Artefactual gene induction during preparation of Xenopus laevis animal capexplants

The animal cap assay in Xenopus laevis was used to study the induction and regulation of the mesoderm-specific gene Xegr-1, a homolog of the mammalian egr-1 genes, Egr-1 is an immediate-early gene whose growth factor-stimulat ed transcriptional induction displays a transient activity profile and occu rs independent of protein synthesis. The Xegr-1 promoter contains multiple serum response elements (SREs), In this paper we show that Xegr-1 is induce d unspecifically during the process of animal cap preparation. Transcripts of Xegr-1 appear already 30 min after cutting of animal caps. Xfos, another SRE-regulated immediate-early gene, is induced with the sa me kinetics as Xegr-1. In contrast, the Xbra gene is not induced under the experimental co nditions used. Xfos and Xegr-1 transcripts are not rapidly down-regulated a fter mechanical stimulation, but can be detected for up to 4 h rater. Wound ing-dependent Xegr-l induction is reduced by injection of either mRNA codin g for the dominant inhibitory forms of both the FGF receptor and the transc ription factor Elk-l. Xegr-l expression can be reinduced by mesoderm-induci ng factors. These results led us to develop a new protocol for animal cap p reparation, which circumvents the observed undesired artefactual gene activ ation events.