Investigating the role of DOCK6 and EOGT in cardiac development and congenital heart disease

Congenital Heart Defects (CHDs) are structural malformations that occur during development and affect around 1% of live births worldwide. Correct heart development requires tight spatiotemporal control of both the RAC1/CDC42 and NOTCH signalling pathways, and mutations in components or regulators of both pathways can lead to CHDs. Adams-Oliver Syndrome (AOS) is a multisystemic disorder in which 20% of patients also suffer from CHDs. All known causative mutations in AOS have been identified in RAC1/CDC42 or NOTCH signalling pathway components, including autosomal recessive mutations in DOCK6 and EOGT which regulate RAC1/CDC42 and NOTCH signalling respectively. However, it is unknown how mutations in these genes lead to the onset of this disease. I aim to understand how mutations in DOCK6 and EOGT lead to dysregulation of RAC1/CDC42 and NOTCH signalling during heart development and cause CHDs in patients with AOS, using zebrafish as a model.

I find that mRNA of both dock6 and eogt is expressed transiently during early zebrafish cardiovascular development. eogt mRNA expression is restricted to a subset of developing vascular structures, while dock6 exhibits slightly broader expression. Unexpectedly, both genes also have non-coding transcripts which are expressed in the myocardium during early heart morphogenesis: a dock6-RI1 retained intron transcript and an eogt-201 antisense transcript. Using CRISPR mediated genome editing I have created zebrafish models of AOS with mutations in both dock6 and eogt, in which I assess cardiac morphology throughout development. In addition, I investigate whether non-coding transcripts of dock6 and eogt play a role in heart development, or the onset of CHDs in AOS patients. Finally, I investigate a cell intrinsic compensation mechanism identified in human cells which activates RAC1/CDC42 in the absence of DOCK6 and assess whether this compensation mechanism could be active in dock6-RI1 retained intron mutants which have reduced dock6 expression.