Ware Lab

  • Genetic Causes of Heterotaxy / Congenital Heart Disease

    A number of causative genes have been identified in patient populations at increased risk for heterotaxy; however, mutations in individual genes are detected with low frequency and, together, likely explain only a small percentage of heterotaxy cases. This heterogeneity is underscored by the presence of microdeletions, aneuploidy and other complex chromosomal rearrangements (translocations, inversions, terminal deletions) in some patients with laterality defects.

    Analysis of genes located within submicroscopic chromosomal imbalances promises to be a particularly useful tool in uncovering novel genes and pathways connected to heterotaxy and congenital heart disease. We are undertaking research in this area using the African clawed frog (Xenopus) to study the developmental influence of submicroscopic copy number variants (CNVs) detected by whole genome genotyping in patients with heterotaxy. We are performing gain- and loss-of-function analyses of heterotaxy candidate genes as appropriate for detected duplications and deletions.

    Xenopus offers a number of advantages as a model system for left-right patterning, demonstrating strong conservation of pertinent biological pathways, and the ability to study laterality lineage markers in a moderate-throughput, low-cost system. Xenopus eggs are large, plentiful and fertilized externally, simplifying embryo handling and genetic manipulation. Furthermore, the three chambered Xenopus heart more closely approximates the four-chambered mammalian heart than other non-mammalian model organisms such as zebrafish, providing a valuable opportunity to study the etiology of many of the congenital heart defects associated with heterotaxy.
 
  • Abnormal outflow tract and valves in a mouse heterotaxy model at embryonic day 12.5.

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    Abnormal outflow tract and valves in a mouse heterotaxy model at embryonic day 12.5.

    Abnormal outflow tract and valves in a mouse heterotaxy model at embryonic day 12.5.

  • Xenopus embryos are used for functional analysis of candidate genes.

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    Xenopus embryos are used for functional analysis of candidate genes.
    Xenopus embryos are used for functional analysis of candidate genes.
  • Whole mount in situ hybridization (WISH) of WT Xenopus embryos to visualize expression of marker genes cardiac troponin (top - arrowhead) and Pitx2 (bottom - arrowhead).

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    Whole mount in situ hybridization (WISH) of WT Xenopus embryos to visualize expression of marker genes cardiac troponin (top - arrowhead) and Pitx2 (bottom - arrowhead).
    Whole mount in situ hybridization (WISH) of WT Xenopus embryos to visualize expression of marker genes cardiac troponin (top - arrowhead) and Pitx2 (bottom - arrowhead).  Troponin WISH allows for easy visualization of the direction of heart looping, which is often reversed when left-right patterning is disturbed.  Pitx2 is normally expressed in left lateral plate mesoderm, as shown, but is often expressed bilaterally or on the right side when left-right patterning is disturbed.