Kids Kidney Research - Why do individuals with DiGeorge Syndrome often have kidney malformations?

Why do individuals with DiGeorge Syndrome often have kidney malformations?

DiGeorge syndrome presents with heart defects, palatal anomalies, low blood calcium, and problems with the immune system. These defects are known to be caused by a deficiency of the gene Tbx1 (pronounced ‘tea-bee X one’), which produces a protein whose role during development is to switch other genes on. As many as one third of people with DiGeorge syndrome are born with structural abnormalities of the urinary tract and kidneys, and some of them will have quality of life compromised by failing kidney function. The aim of the project is to establish whether Tbx1 is ‘active’ in the kidney before birth and whether a lack of Tbx1 makes a contribution to these kidney malformations. If a preliminary study shows that Tbx1 is indeed involved in kidney development, further funding will be sought to work out exactly how it directs normal growth of the kidney before birth.

Final project report prepared by Professor Adrian Woolf on 11 December 2007

Summary of Results

We have performed a detailed analysis of expression of the Tbx1 gene during normal renal tract development in mice. To assess expression of messenger RNA, we used reverse transcription polymerase chain reaction on different stages of mouse development. Using this method we showed that the gene was indeed active at the start of embryonic kidney development and also at later stages of renal tract pre-natal maturation. These mouse anatomical stages are approximately equivalent to human fetuses of between 7 to 20 weeks gestation. We also made a detailed study of exactly where the Tbx1 protein is found using the technique of immunohistochemistry. At the very initiation of the kidney, the protein can be seen in nuclei of the ureteric bud, which will later form the ureter and kidney collecting ducts. The nuclear localisation is consistent with the fact that the Tbx1 gene acts as a transcription factor, directing the expression of other nephrogenesis genes. As the embryonic kidney differentiated, Tbx1 protein was also found in the nuclei of diverse epithelia including tubules and glomeruli. In addition, Tbx1 protein was also seen in nuclei of diverse other organs affected in DiGeorge syndrome including the branchial arch epithelium and heart muscle cells; it was also seen in epithelial cells of the developing lung, ear and teeth. Interestingly, using both RNA and protein analyses, the Tbx1 gene was also found to be expressed in mature mouse kidney, suggesting that it has roles in maintaining the health of the adult kidney, as well as directing the differentiation of the organ.

Planned future work and outputs:

The above data confirm that the Tbx1 gene is active in renal tract development and these new observations are consistent with the facts that kidney and ureter malformations are sometimes seen in individuals with DiGeorge syndrome. We think that the data will be sufficient for a modest research paper. However, in the next few months, we aim to continue this line of work to assess renal tracts of mice with mutations of the Tbx1 gene. This aspect will make the expression data more interesting. At that point, it may well be possible to extend the research by applying for a larger grant e.g. from Kidney Research UK, or other funding bodies.