Amino acid sequence and embryonic expression of msr/apj, the mouse homolog of Xenopus X-msr and human APJ.

We have recently identified a new G protein-coupled receptor, X-msr, whose expression is associated with the endothelial lineage in Xenopus laevis (Devic, E., Paquereau, L., Vernier, P., Knibiehler, B., Audigier, Y., 1996. Expression of a new G protein-coupled receptor X-msr is associated with an endothelial lineage in Xenopus laevis. Mech. Dev. 59, 129-140). Based on its structural analogy to the human orphan receptor APJ, we cloned the murine msr/apj receptor and analyzed its expression in developing tissues. As observed for X-msr, msr/apj transcripts are detected in the endothelium of the primary blood vessels and the forming heart. In addition, they are expressed in somites, limb bud and branchial arches. This expression pattern is distinct from that of the Flk1 gene and suggests that the msr/apj gene is expressed in a subpopulation of endothelial precursors and a mesenchymal population derived from paraaxial mesoderm.