Differential expression of the HMG box transcription factors XTcf-3 and XLef-1 during early Xenopus development

Abstract

The recent discovery that the HMG box transcription factor XTCF-3 is involved in early axis specification in Xenopus laevis (Molenaar, M., van de Wetering, M., Oosterwegel, M., Peterson-Maduro, J. Godsave, S., Korinek, V., Roose, J., Destree, O., Clevers, H., 1996. XTcf-3 transcription factor mediates beta-catenin-induced axis formation in Xenopus embryos. Cell 86, 391-399) led us to search for other members of the TCF/LEF family in this species. A newly identified HMG box factor was cloned with highest homology to human LEF-1, called XLEF-1. Unlike XTcf-3, XLef-1 is not expressed maternally, but its transcripts become detectable directly after the mid blastula transition (MBT). At later stages, both genes are expressed in the central nervous system (CNS), eyes, otic vesicles, head mesenchyme, neural crest and derivatives, branchial arches, developing heart, tailbud and limb buds. The expression pattern of Lef-1 during later stages of development is evolutionarily conserved.

Lef1 plays a role in patterning the mesoderm and ectoderm in Xenopus tropicalis

“…A more extensive phylogenetic analysis is required to determine whether this exon was acquired in mammalian genomes or lost in amphibians and fish. We have shown by northern-blot analysis that lef1 produces only one mRNA during early Xenopus development (Molenaar et al, 1998). In addition, screening of Xenopus cDNA libraries and 5'-RACE did not uncover evidence for alternative splicing of lef1 (data not shown).…”

“…Xenopus lef1 cDNA sequences reported so far (Molenaar et al, 1998) do not contain the exon, annotated as VI in human LEF1, which is also represented in other Tcf/Lef members (Arce et al, 2006). LEF1 exon VI encodes an activation domain and exon VI isoforms may have different functions during development (Gradl et al, 2002).…”

“…The endogenous expression pattern of Lef1 in the mouse and Xenopus indicates additional functions also during early development (Oosterwegel et al, 1993;Molenaar et al, 1998;Galceran et al, 1999). Xenopus lef1 is expressed at high levels in the branchial arches and neural crest derived cells, in the developing heart, lateral plate mesoderm, the tail bud, fins and the mesencephalon (Molenaar et al, 1998).…”

“…Xenopus lef1 is expressed at high levels in the branchial arches and neural crest derived cells, in the developing heart, lateral plate mesoderm, the tail bud, fins and the mesencephalon (Molenaar et al, 1998). In addition, Lef1 and Tcf1 double mutant mice showed additional developmental abnormalities compared to the single mutants and demonstrated redundant functions between Lef1 and Tcf1 during development (Galceran et al, 1999).…”

“…In Xenopus, lef1 expression starts at stage 9 (Molenaar et al, 1998) just prior to mesoderm specification and successive patterning of the mesoderm during gastrulation. Mesoderm patterning is under the control of different signaling pathways including Wnt signaling.…”