Meeting Abstract

P2.41  Monday, Jan. 5  Mechanical and Mesenchymal Mechanisms of Secondary Chondrogenesis SOLEM, R. Christian*; EAMES, Brian F; TOKITA, M; SCHNEIDER, Richard A; Harvard University; University of Oregon; Kyoto Univeristy; University of California, San Francisco rcsolem@gmail.com

Secondary cartilages, which arise after formation of the primary cartilaginous skeleton and during later stages of osteogenesis, are found within joints, ligaments, and tendons. Secondary cartilages facilitate skeletal movement and much evidence suggests their induction requires mechanical stimulation. Thus, the evolutionary presence or absence of such cartilage reflects species-specific variations in functional anatomy. To investigate molecular, cellular, and biomechanical mechanisms that regulate secondary cartilage formation, we conduct experiments using quail and duck, which exhibit distinct jaw morphologies and modes of feeding. Duck use levered straining and have a prominent secondary cartilage at the insertion of the jaw adductor muscle. An equivalent cartilage is absent in quail, which peck at their food. We hypothesize that differences in jaw morphology and the local mechanical environment promote secondary chondrogenesis in duck versus quail. As a test of our hypothesis, we employ two experimental approaches. First, we alter the mechanical environment in embryonic duck by paralyzing skeletal muscles and by blocking mechanotransduction through stretch activated channels. Second, we re-pattern the duck jaw complex to resemble that found in quail by transplanting neural crest mesenchyme destined to form skeletal and connective tissues of the jaw. This mesenchyme is known to generate species-specific pattern. Both approaches inhibit secondary cartilage formation by altering expression of genes required for cartilage, bone, muscle, and tendon development. We conclude that mesenchyme-dependent changes in gene expression, musculoskeletal pattern, and mechanical forces control secondary cartilage induction.