March 1, 2001;
Xath2, a bHLH gene expressed during a late transition stage of neurogenesis in the forebrain of Xenopus embryos.
We have identified a Xenopus bHLH gene, Xath2
, which is the homologue of the murine MATH-2/NEX-1 gene, using a functional expression screening approach. Overexpression of this gene in neurula
embryos induces the expression of the N-tubulin neuronal marker but does not stimulate the expression of the X-ngnr
-1 and NeuroD
proneural genes. Expression of Xath2
begins in stage 32 embryos and is restricted to the dorsal telencephalon
. Within the neuroepithelium of the dorsal telencephalon
expression is detected in postmitotic cells located more laterally than those expressing several other related bHLH neuronal regulators.
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Fig. 1. Induction of N-tubulin, but not X-ngnr-1 and NeuroD expression, by injection of Xath2 mRNA. Xenopus embryos were coinjected with Xath2 and β-galactosidase mRNA (0.5 ng/blastomere) on one side at the two-cell stage. Neural plate stage injected embryos were then stained with X-gal to detect β-galactosidase, followed by whole-mount in situ hybridization with a N-tubulin (A), NeuroD (B) or X-ngnr-1 probe (C).
Fig. 3. Expression of Xath2 during Xenopus development. (Top panels) RNAase protection analysis of Xath2 transcripts during embryogenesis and in adult organs. The FGF receptor is used as an internal control. (Bottom panels) Whole-mount in situ hybridization using Xath2 antisense RNA on stage 35 embryos. (A) Lateral view; (B) dorsal view; (C) parasagittal section; (D) transverse section; (E) horizontal section; (F) double labeling for BrdU incorporation (green) and Xath2 expression (black) on a horizontal section. E, egg.
Fig. 4. Expression of Xath2 compared with other genes expressed in the dorsal forebrain. (Top panels) Stained double in situ hybridized embryos (st. 35) with Xath2 (black) and Eomesodermin (red) were gelatin-embedded and vibratome-sectioned at 30 μm. (A) Horizontal and (B) parasagittal sections. (Bottom panels) Double in situ hybridization on sections with Xath2 (red) and the bHLH genes Xath3 and NeuroD (black). (C,D) Horizontal sections of st. 35 embryos. (E,F) Transverse sections of dissected brains (st. 54) at the level of the telencephalon.