External craniofacial features, body size, and renal morphology in prenatal brachyrrhine mice.

The Brachyrrhine (Br) semidominant mouse mutant provides a useful model for studying factors responsible for midfacial hypoplasia. In order to determine early morphogenetic events responsible for midfacial hypoplasia in these mice, prenatal mutants must be differentiated from nonaffected littermates. The purpose of this study was to determine whether prenatal offspring from Br matings could be separated morphologically into groups of normal or midfacially deficient embryos. Thirty embryos resulting from Br matings were collected between day 15 and birth (Theiler stages 23-27). Qualitative observations on craniofacial morphology as well as renal morphology and histology suggested that embryos segregated into two distinct groups. External craniofacial and body measurements, collected from the embryos, as well as renal volumes, determined from computerized reconstructions of the kidneys, were subjected to quantitative analyses. A discriminant function analysis segregated the sample into two groups based primarily on midfacial length and renal volume. Bivariate regression analysis showed that midfacial length and renal volume differed significantly, and cranial length marginally so, between the two groups. The results indicate that a proportion of prenatal offspring from Br matings exhibits midfacial and renal hypoplasia and that these animals segregate completely from nonaffected embryos.