Differences in Craniofacial Shape among A/J and C57BL/6J Mice and their F1 Crosses

Abstract

Several studies have found relationships between various craniofacial measurements and the occurrence of cleft lip (CL) in humans as well as mice. Several modes of inheritance have been proposed, some of which involve a maternal effect. In this experiment, dried skulls of CL-susceptible A/J mice, CL-resistant C57BL/6J (C57) mice and Fl mice of the two reciprocal crosses of the same were measured and compared to ascertain whether differences existed between the two Fl strains, depending on the strain of the mother. AB6/F1J (AB6) have the Fl with A/J as the mother and B6A/F1J (B6A) have C57 as the mother. Digital photographs were measured using digitizing software. Groups of two measurements were combined to form ratios describing specific shapes. Measurements and ratios were analyzed using analysis of variance (ANOVA) and discriminant analysis (DA). Oneway ANOV A showed significant differences (p < 0.05) between the two parent strains with both the measurements as well as the ratios, with A/J being smallest and C57 largest in all measurements. Univariate ANOVA controlling for weight showed little difference from the oneway ANOVA. DA was able to correctly classify 100% of both parental strains into their correct strain category.

Measurements between the two Fl strains showed fewer significant differences. The B6A strain was significantly smaller than the AB6 in 3 of the 7 measurements, and the tendency was for it to be smaller in all of the measurements. This placed the Fl strains closer to their paternal strain rather than their maternal strain. The only ratio which showed significant difference between the Fl 's was the premaxillary width to interorbital width in which the B6A exhibited a narrower premaxilla when compared with its interorbital width. This was again more like its paternal strain, though with the remaining 5 ratios, the Fl 's tended to be closer to their maternal strain. DA was able to correctly classify 89% of the Fl 's into their correct strain category, indicating significant differences in overall shape between the Fl 's. Lack of a strong maternal effect in this study may be do to the age of the mice examined and/or small sample size. Future studies may do well to use the euclidean distance matrix analysis to distinguish additional differences between the 4 strains.