EXPRESSION OF A NEW RNA-SPLICE ISOFORM OF WT1 IN DEVELOPING KIDNEY-GONADAL COMPLEXES OF THE TURTLE, TRACHEMYS-SCRIPTA

WT1 is a tumor suppressor gene encoding a zinc finger DNA-binding prot ein required for normal vertebrate kidney and gonad development. Altho ugh the sequence and function of this gene has been studied mostly in mammals, comparative analysis in other vertebrates may suggest regions of conservation of function as well as evolution of function. We have initiated a study of this gene in the freshwater turtle, Trachemys sc ripta, a species that demonstrates temperature dependent sex determina tion. The turtle WT1 amino acid sequence (GenBank Accession No. AF0197 79) is over 85% identical to that of other species overall, but there are some major differences. The greatest differences are in the N-term inal portion of the peptide which is thought to mediate transcriptiona l repression by interaction with other proteins. Turtle WT1, like thos e of the alligator, chicken, and Xenopus lacks the proline- and glycin e-rich stretches that are present in mammalian WT1. Exon 5, which is a lternatively spliced in mammals, is altogether absent in the non-mamma lian vertebrates. In addition, turtle WT1 is alternatively spliced so that exon 4 is either present or absent. These differences suggest tha t the interaction of reptilian WT1 with other factors required for med iation of activity may be different than the interaction of mammalian WT1. It also suggests that alternative splicing is a conserved regulat ory mechanism of vertebrate WT1. Expression of WT1 in turtle embryonic kidney-gonadal complexes begins after the mesonephroi have formed and continues at least until the bipotential gonad begins to differentiat e. Although the proportions of the different splice isoforms are relat ively constant during these stages of kidney development, the level of steady state expression is increased in embryos incubated at 26 degre es C, the testis-producing temperature. (C) 1998 Elsevier Science Inc. All rights reserved.