Project Summary/Abstract
Appropriate differentiation and maintenance of cellular identity are required for normal development of all organs.
In the heart, mutations in genes that are necessary to maintain cardiomyocyte identity are associated with
structural congenital heart defects, which are the most common malformations found in newborns. Despite their
frequency, the etiology of most congenital heart defects remains poorly understood. Furthermore, numerous
structural congenital heart defects are associated with arrythmias. Although advances in surgical techniques
have been successful in allowing patients to survive to adulthood, the surgeries do not repair arrythmias
associated with the structural defects. Thus, it is essential to understand fundamental mechanisms directing
normal vertebrate heart development, in order to inform us of the etiology of congenital heart defects and their
associated arrythmias. A long-term goal of our lab is to understand the conserved molecular and genetic
mechanisms that direct cardiac chamber size during early vertebrate development. Nr2f transcriptions factors
have highly conserved requirements in vertebrate heart development. Furthermore, mutations in Nr2f genes in
humans are associated with a spectrum of congenital heart defects, including atrial septal defects. This proposal
will investigate fundamental mechanisms determining atrial chamber size through investigating Nr2f-dependent
mechanisms controlling atrial cardiomyocyte differentiation and the maintenance of atrial cardiomyocyte identity.
While requirements for Nr2f factors are well-established in atrial development, the mechanisms controlling Nr2f
gene expression in atrial cardiomyocytes and by which Nr2f transcription factors direct atrial cardiomyocyte
development remain poorly understood. Our work has shown that zebrafish Nr2f1a is the functional equivalent
of Nr2f2 in atrial development. Our preliminary data has identified a conserved enhancer that that is sufficient to
promote Nr2f1a expression in atrial cardiomyocytes zebrafish and that Nr2f1a has a previously unrecognized
requirement concurrently maintaining atrial cardiomyocyte and inhibiting the acquisition of pacemaker
cardiomyocyte identity. In Aim 1, we will interrogate the signals that regulate the conserved nr2f1a cis-regulatory
enhancer that promotes atrial cardiomyocyte expression. In Aim 2, we will determine the temporal requirements
of nr2f1a and the differentiation state of cardiomyocytes within the atria of nr2f1a mutants. In Aim 3, we will
elucidate the Nr2f-dependent gene regulatory networks that repress pacemaker cardiomyocyte identity in venous
atria. Our studies may provide a foundation of information that may inform us of the etiology of congenital heart
defects and their associated arrythmias, which ultimately may lead to novel therapies that can prevent or
ameliorate congenital heart defects and associated arrythmias in humans.