Short‐faced mice and developmental interactions between the brain and the face

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Abstract
The length of the face represents an important axis of variation in mammals and especially in primates. Mice with mutations that produce variation along this axis present an opportunity to study the developmental factors that may underlie evolutionary change in facial length. The Crf4 mutant, obtained from the C57BL/6J (wt/wt) background by chemical mutagenesis by the Baylor Mouse Mutagenesis Resource, is reported to have a short-faced phenotype. As an initial step towards developing this model, we performed 3D geometric morphometric comparisons of Crf4 mice to C57BL/6J wild-type mice focusing on three stages of face development and morphology--embryonic (GD 9.5-12), neonatal, and adult. Morphometric analysis of adult Crf4 mutants revealed that in addition to a shortened face, these mice exhibit a significant reduction in brain size and basicranial length. These same features also differ at the neonatal stage. During embryonic face formation, only dimensions related to brain growth were smaller, whereas the Crf4 face actually appeared advanced relative to the wild-type at the same somite stage. These results show that aspects of the Crf4 phenotype are evident as early as embryonic face formation. Based on our anatomical findings we hypothesize that the reduction in facial growth in Crf4 mice is a secondary consequence of reduction in the growth of the brain. If correct, the Crf4 mutant will be a useful model for studying the role of epigenetic interactions between the brain and face in the evolutionary developmental biology of the mammalian craniofacial complex as well as human craniofacial dysmorphology.