EXPRESSION OF A NEW G-PROTEIN-COUPLED RECEPTOR X-MSR IS ASSOCIATED WITH AN ENDOTHELIAL LINEAGE IN XENOPUS-LAEVIS

In order to determine whether G protein-coupled receptors play a role in early embryogenesis, we looked for cDNA fragments amplified between primers located in consensus sequences of transmembrane segments. Usi ng one such amplified fragment as a probe, we cloned a novel member of the G protein-coupled receptor superfamily in Xenopus. Alignment of t he deduced protein sequence with that of other receptors discloses som e homology with angiotensin receptors. A single transcript of 2.5 kb i s detected at the late blastula stage and its expression increases dur ing gastrulation. In situ hybridization reveals transcripts initially in the ventrolateral involuting marginal zone and later in the lateral plate mesoderm. At larval stages, the transcript is expressed in proc ardiac tube and forming blood vessels, where it is localized in the in ner endothelial layer. Thus, this gene traces an endothelial lineage a nd represents a very early and unique marker in Xenopus of the specifi cation of cardiac and vascular endothelia. We propose the name of X-ms r for mesenchyme-associated serpentine receptor.