Prevalence of interfrontal bones in inbred and F1 mice

Objective: The interfrontal bone (IF) is a minor skeletal trait in mice.  When present the IF bone resides between the frontal bones along the interfrontal (metopic) suture.  IF is considered a quasi-continuous trait and genetic and environmental factors play roles in its development.  The mechanism(s) underlying IF bone development are poorly understood and may involve de novo secondary ossification centers, induction by the interfrontal suture or dura.  We sought to survey inbred strains of mice and selected F1 crosses the prevalence of IF. 

Method: Archived mouse skulls from a Mouse Phenome Project (MPP) and discarded mouse heads from the Collaborative Cross (CC) Project were available for this study.  In total 25 inbred strains and 17 F1 crosses (generated between pairs of CC founder lines) were investigated.  A total of 931 (10-12 wks old) mice representing nearly equal numbers of males and females were phenotyped.  Frozen CC mouse heads were cleaned, bleached, dried, and preserved using polyurethane.  This processing had been performed previously with MPP skulls.  Skulls were viewed dorsally and the IF measured using a zoom stereomicroscope equipped with a calibrated reticle.  Triplicate direct measurements of maximum IF widths and lengths were collected.  Descriptive statistics and comparison of means (ANOVA) were performed. Differences were considered significant when p < 0.05. 

Result: Six of the 25 inbred strains lacked IF.  Prevalence of IF in the remaining strains ranged from 5.0 to 98.3%.  Nine of 17 F1 crosses lacked IF and the prevalence of IF in the remaining F1 crosses ranged from 1.7 to 61.5%.  Comparing males and females among inbred and F1 crosses showed no significant differences between the sexes.

Conclusion: Strain dependent differences in IF will facilitate investigation of genetic and environmental factors contributing to IF development.  (Acknowledge the Mouse Phenome Project and Collaborative Cross Consortium for access to skulls)