Expression pattern of mouse sFRP-1 and mWnt-8 gene during heart morphogenesis

The Wnt genes encode a large family of secreted proteins that play a key ro le in embryonic development and tissue differentiation in many species (Rij sewijk et al., 1987; Nusse and Varmus, 1992). Genetic and biochemical studi es have su,suggested that the frizzled proteins are cell surface receptors for Wnts (Vinson et al 1989; Chan et al., 1992; Bhanot et al., 1996; Wang e t al., 1996). In parallel, a number of secreted frizzled-like proteins with a conserved N-terminal frizzled motif have been identified (Finch et al., 1997; Melkonyan et al., 1997; Rattner et al., 1997). One of these proteins, FrzA, the bovine counterpart of the murine sFRP-1 (93% identity) is involv ed in vascular cell growth control, binds Wg in vitro and antagonizes Xwnt- 8 and bWnt-2 signaling in Xenopus, embryos (Xu et al., 1998; Duplaa et al., 1999). In this study, we report that sFRP-1 is expressed in the heart and in the visceral yolk sac during mouse development, and that sFRP-1 and mWnt -8 display overlapping expression patterns during heart morphogenesis. From 8.5 to 12.5 d.p.c., sFRP-1 is expressed in cardiomyocytes together with mW nt-8 but neither in the pericardium nor in the endocardium; at 17.5 d.p.c., they are no longer present in the heart. In mouse adult tissues, while sFR P-1 is highly detected in the aortic endothelium and media and in cardiomyo cytes, mWnt-8 is not detected in these areas. Immunoprecipitation experimen ts demonstrates that FrzA binds to mWnt-8 in cell culture experiments. (C) 2000 Elsevier Science Ireland Ltd. AU rights reserved.