Meeting Abstract
123.7 Tuesday, Jan. 7 15:00 Comparative studies on the ontogeny of the primary palate and nasal cavities in birds and mammals ABRAMYAN, J*; CHENG, J; RICHMAN, JM; University of British Columbia; UBC; UBC abramyan@dentistry.ubc.ca
A critical period in craniofacial ontogeny involves the proper development of the primary palate and nasal cavities. Nasal cavities initiate as external nasal pits which grow dorsally and connect with the oral cavity via paired choanae. However, this developmental process has diverged between mammalian and reptilian (including birds) embryos. A key characteristic of choana development in mammals is the presence of a transient oronasal membrane which initially separates oral and nasal cavities and subsequently ruptures during developmental progression. The breakdown of this membrane is essential for respiration and ultimate survival. Interestingly, the presence of this membrane in non-mammalian amniotes is still a contentious subject in the literature. This is compounded by the scarcity studies of primary palate formation in reptiles. In this study, we used optical projection tomography and histology to obtain 3D reconstructions of the nasal cavities and associated choanae in chicken and mouse embryos. We found that avian embryos do not form an oronasal membrane. Instead, the outgrowing frontonasal and maxillary processes leave a groove between them which connect the oral and nasal cavities. Furthermore, we measured relatively lower cellular proliferation in the mesenchyme at the base of invaginating groove and higher proliferation within the outgrowing processes. The groove remains while the facial processes outgrow and subsequently fuse, leaving a choanal tube connecting the external nares to the oral cavity. These results, along with a similar choanal development described in amphibians, suggest that the formation of a groove is the basal condition in vertebrates and that mammals have derived a divergent ontogenetic process for the development of the primary palate and connection of external nares to the oral cavity.
