophic factor (GDNF) plays a key role in the control of vertebrate neuron survival and differentiation in both the central and peripheral nervous systems. GDNF preferentially binds to GFRalpha-1 which then interacts with the receptor tyrosine kinase RET. We investigated a panel of 36 independent cases of mainly advanced sporadic brain tumours for the presence of mutations in GDNF and GFRalpha-1. No mutations were found in the coding region of GDNF. We identified six previously described GFRalpha-1 polymorphisms, two of which lead to an amino acid change. In 15 of 36 brain tumours, all polymorphic variants appeared to be homozygous. Of these 15 tumours, one also had a rare, apparently homozygous, sequence variant at codon 361. Because of the rarity of the combination of homozygous sequence variants, analysis for hemizygous deletion was pursued in the 15 samples and loss of heterozygosity was found in 11 tumours. Our data suggest that intragenic point mutations of GDNF or GFRalpha-1 are not a common aetiologic event in brain tumours. However, either deletion of GFRalpha-1 and/or nearby genes may contribute to the pathogenesis of these tumours.

Neuroprotective utility and neurotrophic action of neurturin in postnatal motor neurons: comparison with GDNF and persephin

Neurturin and persephin are recently discovered homologs of glial cell line-derived neurotrophic factor (GDNF). Here, we report that neurturin, like GDNF, increases the choline acetyltransferase activity of normal postnatal motor neurons, induces neurite outgrowth in spinal cord, and potently protects motor neurons from chronic glutamate-mediated degeneration. Persephin, in contrast, does not appear to have neurotrophic or neurite-promoting effects on mature motor neurons and may instead worsen the glutamate injury of motor neurons. This pattern in the TGF-beta family suggests certain receptor specificities, requiring at least the Ret/GFRalpha-1 receptor complex. The results predict potential benefit of neurturin, but not persephin, in the treatment of motor neuron disorders and spinal cord diseases.

GDNF family ligands and receptors are differentially regulated after brain insults in the rat

Expression of mRNAs for glial cell line-derived neurotrophic factor (GDNF), neurturin (NTN) and their receptors was studied in adult rat brain using in situ hybridization after 40 kindling-evoked, rapidly recurring seizures or 10 min of global forebrain ischaemia. Following seizures, GDNF and NTN mRNAs were elevated in dentate granule cells, and c-Ret mRNA in hilar neurons and non-pyramidal cells in CA1 and CA3 regions. GFRalpha-1 mRNA levels showed more widespread increases in the dentate granule cell layer and hilus, CA1 and CA3 pyramidal layers, basolateral amygdala and parietal cortex. The expression of GFRalpha-2 mRNA increased in the piriform cortex and decreased in the CA1 region and basolateral amygdala. Forebrain ischaemia induced elevated expression of GDNF mRNA in dentate granule cells, GFRalpha-1 mRNA in the dentate granule cell layer, hilus and CA3 pyramidal layer, and GFRalpha-2 mRNA in the parietal cortex. The gene expression patterns observed here suggest that GDNF and NTN may act as target-derived factors, but also in an autocrine or paracrine manner. GFRalpha-1 can be coexpressed with GFRalpha-2 and c-Ret mRNAs in the same hippocampal or thalamic neurons, but other neurons contain GFRalpha-1 alone or together with c-Ret mRNA. The gene expression changes for the ligands, and the receptor components are region-, cell- and insult-specific, and occur independently of each other, mainly within 24 h after seizures or ischaemia. This dynamic regulation of GDNF and NTN circuits primarily at the receptor level may be important for the effectiveness of neuroprotective responses but could also trigger plastic changes, e.g. those underlying the development of epileptic syndromes.

Gene targeting reveals a critical role for neurturin in the development and maintenance of enteric, sensory, and parasympathetic neurons

Neurturin (NTN) is a neuronal survival factor that activates the Ret tyrosine kinase in the presence of a GPI-linked coreceptor (either GFR alpha1 or GFR alpha2). Neurturin-deficient (NTN-/-) mice generated by homologous recombination are viable and fertile but have defects in the enteric nervous system, including reduced myenteric plexus innervation density and reduced gastrointestinal motility. Parasympathetic innervation of the lacrimal and submandibular salivary gland is dramatically reduced in NTN-/- mice, indicating that Neurturin is a neurotrophic factor for parasympathetic neurons. GFR alpha2-expressing cells in the trigeminal and dorsal root ganglia are also depleted in NTN-/- mice. The loss of GFR alpha2-expressing neurons, in conjunction with earlier studies, provides strong support for GFR alpha2/Ret receptor complexes as the critical mediators of NTN function in vivo.

GDNF: a novel factor with therapeutic potential for neurodegenerative disorders

The identification of novel factors that promote neuronal survival could have profound effects on developing new therapeutics for neurodegenerative disorders. Glial cell line-derived neurotrophic factor (GDNF) is a novel protein purified and cloned based on its marked ability to promote dopaminergic neuronal function. GDNF, now known to be the first identified member of a family of factors, signals through the previously known receptor tyrosine kinase, Ret. Unlike most ligands for receptor tyrosine kinases, GDNF does not bind and activate Ret directly, but requires the presence of GPI-linked coreceptors. There are several coreceptors with differing affinities for the GDNF family members. The profile of coreceptors in a cell may determine which factor preferentially activates Ret. In vivo differences in localization of the GDNF family members, its coreceptors and Ret suggest this ligand/receptor interaction has extensive and multiple functions in the CNS as well as in peripheral tissues. GDNF promotes survival of several neuronal populations both in vitro and in vivo. Dopaminergic neuronal survival and function are preserved by GDNF in vivo when challenged by the toxins MPTP and 6-hydroxydopamine. Furthermore, GDNF improves the symptoms of pharmacologically induced Parkinson's disease in monkeys. Several motor neuron populations isolated in vitro are also rescued by GDNF. In vivo, GDNF protects these neurons from programmed cell death associated with development and death induced by neuronal transection. These experiments suggest that GDNF may provide significant therapeutic opportunities in several neurodegenerative disorders.

Retarded growth and deficits in the enteric and parasympathetic nervous system in mice lacking GFR alpha2, a functional neurturin receptor

Glial cell line-derived neurotrophic factor (GDNF) and a related protein, neurturin (NTN), require a GPI-linked coreceptor, either GFR alpha1 or GFR alpha2, for signaling via the transmembrane Ret tyrosine kinase. We show that mice lacking functional GFR alpha2 coreceptor (Gfra2-/-) are viable and fertile but have dry eyes and grow poorly after weaning, presumably due to malnutrition. While the sympathetic innervation appeared normal, the parasympathetic cholinergic innervation was almost absent in the lacrimal and salivary glands and severely reduced in the small bowel. Neurite outgrowth and trophic effects of NTN at low concentrations were lacking in Gfra2-/- trigeminal neurons in vitro, whereas responses to GDNF were similar between the genotypes. Thus, GFR alpha2 is a physiological NTN receptor, essential for the development of specific postganglionic parasympathetic neurons.

RET proto-oncogene in the development of human cancer

The RET proto-oncogene, located on chromosome subband 10q11.2, encodes a receptor tyrosine kinase expressed in tissues and tumors derived from neural crest. Germline (present in every cell of the body) mutations in RET cause multiple endocrine neoplasia type 2 (MEN 2), an inherited cancer syndrome characterized by medullary thyroid carcinoma (MTC), pheochromocytoma (PC), and hyperparathyroidism (HPT). This knowledge has allowed molecular diagnosis and presymptomatic DNA-based testing to become possible. RET testing is considered the standard of care in MEN 2 families because clinical decisions are made based on the results of such gene testing. There appears to be a correlation between specific RET mutation type and organ-specific tumor development. Such knowledge might be useful in tailoring targeted surveillance in the near future. Somatic (in the tumor only) RET mutations have been found in a proportion of sporadic MTCs and PCs. Whether the presence of somatic RET mutation is associated with a poor prognosis is currently being investigated as another tool for molecular medicine.

GFR alpha-4 and the tyrosine kinase Ret form a functional receptor complex for persephin

Glial-cell-line-derived neurotrophic factor (GDNF), neurturin and persephin are structurally related, secreted proteins that are widely expressed in the nervous system and other tissues and promote the survival of a variety of neurons during development. GDNF and neurturin signal through multicomponent receptors that consist of the Ret receptor tyrosine kinase and one of two structurally related glycosyl-phosphatidylinositol (GPI)-linked ligand-binding subunits: GFR alpha-1 is the preferred ligand-binding subunit for GDNF, and GFR alpha-2 is the preferred ligand-binding subunit for neurturin. Two additional members of the GFR alpha family of GPI-linked proteins have recently been cloned: GFR alpha-3 and GFR alpha-4. We have shown that persephin binds efficiently only to GFR alpha-4, and labelled persephin is effectively displaced from cells expressing GFR alpha-4 by persephin but not by GDNF or neurturin. Using microinjection to introduce expression plasmids into cultured neurons, we have also shown that coexpression of Ret with GFR alpha-4, confers a marked survival response to persephin but not to GDNF or neurturin. These results demonstrate that GFR alpha-4 is the ligand-binding subunit for persephin and that persephin, like GDNF and neurturin, also requires Ret for signalling.

GFRalpha1 is an essential receptor component for GDNF in the developing nervous system and kidney

Glial cell line-derived neurotrophic factor (GDNF) is a distant member of the TGFbeta protein family that is essential for neuronal survival and renal morphogenesis. We show that mice who are deficient in the glycosyl-phosphatidyl inositol (GPI) -linked protein GFRalpha1 (GDNFRalpha) display deficits in the kidneys, the enteric nervous system, and spinal motor and sensory neurons that are strikingly similar to those of the GDNF- and Ret-deficient mice. GFRalpha1-deficient dopaminergic and nodose sensory ganglia neurons no longer respond to GDNF or to the structurally related protein neurturin (NTN) but can be rescued when exposed to GDNF or neurturin in the presence of soluble GFRalpha1. In contrast, GFRalpha1-deficient submandibular parasympathetic neurons retain normal response to these two factors. Taken together with the available genetic and biochemical data, these findings support the idea that GFRalpha1 and the transmembrane tyrosine kinase Ret are both necessary receptor components for GDNF in the developing kidney and nervous system, and that GDNF and neurturin can mediate some of their activities through a second receptor.