Fig. 1. Cell interactions that diversify AB descendants. (A) Four-cell and 12-cell embryos showing cells described in the text. ABa, ABp and their descendants each express GLP-1/Notch (green); ABp granddaughters at the 12-cell stage are outlined in bold. (B). Lineage diagram showing the first few divisions of ABa and ABp. Cell fates are shown in the absence of Notch signaling (– Notch) and when both the first (four cell) and second (12 cell) Notch interactions occur (+ Notch). The fates of the ABp descendants called ABpla and ABplp are further modified by the third and fourth Notch interactions, respectively (see Table 1). Signaling from MS leads to PHA-4 expression by the descendants of ABalp and ABara, and in addition represses LAG-2 in ABara descendants.