Molecular cloning of the Notophthalmus viridescens radical fringe cDNA andcharacterization of its expression during forelimb development and adult forelimb regeneration

Larval and adult newts provide important experimental models to study limb development and regeneration. These animals have exceptional ability to reg enerate their appendages, as well as other vital structures. Our research e xamines the role of the fringe gene (fng) in the developing and regeneratin g adult newt forelimb, Fringe codes for a secretory protein. It was first d iscovered in Drosophila, and later homologues were isolated in Xenopus laev is, chick and mouse. This gene has been highly conserved throughout evoluti on, indicating its crucial role in vertebrate and invertebrate development. We have isolated, cloned, and sequenced the full length of the Notophthalm us viridescens radical fringe cDNA (nrFng) by screening a newt forelimb bla stema cDNA library with a 500-bp fragment of the Xenopus lunatic fringe cDN A, The newt fringe cDNA codes for a 396 amino acid protein with a predicted N-terminal signal sequence. Newt fringe shows high homology with radical f ringe homologues of many species. Whole mount mRNA in situ hybridization on several stages of newt limb development reveals that nrFng is first expres sed in the limb field, with intense expression as the limb bud develops, Ho wever, gene expression diminishes with more advanced digit development. A s ignificant role in adult forelimb regeneration is also evident, as we isola ted the cDNA from a regeneration-specific library and found it highly expre ssed during the regenerative phases of active cell division and then down r egulated at sites undergoing differentiation and morphogenesis. Dev Dyn 199 9;214: 259-268. (C) 1999 Wiley-Liss, Inc.