Meeting Abstract

45.4  Saturday, Jan. 5  Investigating the Lateral Somitic Frontier in the Mouse and Chick Scapula Using 3D Modeling SHEARMAN, R.M.*; TULENKO, F.J.; WINSLOW, B.B.; SFERLAZZO, M.; BURKE, A.C.; Wesleyan University; Wesleyan University; Wesleyan University; Wesleyan University; Wesleyan University rshearman@wesleyan.edu

All limbed vertebrates have a pectoral girdle bridging the somite-derived axial column with the lateral-plate-derived fore-limb skeleton. Although the shoulder is part of the appendicular skeleton, the avian scapular blade is derived primarily from somitic mesoderm (SM) and only the scapular head and neck form from lateral plate mesoderm (LPM). The interface between LPM and SM (the lateral somitic frontier, LSF) defines two domains: (1) the primaxial domain consists of SM-derived muscle, bone, and connective tissue, and (2) the abaxial domain includes muscle and bone that develop within LPM-derived connective tissue. We have mapped the frontier in transgenic mice that activate Cre recombinase driving alkaline phosphatase specifically in the LPM, and we visualized the LSF using Amira^TM 3D reconstruction software. Our data show that only the vertebral margin of the mouse scapula is primaxial, and the remaining bulk is abaxial. We are also investigating the position of the LSF in the avian shoulder. In chicks, the frontier may be coincident with the boundary between somitic and lateral plate components of the scapula. Alternatively, connective tissue from the LPM may invest portions of the SM-derived scapula displacing the frontier distally along the blade. To address this, we are transplanting stage-matched presomitic mesoderm of quail into chick hosts. Graft reconstructions will allow us to visualize quail tissue in 3D and locally map the position of the frontier. We believe that the abaxial and primaxial domains represent two distinct embryonic patterning environments, and positional differences in the frontier across species will correlate with specific evolutionary changes in the vertebrate body plan.