Talk abstracts
Talk on Wednesday 10:00-10:15am submitted by Jenna Thuma
Troponin Enhanceropathies
Jenna Thuma (Biophysics Graduate Program), Yvette Wang (Physiology and Cell Biology), Madhoolika Bisht (Physiology and Cell Biology)
Abstract:
Striated muscle contraction is regulated by the troponin complex which consists of three proteins: troponin C (TnC), troponin I (TnI), and troponin T (TnT). Cardiac troponin’s protein role in the heart is well known and documented; however, we propose a novel role for all three cardiac troponins at the DNA level. DNA regulatory elements are important regions that control cell and time specific gene expression. These types of elements are generally found intergenically or intronically, however, roughly 5-10% are exonic. Shockingly, we found evidence that all three cardiac troponin genes contain exonic DNA regulatory elements. Thus, any nucleotide mutation in their exonic DNA regulatory element could not only change protein structure and function, but also the function of the regulatory element resulting in altered expression of nearby genes. For example, the regulatory element within cardiac TnC is predicted to regulate several genes important for early development and, consistent with this, when we mutate this region we lose all homozygous embryos in both mice and rats. Additionally, the regulatory element within cardiac TnI appears to interact with two genes, slow skeletal TnT and Dnaaf3. TnI knockout mice have diaphragm weakness (1) consistent with TnT misregulation and we have observed internal organ abnormalities consistent with Dnaaf3 misregulation. Furthermore, we have confirmed the misregulation of these genes by qPCR in several non-cardiac tissues where TnI is not expressed. Excitingly, our qPCR data also shows differential gene expression in knock-in animals, which mutate only 4 nucleotides within the putative DNA regulatory region of TnI. Finally, we probed the activity of these sequences with a luciferase assay and in skeletal muscle-like cells, they enhance luciferase expression. Thus, we are proposing a novel DNA regulatory role for the cardiac troponins, independent of their protein function, that, when mutated, may cause non-cardiac disease.
References:
1. Feng, H.Z., Wei, B, Jin, J.P. Deletion of a Genomic Segment Containing the Cardiac Troponin I Gene Knocks Down Expression of the Slow Troponin T Gene and Impairs Fatigue Tolerance of Diaphragm Muscle. J Biol Chem. 284(46). (Sept. 2009)
Keywords: DNA regulation, enhancer, cardiac