Cardiac phenotyping of CHD candidate genes in Xenopus

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DESCRIPTION (provided by applicant): Congenital heart disease (CHD) occurs in approximately 8 out of 1000 live births and effects 1.3 million newborns per year worldwide. While there is evidence to indicate that CHD does have a genetic basis, most of CHD burden remains unexplained genetically. New genomics technologies can efficiently identify variations in the genomes of CHD patients, but only a small percentage have second unrelated alleles to validate them as disease causing. Therefore there is a pressing need to develop functional assays to evaluate these candidate genes for CHD. There are two main goals for these functional assays: 1) provide evidence supporting candidate genes as disease causing and 2) identify the mechanism for the candidate gene on normal development and the disease state. Here we develop Xenopus as a rapid model system for testing CHD genes and apply advanced optical imaging methods to detect cardiac phenotypes. Xenopus is as an important animal model of congenital heart disease: large numbers of embryos can be readily manipulated, protein expression can be knocked-down using antisense morpholino oligos, and the heart is easily visualized. To expand the CHD spectrum that can be modeling in Xenopus, we need better microscale cardiac imaging methods. During the R21 phase, we will test two technologies, optic coherence tomography (OCT) and our novel hemoglobin contrast subtraction angiography (HCSA) to demonstrate that microscale imaging of Xenopus can be used to screen CHD genomic hits. Optic coherence tomography is an optical imaging system that can capture microscopic structures at high acquisition speeds allowing high-resolution phenotyping of dynamic heart structures. Hemoglobin contrast subtraction angiography (HCSA) is a noninvasive, nondestructive, quantitative microangiographic method that exploits the hemoglobin as an endogenous flow contrast agent during color imaging enabling us to delineate abnormal structures as well as quantify biomechanical phenotypes. In the R33 phase, our overall goal is to apply these methods to facilitate detailed high-resolution structural phenotypin of tadpole hearts that can be used to quickly test CHD candidate genes for cardiac phenotypes. This will allow us to identify cardiac phenotypes in CHD candidate genes that have no previous role in cardiac development and serve as a springboard for future mechanistic studies.