Integrative and Comparative Biology Advance Access originally published online on April 28, 2008
Integrative and Comparative Biology 2008 48(3):338-344; doi:10.1093/icb/icn020
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Enlargement of the temporalis muscle and alterations in the lateral cranial vault
*Department of Biology, Mercer University, Macon, GA 31201; Department of Orthodontics, School of Dentistry, Medical College of Georgia, Augusta, GA 30912; Department of Surgery, Section of Plastics, Medical College of Georgia, Augusta, GA 30912; Department of Cell Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912
Correspondence: 1E-mail: byron_cd{at}mercer.edu
The purpose of this study was to test the hypothesis that increased masticatory muscle accompanied morphologic changes in the temporal bone and squamosal suture. Ten mice deficient for the protein myostatin (Mstn –/–) had significantly increased skeletal muscle mass and were compared with nine controls (Mstn +/+). Variables measured include linear and areal metrics describing temporal size and temporal bone shape as well as the extent of the area of the squamosal suture that overlaps, or bevels, with parietal bones. Mstn–/– mice showed significantly larger temporalis muscles. Their temporal bones showed significantly decreased size as well as decreased beveling of the squamosal suture. These decreases were absolute as well as relative and were not restricted to either vertical or horizontal axes. The increased masticatory musculature of Myostatin-null mice had a shrinking effect on the temporal aspect of the cranium. These results are inconsistent with the interpretation that increased temporalis mass induces morphologic changes in temporal bone that compensate for putative increases in compressive forces transduced at this region. Rather than increase in the area of overlap between two calvarial bones, potential increase in biomechanical loading along the temporal squama led to a smaller bevel which would presumably weaken this joint. It is unclear why this is so. Either compressive forces are not anabolic to suture beveling or they do upregulate growth of the suture bevel, with compression not being the primary loading regime at this suture.
From the symposium "Building a Better Organismal Model: The Role of the Mouse" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 2–6, 2008, at San Antonio, Texas.