Postnatal Ontogeny of the Cranial Base and Craniofacial Skeleton in Male C57BL/6J Mice: A Reference Standard for Quantitative Analysis

Abstract

Growth of the craniofacial skeleton is a complex process controlled by both genetic and epigenetic factors, perturbations of which can lead to varying degrees of dysmorphology. Mouse models that recapitulate clinical craniofacial phenotypes are instrumental in studying the morphogenetic progression of diseases as well as uncovering their genetic and molecular bases. Commonly encountered phenotypes in these models include defects in the cranial base synchondroses, calvarial sutures, mandible or the midface, or any combination thereof, with the concurrent presence of altered overall craniofacial growth. However, the literature lacks an adequate normative timeline of developmental events and growth trends that shape the mouse craniofacial skeleton. In this report, we analyzed the postnatal craniofacial ontogeny (from postnatal day 7 [P7] through to P112) of male mice from the most widely used inbred mouse strain, C57BL/6J, using high-resolution microcomputed tomography (μCT) in combination with classic morphometric approaches. We also evaluated cranial base synchondroses at the histological level, and compared it to μCT-generated data to assess the timing and pattern of closure of these structures. Our data underscore the complex and unique growth patterns of individual bones and cranial regions and highlight the need to include younger animals in studies aimed at analyzing craniofacial growth processes. Furthermore, these data serve as a reference standard for future quantitative work.

Sclerostin Antibody–Induced Changes in Bone Mass Are Site Specific in Developing Crania

“…Our study was initially designed to examine the effect of Scl‐Ab over a period of rapid long‐bone growth . However, approximately 80% of overall cranial growth in mice occurs during 7 to 14 days of age . We began treatment of mice at age 21 days, which developmentally corresponds to a human age of approximately 2 years based on overall central nervous system and reproductive development .…”

Thyroxine Exposure Effects on the Cranial Base

“…Both low (~167ng/day) and high dosages of levothyroxine correlate with decreased bone volume in the cranial base at P20. The cranial base has a primary role in driving postnatal growth and form, and both the inter-sphenoidal and spheno-occipital (ISS and SOS) synchondroses remain patent in wild-type mice up to P20 [43]. The decreased bone volume with exposure seen at P20 could indicate a delay in ablation of the cartilaginous regions of the cranial base.…”

“…Fusion of the pre- and basi-sphenoid and basioccipital bones normally occurs via bony outgrowths extending from the ectocranial margins of the bones of the cranial base. Thus, some areas of the synchondrosis remain patent while others fuse [43]. Cranial dysmorphology may arise from abnormal cranial base, facial bone, or calvarial suture growth.…”

“…Cranial dysmorphology may arise from abnormal cranial base, facial bone, or calvarial suture growth. Small but biologically significant changes in any of these regions, may be difficult to observe radiographically, but can result in craniofacial abnormalities [18, 43, 44]. Further, changes in the growth trajectory of the cranial base may contribute to craniofacial growth disturbances [21–23].…”

“…The most dramatic effects of levothyroxine exposure on the morphology of the cranial base are observed at P20 indicating that levothyroxine exposure may interfere with expected synchondrosis fusion [43]. That the low dose exposure was observed to have a greater overall effect on synchondroses morphology may be indicative of a response that is specific to that dosage.…”