Focal adhesion kinase and ARHGAP26 in cardiac and skeletal muscle development

Cardiac and skeletal muscle are highly specialized tissue types and the normal development of these striated muscles during embryogenesis requires very tightly regulated processes such as cell-type specific proliferation, expression of relevant marker genes, and formation of functional sarcomeres. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase which has been shown in various model systems to regulate processes required for both cardiac and skeletal muscle development. While FAK has been shown to regulate late-phase cardiogenic steps such as ventricular septation and cardiac compaction, it is currently unknown whether FAK regulates earlier steps of cardiogenesis. In order to address this possibility, we utilized an antisense morpholino strategy to deplete FAK during frog embryogenesis. The data described herein demonstrate that FAK morphant embryos exhibited markedly diminished cardiomyocyte proliferation in pre-looped heart tubes and that these heart tubes failed to fully undergo looping morphogenesis. FAK interacts with a variety of binding partners including ARHGAP26, which is also referred to as, GTPase activating protein for Rho associated with FAK, (Graf). This Rho-specific GAP protein has been demonstrated to regulate actin cytoskeleton dynamics and is known to be expressed in terminally differentiated tissue types. However, very little is known about what role Graf might play during embryogenesis. Herein we demonstrate that Graf is expressed during frog embryogenesis in a variety of tissue types including heart, brain, and somites. Utilizing an antisense morpholino approach, we establish for the first time that Graf is required during embryogenesis since all Graf-deficient embryos died during tadpole stages. Furthermore, Graf morphant embryos exhibited cardiac dysmorphogenesis and aberrant somite formation leading to a dystrophic phenotype resulting in swimming defects and paralysis. Our studies indicate that Graf depletion leads to markedly decreased muscle marker gene expression, aberrant sarcomere formation, and disruption of cellular attachments to the extracellular matrix. Taken together, the data provided in this dissertation greatly enhance our understanding of the roles of FAK and Graf in regulating the proper development of both the heart and skeletal muscle during embryogenesis