The characterization of novel fibroblast growth factor response genes in Xenopus laevis

Abstract

In a search for fibroblast growth factor (FGF)-regulated early response genes, four cDNA fragments were isolated via a polymerase chain reaction-based differential display procedure. The cDNA fragments represent portions of genes that were either activated or repressed in Stage 8 Xenopus laevis explants after a 30 minute treatment with lOOng/ml XFGF-2. One 498bp cDNA fragment, named Band V, represents a gene that is downregulated by FGF treatment. This gene is expressed at Stages 8, 9 and 15 in the developing Xenopus embryo. A Genbank homology search program revealed similarity of Band V to distinct regions in an alternatively spliced myocyte enhancer factor, the v-j- c region of a T-cell receptor gamma chain, a Meprin A beta-subunit precursor and a myosin I heavy chain-like protein. The three other cDNA bands isolated from the differential display were chosen due to apparent upregulation by FGF. The 449bp Band VIA/B cDNA fragment possesses regions of similarity to the reactive centre of murine serine proteinase inhibitor 2.4 and a contrapsin-related MC-7 precursor. Upregulation of Band VIA/B was not confirmed because gene expression could not be detected via PCR in Xenopus explants or throughout development. The third Band 11/12, is a 636bp cDNA fragment whose gene is only expressed at Stage 8 of the developing embryo and was upregulated by FGF-2, in a PCR reaction. A database homology search showed that Band 11/12 was similar to a hypothetical protein. A second, 190bp DNA fragment isolated from Band 12 was a portion of the c-mos protooncogene. The fourth and final cDNA Band 22 is 517bp in size and represents a previously cloned Xenopus 146kDa nuclear splicing factor (Schmidt-Zachmann et aL, 1998). This factor is expressed throughout Xenopus development, and control of Band 22 gene expression by FGF-2 could not be confirmed.