Expression and Function of Paxillin Genes in Zebrafish: A Role in Skeletal Muscle Development

Abstract

Paxillin is a key component of the Integrin adhesion complex, which regulates cellular signaling events in response to extracellular matrix interactions. Although the roles for Paxillin in cell migration have been extensively studied, less is understood about its role in vertebrate development. Depletion of Paxillin from mouse embryos results in early lethality due to impaired cardiovascular development and function, necessitating the development of alternative vertebrate genetic models for examining the role of Paxillin during embryogenesis. Zebrafish have emerged as an experimental vertebrate model amenable to genetic manipulation. The work compiled herein first characterizes the expression profiles for Paxillin genes in zebrafish, and then describes the embryonic phenotypes observed upon mutation of these genes. The identification of two Paxillin genes in zebrafish, pxnaand pxnb, provided new insight into the evolution of this gene family in the Teleost lineage. Both overlapping and unique expression profiles for these genes during zebrafish embryogenesis were uncovered. While both genes are expressed in developing skeletal muscle, pxnawas restricted to the notochord during earlier stages of embryogenesis and pxnbwas expressed in the developing heart. Targeted mutation of either gene alone did not impair embryonic development, suggesting partial functional redundancy between each gene during embryogenesis. Accordingly, combined mutations in pxnaand pxnbrevealed defects during the development ofseveral embryonic tissues. In particular, skeletal muscle morphogenesis iiiwas perturbed in these double mutant embryos. Further characterization revealed that Paxillin genes in zebrafish serve to regulate embryonic myotome shape and proper extracellular matrix composition during muscle development. The amount of Laminin was reduced, while the abundance of Fibronectin persisted, during myotome morphogenesis in Paxillin double mutant embryos. In addition, a role for cytoskeletal contractility in regulatingsubcellular localization of Paxillin in developing skeletal muscle was established. Defects in the development of the cardiovascular system were also apparent in Paxillin double mutant embryos, and future work will focus on characterizing these in further detail. Altogether, this work provides a new vertebrate model to use for understanding the role of Paxillin during embryonic development, and uncovers an unrecognized role for Paxillin in establishing the extracellular matrix of skeletal muscle.