Nuclear Envelope Directed Genome Organization in Myogenesis and Emery-Dreifuss Muscular Dystrophy

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Each individual's genome is identical in all the cells of their bodies. Yet these cells are able to achieve incredibly different forms from those making the heart to the liver or brain. There are many aspects of genome regulation that enable different subsets of the genes in the genome to be expressed to help each tissue develop. One of the least understood of these is how the position of a gene in the nucleus contributes to its regulation. Many genes important for tissue development move from the edge of the nucleus to the interior concomitant with their being expressed. Other genes that are antagonistic to tissue development move to the edge of the nucleus and get shut down. In general the genes located at nuclear periphery tend to be shut down and there is evidence that disruption of nuclear spatial genome organisation underlies some developmental defects and diseases. We have previously identified proteins located at the edge of the nucleus that are important for establishing spatial genome organisation. Some of these proteins were found only in liver and affected genome organisation in liver, while others were found only in fat and affected genome organisation in fat and yet others were found only in muscle and affected genome organisation in muscle. We found five such proteins in muscle and different ones affected distinct subsets of genes important for muscle development. In separate work we were studying the muscle-wasting disease Emery-Dreifuss muscular dystrophy. Mutations in seven different proteins have been found to cause this disease, but a little over half of clinically diagnosed Emery-Dreifuss patients do not have mutations in these seven proteins and so must have other causes. We analysed 62 such Emery-Dreifuss patients and found that 11 of them have mutations in four of the five genome-organising muscle proteins. The goal of the proposed project is to test whether the mutations found can explain the pathology of the disease by engineering the mutations into a cell system where muscle development can be followed in a dish and also into mice. The former can give information about when and where specific defects occur in individual muscle cells while the latter can give information about systemic muscle function, metabolism and pathology. Levels of muscle metabolic markers will be assayed as well as markers of other tissues in case the mutant genome-organising proteins fail to shut down genes from other tissues as this could help explain Emery-Dreifuss muscle defects. Muscle size, muscle regeneration and muscle stem cell function will also be assayed. To ascertain whether genome organisation defects can explain the cell and tissue pathology, the expression of different genes and other genome regulatory elements will be determined by genome-wide sequencing approaches and the position of genes in normal versus mutant cells and tissues observed using microscopy. The above studies will be done both using mutants in the genome-organising proteins and in other proteins that cause Emery-Dreifuss muscular dystrophy to determine if the underlying defects match. Finally, we will investigate the mechanism behind the genome organisation changes by making specific modifications to the genome around the affected genes and determining whether these modifications block the normal gene movements to or from the nuclear edge. This study should both provide insights into the fundamental mechanisms underlying genome organisation and also identify the gene and metabolic pathways altered in Emery-Dreifuss muscular dystrophy. This combined understanding could lead to therapeutic approaches focused on restoring the proper metabolic balance by supplying missing metabolites and enzymes.