The quantitative and qualitative analysis of the craniofacial skeleton of mice lacking the IGF-I gene

Insulin-like growth factors are mediators of growth hormone and are believed to also stimulate growth independently. Insulin-like growth factor I (IGF-I) null mutant mice exhibit a lower rate of skeletal growth compared with their wild-type (control) littermates. Although their general body dimensions seem proportionate, their heads appear shortened with a blunt nose compared with the controls. The aim of this project was threefold: 1) to investigate whether differences in shape/form exist between the craniofacial skeleton of the IGF-I null mutant mice and their control littermates by using three techniques; 2) to determine whether the three techniques yield similar, different, or complementary information regarding the size and shape of specimens; and 3) to investigate whether the histological sections obtained from the craniofacial skeleton exhibit any differences between the two groups. Thirty adult male mice, 12 mutant and 18 wild type, obtained from 11 litters were examined. Lateral and superio-inferior radiographs of their head were analyzed by the procrustes, the macroelement, and the traditional cephalometric techniques. Later, the animals were processed for routine histological examination. The IGF null mutant mice demonstrated a generalized decrease of craniofacial size (43-64% of the normal adult size) and a non-allometric change of shape when compared with their wild-type littermates. While the mandible did not exhibit any shape changes, the facial and cranial areas demonstrated prominent changes. Examination of histological sections did not reveal any structural difference between the two groups at the adult stage. Furthermore, procrustes and macroelement techniques offer a more complete, detailed, and comprehensive description of the specimens compared.