Congenital muscle dystrophy and diet consistency affect mouse skull shape differently

Abstract

The bones of the mammalian skull respond plastically to changes in masticatory function. However, the extent to which muscle function affects the growth and development of the skull, whose regions have different maturity patterns, remains unclear. Using muscle dissection and 3D landmark-based geometric morphometrics we investigated the effect of changes in muscle function established either before or after weaning, on skull shape and muscle mass in adult mice. We compared temporalis and masseter mass and skull shape in mice with a congenital muscle dystrophy (mdx) and wild type (wt) mice fed on either a hard or a soft diet. We found that dystrophy and diet have distinct effects on the morphology of the skull and the masticatory muscles. Mdx mice show a flattened neurocranium with a more dorsally displaced foramen magnum and an anteriorly placed mandibular condyle compared with wt mice. Compared with hard diet mice, soft diet mice had lower masseter mass and a face with more gracile features as well as labially inclined incisors, suggesting reduced bite strength. Thus, while the early-maturing neurocranium and the posterior portion of the mandible are affected by the congenital dystrophy, the late-maturing face including the anterior part of the mandible responds to dietary differences irrespective of the mdx mutation. Our study confirms a hierarchical, tripartite organisation of the skull (comprising neurocranium, face and mandible) with a modular division based on development and function. Moreover, we provide further experimental evidence that masticatory loading is one of the main environmental stimuli that generate craniofacial variation.

Masseter muscle atrophy impairs bone quality of the mandibular condyle but not the alveolar process early after induction

“…During development, the mouse mandible changes its shape and size as a result of the eruption of the teeth and the increase of the biomechanical input from masticatory muscles after weaning . These changes affect differently the alveolar process and the mandibular condyle during the transition from juvenile to adult . The maturation of bone in the alveolar process is reached before the ramus, including the mandibular condyle .…”

“…All procedures were approved by the Institutional Animal Care and Use Committee of Universidad de Chile (Certificate Nº 17011‐OD‐UCH). Sample size was based on microCT and bone histomorphometry data from previous studies . Results are reported according to the ARRIVE guidelines.…”

“…5 Also, a change in the dietary regimen from hard to soft food in young adult mice results in a decrease in masseter mass 6 and alters the shape and size of the mandibular condyle [6][7][8] and the alveolar process. 6,7 Moreover, decreased loading using soft diet showed a detrimental effect on subchondral bone in the mandibular condyle of adult mice of both sexes, but the impairment on cell maturation in the condylar cartilage was exclusively found on female individuals. 9 An alternative approach to reduce masticatory load is the intramuscular injection of botulinum toxin type A (BoNTA).…”

“…In turn, altered masticatory loading after masseter muscle resection in young rats leads to asymmetrical growth and reduced bone quality of the mandibular condyle . Also, a change in the dietary regimen from hard to soft food in young adult mice results in a decrease in masseter mass and alters the shape and size of the mandibular condyle and the alveolar process . Moreover, decreased loading using soft diet showed a detrimental effect on subchondral bone in the mandibular condyle of adult mice of both sexes, but the impairment on cell maturation in the condylar cartilage was exclusively found on female individuals …”

La Transición a la Agricultura y la Industrialización Cambiaron la Cara del Ser Humano. ¿Puede el Vegetarianismo ser un Nuevo Factor de Cambio?. Revisión de la Literatura

“…Experimentos en roedores han mostrado que la privación de actividad muscular altera la forma mandibular, particularmente de los procesos condilar, coronoides y angular, además de la forma del crá-neo (Rot-Nikcevic et al, 2007). La reducción de la consistencia de la dieta también es un factor que altera la forma craneofacial en modelo murino, con gracilización craneomandibular (Spassov et al, 2017) y el acortamiento del arco maxilar (Beecher et al, 1981).…”