Gut Reaction to Wnt Signaling in Worms

its daughter cells differentiate like MS and no longer produce gut (Goldstein 1993). Further nongenetic ma-Department of Molecular, Cellular, and Developmental Biology nipulations of cultured embryonic cells have demonstrated that P 2 is the source of this signal and that the University of Colorado Boulder, Colorado 80309-0347 position of P 2 relative to EMS determines which daughter of EMS produces gut. mom Genes Define a Wnt Pathway That Induces The demonstrations in two papers in this issue of Cell Cell Polarity and Gut Differentiation (Rocheleau et al., 1997; Thorpe et al., 1997) of the The pioneering studies using cultured blastomeres were involvement of a Wnt pathway in very early embryogene-followed by classical genetic screens for mutant em-sis in Caenorhabditis elegans provides another signifi-bryos exhibiting the gutless phenotype expected from cant step toward the ambitious but realistic goal of un-disrupting P 2-EMS signaling (E transformed to MS) (Ro-derstanding all of the basic strategies used to control cheleau et al., 1997; and Thorpe et al., 1997). The two embryogenesis in this model organism. At the same research groups isolated 29 such mutations that define time, they challenge some of the prevailing models of five mom (more mesoderm) genes. Three of the genes Wnt signaling, suggesting that interactions among Wnt have been cloned and found to encode components in pathway components may vary in different develop-the Wnt signal transduction pathway. mom-2 and mental processes. With these papers, as well as the mom-5 encode a Wnt-like molecule and a Frizzled (Fz)-earlier reports on Wnt pathway genes lin-44, lin-17, and like receptor, respectively. mom-1 encodes a protein and new studies on Wnt pathway quired for Wnt protein processing and secretion (Ro-genes reported in recent meetings, worm breeders have cheleau et al., 1997). Using cultured chimeric, partial become a significant force in the army of Wnt research-embryos, Thorpe et al. (1997) determined that mom-1, ers. They have also illustrated how different systems mom-2, and mom-3 (uncloned) act in the signaling P 2 can provide important new complementary insights. cell, and mom-4 (uncloned) acts in the responding EMS Signaling at the Four–Cell Stage Polarizes cell. A function for mom-5 in EMS is assumed based on a Blastomere its Fz-like structure. The establishment of tissue specificity in the early C. Rocheleau et al. (1997) have used RNA-mediated in-elegans embryo is directed by the combination of asym-terference (RNAi) to disrupt the expression of a C. ele-metric cell divisions guided …