Molecular Mechanisms of Transcription Factor Dosage in Heart Development and Congenital Heart Disease
Abstract
Congenital heart defects are present in 1-2 out of 100 births and are the leading non-infectious cause of death in the first year of life. Holt-Oram syndrome is an inherited disorder, characterized by congenital heart defects and upper limb defects. Holt-Oram syndrome is caused by inheritable genetic mutations in a gene called TBX5. The TBX5 gene makes a master gene regulator, a protein that turns on or off other genes by virtue of its ability to bind DNA sequences with a specific signature. TBX5 mutations are thought to reduce the TBX5 protein levels by half, but we don’t know how this partial loss of TBX5 protein causes heart or limb defects. Understanding where in our genome TBX5 acts to turn on or off genes important for formation of the heart or limbs is essential to begin to develop therapies for these congenital defects. In addition to the relevance to congenital heart and limb defects, the knowledge of the cues that are normally used to build the heart could be harnessed to regenerate damaged hearts. Our project aims at understanding how TBX5 works to control cardiac genes and how its function is disrupted in congenital heart disease. To do so, we first will identify all the sites in the genome of embryonic heart tissue where TBX5 is present. This will let us know what genes it is likely to be acting upon. We will also examine partner proteins for TBX5, which may provide clues about how TBX5 reaches its specific target sites in the genome. Then we will examine what happens to TBX5 when there is a mutation that causes a 50% loss of TBX5 protein. Do all the sites where TBX5 normally goes to experience a 50% drop in TBX5 presence, or are there specific places that are sensitive to the levels of TBX5? What happens to TBX5’s partner proteins? And how does this relate to changes in gene expression in the malformed hearts and limbs? This information will guide us toward an understanding, currently lacking, of why a 50% reduction in levels of a master regulator factor like TBX5 results in birth defects. Finally, we will investigate how cells of the mouse heart behave when there is a reduction in TBX5 levels. Our current data show that cells line up very precisely in the region of the heart that separates the left and right sides of the heart and that partial reduction of TBX5 levels causes a mixing of the cells and subsequently heart defects (hole in the heart). We explore what happens to the cells at this boundary and how TBX5 might be involved in helping them line up so precisely. Overall, our experiments will bring considerable new knowledge to light about how genes are regulated in the formation of the heart and how mutations in genes such as TBX5 cause congenital heart defects. In the short term, this knowledge will be valuable to understand the basis of these birth defects and perhaps to devise strategies to identify them before they occur or even to try to treat them before they develop. In the long term, we hope to be able to identify treatments for various kinds of heart defects and also to use the information learned about how hearts are normally made, to devise ways to regenerate damaged hearts, for example, after a heart attack.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1710191
Entities
People
- Benoit Bruneau
Organizations
- The J. David Gladstone Institutes
- United States Army