Meeting Abstract

110.6  Sunday, Jan. 6  Craniofacial ontogeny in turtles: the role of bone morphogenetic protein in the loss of palatal shelves ABRAMYAN, J.*; LEUNG, K. J.; MERCHANT-LARIOS , H.; RICHMAN, J.M.; The University of British Columbia; The University of British Columbia; Universidad Nacional Autónoma de México; The University of British Columbia abramyan@dentistry.ubc.ca

Turtles are an enigmatic group of vertebrates whose divergent skull morphology is still at the forefront of scientific discussion. While turtles pass through a conserved stage of primary palate development found in all amniotes, we have found that turtles diverge during secondary palate ontogeny. The typical condition for amniotes is to form outgrowths from the medial sides of the maxillary prominences called palatal shelves. In mammals, the shelves fuse in the midline and form a bony hard palate that completely separates the nasal and oral cavities. In birds and squamates, palatal shelves develop on the lateral sides of the oral roof but remain unfused, leaving a natural cleft. Here, we conclusively excluded the presence of vestigial palatal shelves at any time during the ontogeny of the craniofacial complex in two branches of turtles, a side-necked turtle (Emydura subglobosa) and a sea turtle (Lepidochelys olivacea). Additionally, through comparative analysis of avian and testudine (E. subglobosa) craniofacial gene expression patterns, we have identified a distinct lack of mesenchymal Bone Morphogenetic Protein 2 (BMP2) expression in the maxillary prominences of E. subglobosa. In previous work we showed that when BMP signaling is blocked in the chicken embryo maxillary prominence, a complete loss of palatal shelves occurs. These intriguing avian data suggest that loss of BMP expression in the turtle at an early time in their evolutionary history contributes to the loss of palatal shelves. This work is supported by an NSERC grant to JMR. JA holds an NIH Ruth L. Kirschstein PDF.