Proliferation of embryonic cardiomyocytes in zebrafish requires the sodium channel scn5Lab

Abstract

Summary In mice, homozygous deletion of the cardiac sodium channel Scn5a results in defects in cardiac morphology and embryonic death before robust sodium current can be detected. In zebrafish, morpholino knockdown of cardiac sodium channel orthologs scn5Laa and scn5Lab perturbs specification of pre-cardiac mesoderm and inhibits growth of the embryonic heart. It is not known which developmental processes are perturbed by sodium channel knockdown and whether reduced cell number is from impaired migration of cardiac progenitors into the heart, impaired myocyte proliferation, or both. We found that embryos deficient in scn5Lab displayed defects in primary cardiogenesis specific to loss of nkx2.5, but not nkx2.7. We generated kaede reporter fish and demonstrated that embryos treated with anti-scn5Lab morpholino showed normal secondary differentiation of cardiomyocytes at the arterial pole between 30 and 48 hours post-fertilization. However, while proliferating myocytes were readily detected at 48 hpf in wild type embryos, there were no BrdU-positive cardiomyocytes in embryos subjected to anti-scn5Lab treatment. Proliferating myocytes were present in embryos injected with anti-tnnt2 morpholino to phenocopy the silent heart mutation, and absent in embryos injected with anti-tnnt2 and anti-scn5Lab morpholinos, indicating cardiac contraction is not required for the loss of proliferation. These data demonstrate that the role of scn5Lab in later heart growth does not involve contribution of the secondary heart field, but rather proliferation of cardiomyocytes, and appears unrelated to the role of the channel in cardiac electrogenesis.

Evaluation of the Developmental Toxicity Induced by E804 in Zebrafish Embryos

“…The mRNA expression level of scn5Lab, which is required for zebrafish cardiogenesis, was increased in E804treated group and also indicated that the heart was damaged by E804. Previous reports also shows that pericardial edema, reduction of the heart rate, and smaller of the heart were observed in zebrafish which is deficient in scn5Lab gene (Bennett et al, 2013;Zhu et al, 2019). The decreased fluorescence area and intensity of the liver showed the liver damage in zebrafish larvae exposed to E804.…”

Voltage-gated sodium channels and cancer: is excitability their primary role?

“…These authors observed that the heart tube of zebrafish lacking the ortholog gene SCN5Lab (one of the two orthologs of the SCN5A gene) had less cardiomyocytes than the wild type zebrafish 24 h after fertilization, and that the embryos died before 5 days post-fertilization. Later on, Bennett and collaborators demonstrated that the Na V channel expressed by the SCN5Lab gene is required for the specification of the pre-cardiac mesoderm, and for the proliferation and growth of the developing heart (Bennett et al, 2013 ). The precise mechanism of action is not yet understood but these authors underlined that, as an integral component of cardiomyocytes, Na V could serve non-electrogenic roles by interacting with many partner proteins.…”

HOPX governs a molecular and physiological switch between cardiomyocyte progenitor and maturation gene programs

“…Zebrafish ( Danio rerio ) were maintained at 28°C water temperature and the light cycle was maintained at 14:10 hours (light:dark). We used the zebrafish transgenic line Tg(cmlc2:Gal4-RFP) (Bennett et al, 2013) (also known as Tg(myl7:Gal4) and Tg(cmlc2:GAL4) ). Zebrafish work followed the guidelines of the animal ethics committee at the University of Queensland.…”