XENOPUS XSAL-1, A VERTEBRATE HOMOLOG OF THE REGION-SPECIFIC HOMEOTIC GENE SPALT OF DROSOPHILA

We have isolated an amphibian homolog of the homeotic gene spalt of Dr osophila. Like its Drosophila counterpart the Xenopus Xsal-1 gene enco des a protein that contains three widely separated sets of sequence re lated double zinc finger motifs of the CC/HH-type as well as a single CC/HH zinc finger. The Xenopus gene encodes a fourth double zinc finge r and a single CC/HC zinc finger motif that have no counterpart in the fly protein. Alternative splicing of Xsal-1 transcripts gives rise to RNAs coding for either four, three, or two double zinc fingers, respe ctively. The main expression domains of Xsal-1 in early development ar e confined to distinct regions along the lateral axon tracts within th e midbrain, hindbrain, and spinal cord. Outside the central nervous sy stem Xsal-1 is expressed in the facio-acoustic ganglion and in the dev eloping limb buds. The pattern of expression suggests that Xsal-1 migh t be under control of signals emanating from the notochord and/or the floor plate and that it might function in neuronal cell specification.