Intercellular Wnt signalling is required for many patterning processes in vertebrate development. Kelly and colleagues now report that the Wnt co-receptors Lrp5 and Lrp6 - members of the LDL receptor-related family -transduce the Wnt signals that drive posterior patterning during mouse gastrulation (see p. 2803). The researchers show that Lrp5/6double-mutant embryos fail to establish a primitive streak at gastrulation but establish anterior patterning correctly, a phenotype also seen in Wnt3 mutant embryos. The phenotypes of embryos carrying various combinations of wild-type and mutated Lrp5 and Lrp6 genes indicate that the co-receptors function redundantly. Finally, the phenotype of Lrp5+/-;Lrp6-/- embryos - mesodermal defects that closely resemble those seen in Fgf8 and Fgfr1 mutant embryos, and altered anterior patterning that correlates with increased Nodal expression - indicates that Wnt, Fgf and Nodal signals interact to pattern the early mouse embryo.

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