GDNF expression during Xenopus development.

Glial cell line-derived neurotrophic factor (GDNF) has multiple roles in kidney morphogenesis, spermatogenesis, and neurogenesis during development. In this study, we report the cloning and expression pattern of Xenopus laevis GDNF. The X. laevis GDNF cDNA sequence has a complete open reading frame of 684 bases, predicting 227 amino acid residues at the protein level. Comparison of the X. laevis GDNF amino acid sequence with those of chick, human, mouse, rat and zebrafish indicates that X. laevis GDNF has 60%-52% and 75%-62% identity over the whole amino acid sequence and for the putative mature forms, respectively. All known functional motifs of GDNF were conserved in the X. laevis sequence. Temporal expression analysis by RT-PCR indicated that GDNF transcripts were first detectable at stage 12 at a low level, and gradually increased up to stage 22. From stage 24, the expression sharply increased and continued at a similar level as development progressed. Spatial expression analysis by whole-mount in situ hybridization showed that the GDNF mRNA was predominantly detected in somites, pronephros, pharyngeal arches, epibranchial placodes, digestive tract and some of the lateral line structure. These results suggest that this X. laevis gene is the orthologue for GDNF.