The long term goal of the proposed research is to understand the molecular mechanisms by which Wnts convey developmental information in vertebrates. A primary goal of the present study is to examine the mechanisms by which wnt-8 contributes to abnormal or normal patterning by testing the hypotheses (a) that misexpression of Xwnt-8 in anterior mesoderm either retards the normal involution of this tissue or alters its neural inducing activity thereby leading to a loss of forebrain and (b) that misexpression of Xwnt-8 in prospective dorsal mesoderm leads to identifiable changes in gene expression that promote ventral rather than dorsal differentiation. A number of related Xenopus Wnts have been identified whose developmental functions remain unexplored. One such gene, Xwnt-8b, which is more closely related to Xwnt-8 than it is to other Wnts, is transiently expressed during the same developmental stages as Xwnt-8 but in different cell types. To initiate functional analysis of Xwnt-8b and to examine structure/function relationships to both Xwnt-8b and Xwnt-8, Dr. Christian will test the hypotheses: (a) that maintenance of the usual expression pattern of Xwnt-8b is required for normal embryonic patterning and (b) that specific, identifiable domains of Xwnt-8 and Xwnt-8b mediate their distinct biological activities and biochemical characteristics. Specific aims are: (1) analysis of mechanisms underlying the Xwnt-8 mediated loss of forebrain; (2) identification and cloning of zygotic genes involved in dorsal or ventral specification; (3) cloning of the complete coding region of the Xwnt-8b cDNA; (4) analysis of embryonic expression of Xwnt-8b transcripts; (5) perturbation of normal expression of Xwnt-8b; and (6) identification of functional domains of Xwnt-8b.