The Functional Roles of Zebrafish Irx1a Gene in Heart Development and Regeneration

Precise conduction control is required for the anatomical and electrical components of the heart to work seamlessly to deliver coordinated mechanical contractions. The cardiac conduction system (CCS) in turn relies on correct patterning of ion channels whose expression is under control of the cardiac transcription factors (TF). Incorrect patterning or mutations of the ion channel genes result in major heart problems. How the cardiac TF interact with each other in controlling the spatial and temporal expression of ion channel genes is poorly understood. The zebrafish provides several unique advantages as a model organism for studying vertebrate cardiovascular development and diseases. The transparent embryos, together with transgenic technology, allow direct observation of heartbeat and blood circulation by imaging in live embryos under optical and fluorescence microscopy. The ease of genetic manipulation makes mechanistic investigations feasible in a relatively short period of time. The adult zebrafish heart can regenerate completely in 21 days without scar formation after heart injury. In addition, the zebrafish is capable of robust regeneration. My laboratory has recently obtained some exciting data on a gene calledirx1a. Loss-of-function ofirx1ain early embryos led to abnormal cardiac development and perturbed electrophysiology. In the absence ofirx1a, the expression of the voltage-gated sodium ion genescn5Laawas mostly abolished while the expression of the cardiac TFtbx5.1was down-regulated. Furthermore, we found thatirx1ais up-regulated in the leading edge of the amputated adult heart as early as 3 days-post-amputation (dpa), suggesting a potential role of this gene in the early events of heart regeneration. Taken together, our preliminary data suggest a critical role forirx1ain zebrafish heart development and regeneration. In this project, we will confirm thatirx1aindeed controls ion channel gene expression during embryonic heart development and in regenerating adult heart. Our study will also positionirx1ain the regulatory hierarchy of cardiac TF controlling ion channel gene expression, which is essential in establishing a functional conduction system in the developing embryonic heart and the regenerating adult heart. In addition, we will delineate the role(s) ofirx1ain the morphological and physiological recovery during heart regeneration. The proposed studies will contribute to our understanding on how to skewer the molecular pathway from scar formation to tissue regeneration after injury, therefore highly relevant to human diseases. This system can also be applied to screening for drugs or small molecules with therapeutic potentials on heart injury.