Cre-mediated gene inactivation demonstrates that FGF8 is required for cell survival and patterning of the first branchial arch.

In mammals, the first branchial arch (BA1) develops into a number of craniofacial skeletal elements including the jaws and teeth. Outgrowth and patterning of BA1 during early embryogenesis is thought to be controlled by signals from its covering ectoderm. Here we used Cre/loxP technology to inactivate the mouse Fgf8 gene in this ectoderm and have obtained genetic evidence that FGF8 has a dual function in BA1: it promotes mesenchymal cell survival and induces a developmental program required for BA1 morphogenesis.

The chicken limb deformity gene encodes nuclear proteins expressed in specific cell types during morphogenesis.

The chicken limb deformity (ld) mutation affects morphogenesis of both limbs and kidneys and is one of few murine mutations for which the affected gene has been isolated. Analysis of the chicken homolog reveals evolutionary conservation of large parts of the encoded ld gene products. This is the first study of these proteins, their intracellular localization, and their temporal and spatial distribution during embryogenesis.