A pattern of precision

The amazing precision with which different cell types find their correct locations in developing tissues has fascinated biologists for decades. Models of cell fate patterning during development emphasize the contrast between spatial gradients of developmental signals that act at long range and cell-to-cell signaling events that act locally. Development of the vulva in the nematode Caenorhabditis elegans provides an elegant model system for examining the patterning of cell fate in an animal. There is strong evidence that two different intercellular signals contribute to the relatively simple induction of cell fate among vulval precursor cells (VPCs): a long-range spatial gradient of epidermal growth factor (EGF) mediated by the EGF receptor (1, 2) and a cell-to-cell lateral signal mediated by the Notch-like receptor LIN-12 (3–5).