| Studies of the developmental bases of phenotypic variation are critical for a deep understanding of the evolutionary origins of traits that define the primate clade and the human lineage. This work focuses on the poorly studied role that blood-vessel branching and growth (angiogenesis) plays during craniofacial bone formation and mineralization (osteogenesis). We hypothesized that angiogenesis dysregulation can produce evolutionarily relevant variation of the craniofacial complex. Measurements of bone volume and relative density, derived from high resolution computed tomography images of an Fgfr2+/P253R mouse model of Apert syndrome, defined the “normal” pattern of craniofacial bone growth and maturation across the late embryonic period and suggested several hypotheses about the cellular basis of skeletal dysmorphology associated with the Fgfr2 P253R mutation. 3D images of blood vessels and other soft tissue layers associated with the initial intramembranous mineralization of the frontal bone of these mice were generated with a hybrid optical coherence tomography and photoacoustic microscopy system in order to investigate the relationship between invading blood vessels and mineralizing bone. Although the resulting images did not resolve microvasculature or mineralizing frontal bone as we had expected, the results of this work provide the foundation for future studies and suggest that the Fgfr2 P253R mutation may reduce the length of large superficial embryonic blood vessels of the head. Finally, the craniofacial skeletal phenotypes of mice that conditionally express this mutation in endothelial cells were quantified in order to determine if endothelial expression is associated with the craniofacial dysmorphology noted in the Fgfr2+/P253R mice. A combination of landmark based and volume/relative density based analyses suggested that endothelial expression of the mutation is associated with overall reduced scale of the skull. We hypothesized that this reduction is based on reduced endothelial sprouting during the angiogenesis associated with initial mineralization of craniofacial bones. In total, this work introduces refined methods to quantify important phenotypic aspects of the craniofacial complex and provides evidence that dysregulation of angiogenesis can serve as the indirect basis of craniofacial skeletal dysmorphology. This, in turn, suggests the importance of angiogenesis regulation in producing evolutionarily relevant skeletal variation found in our evolutionary past. |
