A biphasic role for the voltage-gated sodium channel scn5Lab in cardiac development of zebrafish

Abstract

A BIPHASIC ROLE FOR THE VOLTAGE-GATED SODIUM CHANNEL SCN5LAB IN CARDIAC DEVELOPMENT OF ZEBRAFISH

JEFFREY S. BENNETT

Dissertation under direction of Professor Dan M. Roden, M.D.

Voltage-gated sodium channels (VGSCs) play an important role in generation and propagation of action potentials in nervous and cardiac tissues. Less is known of a possible role for them in development of the heart. Homozygous deletion of the voltage-gated sodium channel Scn5a results in embryonic lethality and developmental defects in the mouse heart. Morpholino knockdown of the two cardiac VGSC isoforms in zebrafish, scn5Laa and scn5Lab, results in small dysmorphic ventricles and death by four days post-fertilization. Here, I examine a role for scn5Lab in multiple phases of cardiac development. I find that loss of scn5Lab results in impaired specification of pre-cardiac mesoderm, with specific loss of the cardiac transcription nkx2.5. Differentiation of myocardium from the second heart field is determined to be intact, genetically and morphologically. Further I find that proliferation of differentiated cardiomyocytes is absent in morpholino-injected embryos, an effect that appears to be independent of impaired cardiac function. Electrophysiologic studies suggest voltage-gated sodium channels are present, but not required for action potentials at this time. I conclude that scn5Lab has a biphasic role in cardiac development of zebrafish, likely independent of its role in sodium ion permeation