Figure 7. Model.

end-1 and end-3 are activated in the E blastomere as a result of P₂-to-EMS signaling and function redundantly to regulate all currently quantifiable characteristics of the E lineage. However, there are also genes, like sdz-23, that are expressed specifically in the E lineage and which also require P₂-to-EMS signaling for their activation. Intriguingly, these genes do not appear to be involved in intestine specification or development, and do not appear to be regulated by end-1 or end-3.