Every year about 7.9 million infants are born with serious birth defects, including craniofacial, intellectual disabilities, organs malformation and developmental delays. More importantly birth defects are the leading cause of child mortality in United States. Recently, many children with birth defects were identified as having mutations in histone modifying enzymes. These include Kabuki Syndrome patients and 3 children with mutations in the histone demethylase LSD1/KDM1. These children all have neurodevelopmental disorders. It is thought that the failure to properly regulate histone methylation in these patients leads to inappropriate transcription. However, it is unclear to what extent inappropriate transcription is heritable within developing embryos. It is also unclear how inappropriate transcription leads to defects. We have recently developed a C. elegans model of inappropriately inherited histone methylation due to failure in epigenetic reprogramming at fertilization. In C. elegans, two epigenetic enzymes, the H3K4me2 demethylase, SPR-5 (ortholog of LSD1), and the H3K9 methyltransferase, MET-2 (ortholog of SetDB1), are maternally deposited into the oocyte. These chromatin modifiers cooperate to reestablish the epigenetic ground state by modifying histone methylation. Progeny of worms lacking SPR-5 and MET-2 accumulate high levels of H3K4me2, resulting in complete sterility and developmental delay, caused by the improper maintenance of germline expression in the soma. Importantly, the C. elegans embryonic lineage is completely invariant. As a result, spr-5;met-2 mutants provide a unique opportunity to understand the rules governing how inappropriate histone methylation affects transcription and cell fate at the single cell level. To do this, I will use confocal imaging to perform automated lineage tracing. This will enable me to detect defects in the timing of cell division, the number of cell divisions, and the survival/death of individual cells in every embryonic lineage. I will combine this with single cell RNA- seq analysis to determine cell by cell, which somatic cells inappropriate express germline genes. By comparing the lineage defects to the inappropriate expression of germline genes in every cell, I will learn the rules governing how inappropriate histone methylation affects transcription and cell fate in developing tissues. Thus, successful completion of this grant will provide a framework for understanding childhood diseases, such as Kabuki Syndrome, caused by mutations in histone modifying enzymes.
Recently it was found that a number of childhood disorders are caused by mutations in enzymes that modify the packaging of DNA. However, it is unclear how transcriptional changes resulting from these mutations are inherited from cell to cell and cause defects. By examining a worm model of inherited defects in the packaging of DNA at the single cell level, I will learn the rules governing how these types of mutations affect the development of tissues.
