XB-ART-18272Development May 1, 1996; 122 (5): 1641-50.
A functional homologue of goosecoid in Drosophila.
We have cloned a Drosophila homologue (D-gsc) of the vertebrate homeobox gene goosecoid (gsc). In the Gsc proteins, the pressure for conservation has been imposed on the homeodomain, the functional domain of the protein: sequence homology is limited to the homeodomain (78% identity) and to a short stretch of 7 aminoacids also found in other homeoproteins such as Engrailed. Despite this weak homology, D-gsc is able to mimic gsc function in a Xenopus assay, as shown by its ability to rescue the axis development of a UV-irradiated embryo. Moreover, our data suggest that the position of insect and vertebrate gsc homologues within a regulatory network has also been conserved: D-gsc expression is controlled by decapentaplegic, orthodenticle, sloppy-paired and tailless whose homologues control gsc expression (for BMP4 and Otx-2), or are expressed at the right time and the right place (for XFKH1/Pintallavis and Tlx) to be interacting with gsc during vertebrate development. However, the pattern of D-gsc expression in ectodermal cells of the nervous system and foregut cannot easily be reconciled with that of vertebrate gsc mesodermal expression, suggesting that its precise developmental function might have diverged. Still, this comparison of domains of expression and functions among Gsc proteins could shed light on a common origin of gut formation and/or on basic cellular processes. The identification of gsc target genes and/or other genes involved in similar developmental processes will allow the definition of the precise phylogenetic relationship among Gsc proteins.
PubMed ID: 8625850
Article link: Development
Species referenced: Xenopus
Genes referenced: bmp4 foxa4 gsc nr2e1 otx2 tbx2 wnt8a
Article Images: [+] show captions
|Fig. 2. Goosecoid proteins in different species. The sequence homology among Gsc proteins is limited to 7 amino acids (GEH for Goosecoid- Engrailed Homology) and the 60 aminoacids of the HD (homeodomain). D-Gsc has a N-terminal extension of 104 residues as compared to its vertebrate counterparts. The cDNA sequence of D-gsc is interrupted by 2 introns (black arrowheads): a 1 kb intron is located at the position of residue 211 and a larger one (8 kb) lies within the HD (at residue 331). The position of the introns of the human, mouse and Xenopus gsc genes is indicated by white arrowheads (Blum et al., 1994) The homeobox of all the gsc genes is interrupted by the second intron, located precisely between amino acid 47 and 48 of the HD. Many examples of genes with an intron lying at this position have been reported, including otx-1, otx- 2, otd, aristaless and evx genes (Duboule, 1994). (* indicates sequence identity).|
|Fig. 3. Functional rescue assay of UV-irradiated Xenopus eggs. After UV-irradiation, Xenopus embryos were microinjected with capped synthetic RNA for lacZ alone (A), bicoid (B), Xwnt-8 (C), X-gsc (D) and D-gsc (E,F). lacZ RNA was included in each sample in order to trace the lineage of the injected cells and revealed using X-gal (blue staining in A-F). The DAI score (DorsoAnterior Index, see Materials and Methods) is indicated for each class of embryos. The red arrows point to the presence of injected cells (lacZ RNA colocalizes with the injected mRNA) in the foregut. The black arrowhead in D and F indicates the restriction of the lacZ-positive cells to the anterior-most region of the tadpole. Anterior is to the left and dorsal to the top.|