Homozygous <i>mray</i> mutants show severe craniofacial malformations starting early in development.

<p><b>A, B,</b> Fluorescent images of a wild-type embryo compared to a homozygous <i>mray</i> littermate at E12.5. The dashed lines indicate the relative decrease in the size of the forebrain (red) but increase in the size of the midbrain in the mutant (green) respectively. In <b>C</b> and <b>D</b> frontal views of the head photographed under fluorescent lighting illustrate the median cleft of affected mutants. <b>E, F,</b> Nissl-stained coronal sections of the oral cavity of 14.5 day old embryos show that the palatal shelves in homozygous <i>mray</i> mutants fail to sufficiently grow out and eventually fuse. FB: forebrain, MB: midbrain, OC: oral cavity, PS: palatal shelf, TB: tooth bud, To: tongue. Scale bars in <b>A–D</b> are 1 mm and in <b>E</b> and <b>F</b> 250 μm.