Masticatory HyperMuscularity is not Related to Reduced Cranial Volume in Myostatin-Knockout Mice

Authors

  • James Cray Jr.,

    Corresponding author
    1. Division of Plastic and Reconstructive Surgery, Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania
    2. Pediatric Craniofacial Biology Laboratory, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania
    • Department of Plastic Surgery, Children's Hospital of Pittsburgh, University of Pittsburgh, 3533 Rangos Research Center, 530 45th Street, Pittsburgh, PA 15201
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  • Jared Kneib,

    1. University of Pittsburgh School of Dental Medicine, Pittsburgh, Pennsylvania
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  • Lisa Vecchione,

    1. Pittsburgh Cleft-Craniofacial Research Center, Division of Plastic Surgery, Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania
    2. Department of Orthodontics and Dentofacial Orthopedics, University of Pittsburgh, Pittsburgh, Pennsylvania
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  • Craig Byron,

    1. Department of Biology, Mercer University, Macon, Georgia
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  • Gregory M. Cooper,

    1. Division of Plastic and Reconstructive Surgery, Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania
    2. Pediatric Craniofacial Biology Laboratory, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania
    3. Department of Bioengineering, University of Pittsburgh, Pittsburgh Pennsylvania
    4. Department of Oral Biology, University of Pittsburgh, Pittsburgh Pennsylvania
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  • Joseph E. Losee,

    1. Pittsburgh Cleft-Craniofacial Research Center, Division of Plastic Surgery, Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania
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  • Michael I. Siegel,

    1. Department of Orthodontics and Dentofacial Orthopedics, University of Pittsburgh, Pittsburgh, Pennsylvania
    2. Department of Anthropology University of Pittsburgh, Pittsburgh Pennsylvania
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  • Mark W. Hamrick,

    1. Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, Georgia
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  • James J. Sciote,

    1. Department of Orthodontics, Temple University, Philadelphia, Pennsylvania
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  • Mark P. Mooney

    1. Division of Plastic and Reconstructive Surgery, Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania
    2. Department of Orthodontics and Dentofacial Orthopedics, University of Pittsburgh, Pittsburgh, Pennsylvania
    3. Department of Oral Biology, University of Pittsburgh, Pittsburgh Pennsylvania
    4. Department of Anthropology University of Pittsburgh, Pittsburgh Pennsylvania
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Abstract

It has been suggested recently that masticatory muscle size reduction in humans resulted in greater encephalization through decreased compressive forces on the cranial vault. Following this logic, if masticatory muscle size were increased, then a reduction in brain growth should also occur. This study was designed to test this hypothesis using a myostatin (GDF-8) knockout mouse model. Myostatin is a negative regulator of skeletal muscle growth, and individuals lacking this gene show significant hypermuscularity. Sixty-two [32 wild-type (WT) and 30 GDF-8 -/- knockout], 1, 28, 56, and 180-day-old CD-1 mice were used. Body and masseter muscle weights were collected following dissection and standardized lateral and dorsoventral cephalographs were obtained. Cephalometric landmarks were identified on the radiographs and cranial volume was calculated. Mean differences were assessed using a two-way ANOVA. KO mice had significantly greater body and masseter weights beginning at 28 days compared with WT controls. No significant differences in cranial volumes were noted between KO and WT. Muscle weight was not significantly correlated with cranial volume in 1, 28, or 180-day-old mice. Muscle weights exhibited a positive correlation with cranial volume at 56 days. Results demonstrate that masticatory hypermuscularity is not associated with reduced cranial volume. In contrast, there is abundant data demonstrating the opposite, brain growth determines cranial vault growth and masticatory apparatus only affects ectocranial morphology. The results presented here do not support the hypothesis that a reduction in masticatory musculature relaxed compressive forces on the cranial vault allowing for greater encephalization. Anat Rec, 2011. © 2011 Wiley-Liss, Inc.

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