The genetic control of mammalian embryogenesis is not well understood. N-et
hyl-N-nitrosourea (ENU) mutagenesis screens in the mouse provide a route to
identify more of the genes that are required for mammalian development. Th
e characterization of ENU-induced mutations can build on the resources prov
ided by the mouse and human genome projects to help define the tissue inter
actions and signaling pathways that direct early mammalian development.