Growth allometry of the mandibles of giant transgenic mice: an analysis based on the finite-element scaling method

Transgenic mice genetically engineered to produce increased levels of growth hormones, accelerated somatic growth, and larger terminal sizes [Palmiter et al., 1982, 1983] offer an intriguing model with which to investigate the genetic and developmental control of skeletal proportions. In this study, form differences in the mandible between giant transgenic mice (MT-rGH) and their normal litter-mate controls are examined using data generated by finite-element scaling analysis (FESA). Finite-element scaling analysis is a tensor based method developed to study morphological differences between forms. The method uses landmark data to provide measures of size and shape differences local to those landmarks of mandibular size and shape differences for 18 landmarks were compared between the two mouse samples. Bivariate and multivariate analyses were completed to ascertain 1) whether the mandible of larger transgenic mice differed significantly from normal controls, and 2) if observed proportion change resulted from the general allometric affects of overall mandibular size increase. Comparisons of local size and shape differences against a measure of total size difference reveal similar trajectories of growth allometry, indicating that proportion differences between adult control and transgenic mice result from ontogenic scaling.