DiGeorge Project

DiGeorge syndrome (DGS) is the most common congenital deletion syndrome in humans, and is based on haploinsufficiency of a 3Mb region on human chromosome 22q11. Children with VCFS/DGS present with a spectrum of phenotypes including cardio-vascular defects, thymus aplasia, muscle weakness, hypernasal speech and learning disabilities. A candidate gene, Tbx-1, has been identified, and inactivation of this gene in mouse leads to many of the characteristic phenotypic features of DGS. However, it has become increasingly clear, that additional genes can cause or influence the severity of DGS. In order to identify those DGS-associated genes, we collaborate with the groups of Raju Kucherlapati and Len Zon (both at Harvard Medical School). In this project we make use of a zebrafish model for DGS, the mutant vanGogh (vgo), which has a Tbx-1 mutation. Here, we use a combination of microchip gene array to identify genes that are differentially expressed between vgo mutants and wildtype embryos. We study these genes by in-situ hybridization to identify expression patterns of interest (i.e. expression in organs such as ear, heart and arches, which are affected in DGS patients and vgo), thus narrowing down potential candidate genes that may be involved in the Tbx-1 pathway. We then transiently inactivate candidate genes using Morpholinos, and use over-expression/ rescue studies to imitate or suppress the Tbx-1 mutation, respectively. Genes that fulfill all the criteria (differential expression in tissues of interest, inactivation phenocopies aspects of DGS, over-expression rescues aspects of DGS) will be inactivated in mouse by a knock-in strategy for a more detailed analysis of gene function in isolated mammalian tissues. An example of two genes identified in this way are shown in the Figure (NCC = neural crest cells, RBc = Rohon-Beard cells, E = eye, T = trigeminal nerve, N = notochord, OV = otic vesicle).