Overexpression of a homeodomain protein confers axis-forming activity to uncommitted xenopus embryonic cells

Abstract

The anteroposterior character of mesoderm induced by a peptide growth factor (XTC-MIF) was tested by transplantation into host Xenopus gastrulae. Both retinoic acid and a homeodomain protein were able to override the anteriorizing effect of the growth factor. Microinjection of a posteriorly expressed homeobox mRNA can respecify anteroposterior identity, transforming head mesoderm into tail-inducing mesoderm. Unexpectedly, overexpression of XIHbox 6 protein in the transplanted cells, without addition of growth factors, caused the formation of tail-like structures. The cells overexpressing XIHbox 6 were able to recruit cells from the host into the secondary axis. The results suggest that vertebrate homeodomain proteins are part of the biochemical pathway leading to the generation of the body axis.

Antagonizing the Spemann organizer: role of the homeobox gene Xvent-1.

“…Microinjection of XlHbox-6 interferes with dorsal mesodermal develoment as well as with neural development and leads to severely malformed embryos that exhibit spina bifida (Cho et al, 1991b;Niehrs and De Robertis, 1991). An involvement of XlHbox-6 in early ventral mesodermal development is unlikely, since it is not expressed at gastrula stages but only from early neurula onwards (Sharpe et al, 1987).…”

Regulation of vertebrate homeobox‐containing genes by morphogens

“…Wnt factors cause injected cells to act as a Nieuwkoop centre, the vegetal-inducing component of normal dorsal axis formation, as they induce, but do not contribute to, the secondary dorsal axis [86]. Injection of Wnt-8 induces ectopic expression of the homeobox-containing gene goosecoid, normally expressed only in the dorsal blastopore lip [71], into the whole marginal zone (E. De Robertis, personal communication). Injection of goosecoid mRNA into ventral blastomere also causes induction of a complete secondary axis [71].…”

“…Injection of Wnt-8 induces ectopic expression of the homeobox-containing gene goosecoid, normally expressed only in the dorsal blastopore lip [71], into the whole marginal zone (E. De Robertis, personal communication). Injection of goosecoid mRNA into ventral blastomere also causes induction of a complete secondary axis [71]. This suggests that goosecoid might play a key role in executing the Spemann's organizer function of the dorsal blastopore lip, possibly induced by a Wnt-type growth factor mediating the activity of the Nieuwkoop centre.…”

A novel, activin-inducible, blastopore lip-specific gene of Xenopus laevis contains a fork head DNA-binding domain.

“…As seen in Figure 7, XFKHl gene expression can be induced in animal caps even if the animal caps are preincubated in cyclohexamidc, a potent inhibitor of protein synthesis. This treatment reduces the protein synthesis by 75-95% (Rosa 1989;Cho et al 1991b). The amount of RNA is reduced but not eliminated.…”