Meeting Abstract

P1.57  Jan. 4  The Lateral Somitic Frontier in the Mouse DURLAND, J.L.*; SFERLAZZO, M.; BURKE, A.C.; Wesleyan University; Wesleyan University; Wesleyan University jdurlandster@gmail.com

We have mapped the interface between somitic and lateral plate (LP) mesoderm in the mouse using available transgenic lines. We crossed Prx1Cre and Z/AP mice (Logan et al., 2002) to produce embryos where alkaline phosphatase is expressed only in cells of the LP. Visualization of LP cells over time allowed us to examine the dynamics of two mesodermal domains, one composed entirely of somitic cells (primaxial), and one containing migratory somitic myoblasts within LP connective tissue (abaxial). The boundary between primaxial and abaxial domains is called the lateral somitic frontier (LSF). At early stages the LSF is uniform along the anterior-posterior (AP) axis. Over time, the AP contour of the LSF varies with the degree of expansion of the primaxial domain at different levels. At later stages, the frontier is strikingly discontinuous and bisects several anatomical structures. Abaxial portions of the spinotrapezius m., latissimus dorsi m., and certain spinal nerves are observed close to their origins, deep within surrounding primaxial tissue. The scapula is abaxial except for the primaxial vertebral border. In the pelvis, the most lateral cells of the sacral ribs are LP-derived, the rest of the bone is somitic in origin. Discontinuity in the frontier becomes apparent between 13.5 dpc and 15.5 dpc, suggesting that during relative expansion of the primaxial domain, the abaxial regions of certain musculoskeletal elements are exposed. The LSF seems to represents a �cryptic boundary�, without apparent significance for adult function, but with clear significance during development. We believe the LSF plays an important role in global patterning of the musculoskeletal system. Logan, M., Martin, J.F., Nagy, A., Lobe, C., Olsen, E.N., and Tabin, C.J. 2002. Genesis 33(2): 77-80.