NORMAL GENOMIC

• Towers PR, Woolf AS, Hardman P
• Glial cell line-derived neurotrophic factor stimulates ureteric bud outgrowth and enhances survival of ureteric bud cells in vitro.
• Exp Nephrol. 1998; 6: 337-51
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• Development of epithelial organs requires co-ordinated interactions between epithelial and mesenchymal tissues. Studies using null mutant mice have indicated that the ret receptor and its ligand, glial cell line-derived neurotrophic factor (GDNF), are crucial for initiation of development of the metanephric kidney. However, the role of this signalling system in other branching organs has not been analysed. Here we describe expression studies of ret, GDNF, and a co-receptor for GDNF (GDNFR alpha) in the developing mouse metanephros, lung, and submandibular salivary gland. Also, we examined the role of this signalling system in the development of these organs in vitro. In situ hybridisation revealed differences in the spatial distribution of the three transcripts in the different organs. At the initiation of metanephric development, late on embryonic day 10 (E10), ret and GDNFR alpha were detected in the Wolffian duct (including the presumptive ureteric bud) whilst the presumptive metanephric, mesenchyme expressed GDNFR alpha and GDNF. Later in development, all three transcripts were restricted to the nephrogenic zone. In contrast, expression in the lung was not detectable by in situ hybridisation until after initiation of development, at E13.5. At this time ret was expressed throughout the epithelium; GDNF was detected throughout the mesenchyme, and GDNFR alpha was present in the proximal epithelium and mesenchyme only. Ret and GDNF were not detected in the epithelium or mesenchyme of the developing salivary gland, however, GDNFR alpha was expressed in the mesenchyme at E13.5 and E16.5. Functional studies demonstrated that in organ culture, GDNF significantly increased branching morphogenesis of the E11.5 metanephros, and induced the formation of ectopic ureteric buds from the base of the bud and from the Wolffian duct. The development of lung and salivary primordia were not affected under similar growth conditions. In a novel ureteric bud primary culture system, GDNF significantly increased cell numbers at 24 and 48 h. In cells cultured on laminin this increase was due to increased survival and proliferation, whereas in cells cultured on fibronectin, only survival was enhanced. Our data suggest that GDNF stimulates outgrowth of the ureteric bud, in part, by enhancing cell survival and possibly by increasing proliferation.

• Shefelbine SE et al.
• Mutational analysis of the GDNF/RET-GDNFR alpha signaling complex in a kindred with vesicoureteral reflux.
• Hum Genet. 1998; 102: 474-8
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• Glial cell line-derived neurotrophic factor (GDNF) mediates signaling across the cell membrane by interaction with the RET-GDNFR alpha receptor complex. We identified a family in which one member had medullary thyroid carcinoma (MTC) and four members had vesicoureteral reflux (VUR). Knowledge that mutations in the RET proto-oncogene cause MTC and studies documenting genitourinary abnormalities in RET or GDNF knockout mice led us to examine the GDNF/RET-GDNFR alpha signaling complex in this family. RET and GDNF were excluded as the causative VUR gene by haplotype and sequence analysis. The GDNFR alpha gene was mapped to chromosome 10q25-26 by radiation hybrid techniques and was eliminated as the causative gene by haplotype analysis and sequencing of cDNA from an obligate carrier. Sequencing identified a 15-nucleotide deletion in GDNFR alpha mRNA, which was found to code for a single exon; analysis of several cell types revealed an identical mRNA form, indicating that this variant is a product of alternative RNA processing. We conclude that GDNFR alpha maps to 10q25-26 and that its RNA transcript is alternatively processed. Mutation abnormalities in the GDNF/RET-GDNFR alpha signaling system do not cause VUR in this family.