Wnt signaling is a key mediator of Cdx1 expression in vivo

Genetics of Wnt signaling during early mammalian development

Proper cell-cell communication is necessary to orchestrate the cell fate determination, proliferation, movement, and differentiation that occurs during the development of a complex, multicellular organism. Members of the Wnt family of secreted signaling molecules regulate these processes in virtually every embryonic tissue and during the homeostatic maintenance of adult tissues. Mammalian genetic studies have been particularly useful in illustrating the specific roles that Wnt signaling pathways play in embryonic development, and in the etiology of diseases such as cancer. This chapter will largely focus on the functional roles that Wnts, signaling through the Wnt/-catenin pathway, play during early mammalian development.

Hox, Wnt, and the evolution of the primary body axis: insights from the early-divergent phyla

The subkingdom Bilateria encompasses the overwhelming majority of animals, including all but four early-branching phyla: Porifera, Ctenophora, Placozoa, and Cnidaria. On average, these early-branching phyla have fewer cell types, tissues, and organs, and are considered to be significantly less specialized along their primary body axis. As such, they present an attractive outgroup from which to investigate how evolutionary changes in the genetic toolkit may have contributed to the emergence of the complex animal body plans of the Bilateria. This review offers an up-to-date glimpse of genome-scale comparisons between bilaterians and these early-diverging taxa. Specifically, we examine these data in the context of how they may explain the evolutionary development of primary body axes and axial symmetry across the Metazoa. Next, we re-evaluate the validity and evolutionary genomic relevance of the zootype hypothesis, which defines an animal by a specific spatial pattern of gene expression. Finally, we extend the hypothesis that Wnt genes may be the earliest primary body axis patterning mechanism by suggesting that Hox genes were co-opted into this patterning network prior to the last common ancestor of cnidarians and bilaterians.