Plasticity of mandibular biomineralization in myostatin‐deficient mice

Abstract

Compared with the normal or wild-type condition, knockout mice lacking myostatin (Mstn), a negative regulator of skeletal muscle growth, develop significant increases in relative masticatory muscle mass as well as the ability to generate higher maximal muscle forces. Wild-type and myostatin-deficient mice were compared to assess the postweaning influence of elevated masticatory loads because of increased jaw-adductor muscle and bite forces on the biomineralization of mandibular cortical bone and dental tissues. Microcomputed tomography (microCT) was used to quantify bone density at a series of equidistant external and internal sites in coronal sections for two symphysis and two corpus locations. Discriminant function analyses and nonparametric ANOVAs were used to characterize variation in biomineralization within and between loading cohorts. Multivariate analyses indicated that 95% of the myostatin-deficient mice and 95% of the normal mice could be distinguished based on biomineralization values at both symphysis and corpus sections. At the corpus, ANOVAs suggest that between-group differences are due to the tendency for cortical bone mineralization to be higher in myostatin-deficient mice, coupled with higher levels of dental biomineralization in normal mice. At the symphysis, ANOVAs indicate that between-group differences are related to significantly elevated bone-density levels along the articular surface and external cortical bone in the knockout mice. Both patterns, especially those for the symphysis, appear because of the postweaning effects of increased masticatory stresses in the knockout mice versus normal mice. The greater number of symphyseal differences suggest that bone along this jaw joint may be characterized by elevated plasticity. Significant differences in bone-density levels between normal and myostatin-deficient mice, coupled with the multivariate differences in patterns of plasticity between the corpus and symphysis, underscore the need for a comprehensive analysis of the plasticity of masticatory tissues vis-à-vis altered mechanical loads.

Phenotypic Plasticity and Function of the Hard Palate in Growing Rabbits

“…Therefore, findings from this study indicate that morphological differences between dietary cohorts reflect adaptive osteogenic responses for maintaining the structural integrity of the hard palate vis-à -vis altered masticatory stresses. The differentially greater variation in palate cortical thickness and bone area further reinforce the significance of such parameters of internal geometry for interpreting the variation and plasticity of skeletal tissues in extant and extinct taxa (Daegling, 1989;Nicholson et al, 2006;Ravosa et al, 2007aRavosa et al, ,b,c, 2008a.…”

“…For instance, among Plio-Pleistocene hominins, Paranthropus is distinguished by a heavily developed masticatory complex widely considered as adapted for producing and countering increased masticatory stresses associated with hard and/or tough food items (Tobias, 1967;du Brul, 1977;Walker, 1981;Rak, 1983;Demes and Creel, 1988;Hylander, 1988;Daegling, 1989;Constantino and Wood, 2007). Current understanding of the primate face from experimental data supports assertions that this region is under strong selective pressures related to masticatory activity (Hylander, 1979a(Hylander, ,b,c, 1988(Hylander, , 1992Hylander and Johnson, 1997;Ravosa et al, , 2007aRavosa et al, ,b, 2008a. The hard palate of Paranthropus, which is relatively ''deep'' or superoinferiorly tall, further characterizes the genus when compared with its sister taxon Australopithecus (Ward and Kimbel, 1983;McCollum et al, 1993).…”

“…Intra-and between-group variation in palatal form was assessed via microCT (Nicholson et al, 2006;Ravosa et al, 2007aRavosa et al, ,b,c, 2008a. The Siemens microCAT II X-ray tube was operated at 80 kV and 500 mA, with reconstruction using 0.103 mm 3 voxels (volume elements).…”

“…plasticity among cranial regions as well as to control for subtle size-related variation in the skull and masticatory apparatus in comparisons of loading cohorts (sensu Bouvier and Hylander, 1981, 1982Nicholson et al, 2006;Ravosa et al, 2007aRavosa et al, ,b,c, 2008a. Gross and microCT inspection confirmed early fusion of the midpalatal suture in rabbits (Persson and Roy, 1979), with extensive obliteration at 4.5 months old prohibiting a functional analysis of sutural interdigitation in this sample.…”

Life history as a constraint on plasticity: developmental timing is correlated with phenotypic variation in birds

“…Across vertebrates, mechanical stress has been shown to have a pronounced influence on both muscle and skeletal development (Turner, 1998;Moore, 2003;Ruimerman et al, 2005;Ravosa et al, 2007;Ravosa et al, 2008), in particular for jaw and craniofacial structures. For example, fish reared on different diet types develop entirely different jaw morphologies (Meyer, 1987;Wainwright et al, 1991;Adams et al, 2003;Muschick et al, 2011), which adaptively affects their feeding performance on locally abundant resources (Bouton et al, 2002;Parsons and Robinson, 2007).…”