Genetic Modifiers of Cardiac Development 22q11DS Mouse Models

Abstract

Over 70% of patients with 22q11.2 Deletion Syndrome (22q11DS) have congenital heart defects. The prevalence and severity of these defects make it critical for us to strive to understand the underlying mechanism of the syndrome by elucidating the gene pathways that are involved in heart development, as their disruption may lead to congenital heart diseases (CHDs). TBX1 and CRKL, the main genes that have implicated in 22q11DS as responsible for patient CHDs, are required for normal development of the heart. It's been suggested that some genes located outside of the 22q11 deleted region can act as genetic modifiers of CHDs in the syndrome and may also be required for normal development of the heart. Three of these genes are NTRK3, WNT5A and ROR2. Mutations in WNT5A and ROR2 were identified in patients with CHDs and 22q11DS, while mutations in NTRK3 were identified in non‐syndromic patients with CHDs. One of the overarching aims of this study is to test whether genetic modifiers of heart defects associated with the 22q11.2 deletion are the same genes as the genes that alter risk for heart defects in non‐syndromic CHD patients. First, we must test where these three genes are expressed in normal developing embryonic hearts and we have decided to use the mouse as a model to do this. Digoxigenin‐labeled RNA probes for Ntrk3, Wnt5a and Ror2 were designed and used for in situ hybridization in order to observe the expression of these genes in mouse embryos specifically in the heart and regions that contribute to the formation of the heart. Ntrk3, Ror2 and Wnt5a were expressed in the pharyngeal arches and heart region. The expression of the genes Ntrk3, Ror2 and Wnt5a were not only restricted to the heart regions but were also seen in the neural tube area. We also examined the expression of Ror2 in Crkl knock‐out embryos, but observed no change. The results may support our hypothesis that NTRK3, WNT5A, and ROR2 may be causative of CHDs, since they were found to be expressed in the heart and regions required for heart development, however, more work is needed to prove this. More work is also needed to show whether any of these genes act in the same pathway as genes in the 22q11 deleted region to function in normal heart development.