Developmental expression of the Xenopus laevis Tbx20 orthologue

Abstract

We have isolated the Xenopus orthologue of the T-box gene, Tbx20, and characterized its developmental expression profile. We show that Tbx20 is one of the earliest markers of heart tissue in Xenopus, and is expressed throughout all cardiac tissue during later stages of development. In addition, we also observe expression in the cement gland, the jugular vein, the lung bud, the cloacal aperture, rhombomeres 2, 4, 6 and 8, and in a subset of motor neurons.

Fig. 1

A, B Comparative sequence analysis of TBX20. Analysis was performed with the GeneDoc program. A Alignment of vertebrate TBX20 proteins. Fully conserved amino acids including those containing conservative substitutions are shaded in dark gray. Lighter shading represents lower conservation. The conserved T-box domain is underlined in black. B Vertebrate TBX20 amino acid conservation. The percentage of identical amino acid residues (identity) and the percentage of conservative substitutions and identical residues (similarity) are given for comparison between TBX20 proteins. TBX20 prefixes: x, Xenopus; z, zebrafish; c, chicken; m, mouse; h, human

Fig. 2

Temporal expression of Xenopus laevis Tbx20 as detected by RNase protection assay. Ornithine decarboxylase (ODC) is included in the lower panel as an internal loading control

Fig. 3

A–L Expression of Tbx20 during Xenopus laevis development as detected by whole-mount in situ hybridization. A Anterior view of a stage-13 embryo. Dorsal side is facing up. B Anterior view of a stage-16 embryo. Dorsal side is facing up. C Ventral view of the anterior portion of a stage-27 embryo. D Ventral view of the anterior portion of a stage-32 embryo. E Lateral view of the anterior portion of a stage-35 embryo. F Higher magnification of E. G Dorsolateral view of a stage-35 embryo. H Ventral view of the posterior portion of a stage-27 embryo. I–L Sections of stage-35 embryos. I Anterior view of a parasagittal section. J Transverse section through the anterior region. K, L Higher magnifications of J. ca Cloacal aperture, cg cement gland, e endocardium, ey eye, h heart, hb hindbrain, hp heart primordium, it inflow tract, jv jugular vein, l liver, lb lung bud, m myocardium, mn motor neuron, nch notochord, ot outflow tract, st septum transversum, R2–R8 rhombomeres 2, 4, 6, and 8