A role for xGCNF in midbrain-hindbrain patterning in Xenopus laevis.

Cells in the presumptive neural ectoderm of Xenopus are committed to neural fate through a process called neural induction, which may involve proteins that antagonize BMP signaling pathways. To identify genes that are induced by the BMP antagonists and that may be involved in subsequent neural patterning, we used a suppression PCR-based subtraction screen. Here we investigate the prospective activities and functions of one of the genes, a nuclear orphan receptor previously described as xGCNF. In animal cap assays, xGCNF synergizes with ectopic chordin to induce the midbrain-hindbrain marker engrailed-2 (En-2). In Keller explants, which rely on endogenous factors for neural induction, similar increases in En-2 are observed. Expression in embryos of a dominant interfering form of xGCNF reduces the expression of endogenous En-2 and Krox-20. These gain-of-function and prospective loss-of-function experiments, taken with the observation that xGCNF is expressed in the early neural plate and is elevated in the prospective midbrain-hindbrain region, which subsequently expresses En-2, suggest that xGCNF may play a role in regulating En-2 and thus midbrain-hindbrain identity.