Notebook

Reprinted with permission from Nature

CKI produces complete secondary dorsal axes. Synthetic mRNA encoding CKI, mutant CKI (K > R), or Xwnt-8 was injected at the eight-cell stage into one ventral vegetal blastomere. Embryos injected with CKI or Xwnt-8, but not inactive CKI (K > R), developed complete secondary dorsal axes.

CANCER CLUE The rush of discoveries over the past two years concerning the Wnt signaling pathway--known to be crucial to normal development and altered in human melanoma and colon cancers--has uncovered an as-yet unnamed complex of proteins within the cell that appear to function together as a machine. Wnt signals regulate this developmental machinery by binding with membrane receptors to enter the cell and influence gene expression from the nucleus. Now another component in this convoluted signaling cascade has been established and its likely position identified (J.M. Peters et al., "Casein kinase I transduces Wnt signals," Nature, 401...