XB-ART-851Development February 1, 2006; 133 (3): 485-94.
Ras-dva, a member of novel family of small GTPases, is required for the anterior ectoderm patterning in the Xenopus laevis embryo.
Ras-like small GTPases are involved in the regulation of many processes essential for the specification of the vertebrate body plan. Recently, we identified the gene of novel small GTPase Ras-dva, which is specifically expressed at the anterior margin of the neural plate of the Xenopus laevis embryo. Now, we demonstrate that Ras-dva and its homologs in other species constitute a novel protein family, distinct from the previously known families of small GTPases. We show that the expression of Ras-dva begins during gastrulation throughout the anterior ectoderm and is activated by the homeodomain transcription factor Otx2; however, later on, Ras-dva expression is inhibited in the anterior neural plate by another homeodomain factor Xanf1. Downregulation of Ras-dva functioning by the dominant-negative mutant or by the antisense morpholino oligonucleotides results in severe malformations of the forebrain and derivatives of the cranial placodes. Importantly, although the observed abnormalities can be rescued by co-injection of the Ras-dva mRNA, they cannot be rescued by the mRNA of the closest Ras-dva homolog from another family of small GTPases, Ras. This fact indicates functional specificity of the Ras-dva signaling pathway. At the molecular level, downregulation of Ras-dva inhibits the expression of several regulators of the anterior neural plate and folds patterning, such as Otx2, BF-1 (also known as Foxg1), Xag2, Pax6, Slug and Sox9, and interferes with FGF8 signaling within the anterior ectoderm. By contrast, expression of the epidermal regulator BMP4 and its target genes, Vent1, Vent2b and Msx1, is upregulated. Together, the data obtained indicate that Ras-dva is an essential component of the signaling network that patterns the early anterior neural plate and the adjacent ectoderm in the Xenopus laevis embryos.
PubMed ID: 16410411
Article link: Development
Genes referenced: ag1 bmp4 fgf8 hesx1 msx1 otx2 pax6 ras-dva1 snai2 sox9 ventx1.2
Morpholinos: ras-dva1 MO1
Article Images: [+] show captions
|Fig. 2. Normal expression patterns of Ras-dva and its transcriptional regulators, the homeobox genes Otx2 and Xanf1, in the gastrula and neurula stage Xenopus embryos as revealed by whole-mount in situ hybridization. All embryos are shown from the anterior, dorsal side upwards. Broken line indicates the neural plate border. (A) At midgastrula (stage 11) the Ras-dva is diffusely expressed within a broad territory that includes the presumptive anterior neural and non-neural ectoderm. (B) At late gastrula (stage 12.5) the Ras-dva expression weakens in the area corresponding to the anterior neural plate but it increases in the surrounding area. (C) At the midneurula (stage 14) Ras-dva is expressed in cells of the non-neural anterior ectoderm and in the lateral neural folds. (D-F) Normal expression patterns of the homeobox genes Otx2 and Xanf1. Although Ras-dva and Xanf1 are expressed in mutually excluding domains, the expression domains of Ras-dva and Otx2 are largely overlapping. (G,H) The results of in situ hybridization in halves of Xenopus embryos on the 12.5 and 14 stages. Left halves show the expression of Otx2 gene, right halves show Ras-dva expression. (I) The Xenopus embryo (stage 13) in which the left half is stained for Xanf1 expression and the right half is stained for Ras-dva expression. (J) The scheme of expression patterns of Ras-dva, Otx2 and Xanf1 at the midneurula stage (stage 14).|