Comparison and Analysis of Degree of Newborn Neurocranial Bone Development in Two Prdm16 Mutant Mouse Models

This study is part of a larger project examining the role of Prdm16 , a transcriptional cofactor involved in TGF‐β signaling pathways, on craniofacial development. Prdm16 is expressed in various tissues, including cranial neural crest and the brain. Two, Prdm16 mutant mouse models, cleft secondary palate‐1 on a C57Bl6/J background strain ( csp1 ) and Prdm16 conditional gene trap on an FVB/NJ background strain ( cGT ), display non‐syndromic clefting of the secondary palate and micrognathia due to loss of Prdm16 function. Our earlier pilot project on adult cGT and csp1 mice revealed that cGT heterozygous mutants have a relatively narrower skulls compared to their wild type (wt) littermates and that csp1 heterozygous mutants have relatively wider skulls than their wt counterparts. Homozygous mutants of both strains die shortly after birth. The aim of this study is to quantitatively assess variation in bony neurocranial development in newborn het and mut csp1 and cGT mice and contrast this with the wt morphology to determine if variation in degree of bone development in these strains is apparent at the newborn stage. Crania of newborn heterozygous mutant, homozygous mutant, and wt csp1 and cGT mice were microCT scanned and the resulting 2D images were volume‐merged to create a 3D model for each specimen. The neurocranial bones from each 3D model were segmented into separate images for analysis. For each specimen, we calculated the surface area and volume of each neurocranial bone and statistically compared these values among the genotype groupings. Smaller bone surface areas and volumes were interpreted as indicating less bone development. Homozygous mutant mice of both strains had significantly less developed neurocranial bones than their wt counterparts. The heterozygous mutant mice in both strains displayed substantial variation in degree of bone development. The calvarial bones were especially under‐developed in homozygous mutant csp1 and cGT mice, but the occipital and alisphenoid bones were well‐developed in most specimens. Our results suggest that reduced Prdm16 expression in newborn homozygous mutant csp1 and cGT mice correlates with overall underdevelopment of the neurocranium compared to wt mice. Bone development patterns in the heterozygous mutant mice are less apparent and require additional analysis. These findings complement our previous research on adult csp1 and cGT mice and additional insight on the downstream effects of Prdm16 expression on craniofacial development. Support or Funding Information NIH/NIDCR (R15DE023982) and Midwestern University Core Facility