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Assignments of the human dickkopf (Xenopus) homolog 4 (DKK4) to chromosome 8p 11.2->p1.1 by fluorescence in situ hybridization
Rationale and significance
In vertebrates, early embryonic development undergoes the orchestration of the concerted actions of a number of secreted signaling molecules and the dorsal-ventral patterning is partly regulated by a gradient of bone morphogenetic protein (BMP) activity. The gradient is generated by the localized secretion of BMP antagonists such as Chordin and Noggin, which are expressed in the dorsal lip during gastrulation and direct neighboring cells towards the head-axis formation by blocking BMP signaling (Harland and Gerhart, 1997; Krupnik et al., 1999; Oelgeschlager et al., 2000). The Xenopus head-inducing factor Dickkopf- I (xDkk- 1), also expressed in the Spemann's organizer, is a secreted protein that inhibits Wnt signaling pathway and cooperates simultaneously with antagonists of BMP activities (Glinka et al., 1998). A family of four human Dkk-related proteins have been reported and it has been shown that there is a functional heterogeneity among them. Both hDkk- I and hDkk4 suppress the ability of Xwnt8-induced secondary axis formation in Xenopus embryo, whereas, hDkk-2 and hDkk-3 do not. When mRNAs of downstream components of the Wnt signaling pathway such as Xenopus Dishevelled (Xdsh) and Frizzled8 (Xfz8) were expressed ectopically, hDkk-1 and...