Whole-mount in situ hybridization reveals the expression of the Xl-Fli gene in several lineages of migrating cells in Xenopus embryos

The expression of the Xl-Fli gene, which belongs to the ets family of transcription factors, was studied by whole-mount in situ hybridization during Xenopus embryogenesis. Digoxigenin-labeled antisense RNA probes were synthesized by in vitro transcription and used in the hybridization reaction. In addition to expression in territories invaded by neural crest cells reported earlier (Meyer et al., 1993), we observed Xl-Fli gene expression in a number of regions affected by important cellular migrations and/or epitheliummesenchyme transitions: in the endothelial cells of the heart, in blood vessels, along the pronephric duct migration pathway and at the level of hypophysis. The possibility that the FLI protein is involved in the expression of guidance cues and/or modification of the cellular adhesion properties is discussed. A screening of a promoter library with a consensus sequence, bound by the FLI protein with a high affinity, revealed the presence of putative FLI response elements in a number of genes encoding adhesion molecules or components of the extra-cellular matrix.