Inappropriate Inheritance of Histone Methylation Perturbs Muscle Structure and Function
Disciplines
Cell Biology | Developmental Biology
Abstract (300 words maximum)
The genetic makeup of living organisms can be passed down through generations via DNA. How tightly this DNA is wrapped around nucleosomes can also be inherited and affect gene expression. In eukaryotic cells, DNA is wrapped around histone proteins, which can be post-translationally modified. For example, when these histone proteins are methylated, it affects transcription of the specific genes that are associated with the histone protein. Generally, H3K4, H3K36, and H3K79 methylation are associated with active transcription, while H3K9 and H3K27 methylation are associated with repressed transcription. Histone modifying enzymes are responsible for adding and removing histone methylation marks and cooperate with one another to regulate proper gene expression during development, including establishing germline versus somatic cell fate. When these histone modifying enzymes don’t function properly, germline genes can become ectopically expressed in somatic tissues. During maternal reprogramming, SPR-5, an H3K4 demethylase, removes the active H3K4me modification, while MET-2, a methyltransferase, adds a repressive H3K9me modification. It has been shown that this maternal reprogramming is antagonized by the H3K36 methyltransferase MES-4, which maintains transcriptional memory across a subset of germline genes over generations. The maternal loss of SPR-5 and MET-2 allows for MES-4 to maintain transcriptional memory unchecked, resulting in ectopic expression germline genes in somatic tissues. The double mutants spr-5; met-2 have shown significant developmental delay and muscle defects due to this aberrant expression. Recently, we conducted motility assays on spr-5; met-2 mutants and spr-5; met-2 mutants rescued by mes-4 RNAi feeding. We observed a significant decrease in the motility of spr-5; met-2 mutants, and that motility levels returned closer to wild type levels when we knocked down mes-4. In addition, motility assays were conducted on single mutants in early generations (both spr-5 and met-2). Interestingly, spr-5 mutants showed similar motility levels to wild type while met-2 mutants showed significantly lower motility levels. These mutants were stained in order to show possible muscle myofilament defects compared to those defects seen in the double mutant stains. RNA sequencing was conducted in order to look at gene expression levels. Interestingly, there was an overall dampening in the expression levels of muscle genes needed for proper development of muscle, which rescued under mes-4 RNAi. We expect phenotypes to get worse over generations as H3K4 methylation accumulates in these mutants. These results will give us insight into how errors in maternal reprogramming can lead to tissue-specific phenotypes during development, that are also expressed in human patients.
Academic department under which the project should be listed
CSM - Molecular and Cellular Biology
Primary Investigator (PI) Name
Brandon Carpenter
Inappropriate Inheritance of Histone Methylation Perturbs Muscle Structure and Function
The genetic makeup of living organisms can be passed down through generations via DNA. How tightly this DNA is wrapped around nucleosomes can also be inherited and affect gene expression. In eukaryotic cells, DNA is wrapped around histone proteins, which can be post-translationally modified. For example, when these histone proteins are methylated, it affects transcription of the specific genes that are associated with the histone protein. Generally, H3K4, H3K36, and H3K79 methylation are associated with active transcription, while H3K9 and H3K27 methylation are associated with repressed transcription. Histone modifying enzymes are responsible for adding and removing histone methylation marks and cooperate with one another to regulate proper gene expression during development, including establishing germline versus somatic cell fate. When these histone modifying enzymes don’t function properly, germline genes can become ectopically expressed in somatic tissues. During maternal reprogramming, SPR-5, an H3K4 demethylase, removes the active H3K4me modification, while MET-2, a methyltransferase, adds a repressive H3K9me modification. It has been shown that this maternal reprogramming is antagonized by the H3K36 methyltransferase MES-4, which maintains transcriptional memory across a subset of germline genes over generations. The maternal loss of SPR-5 and MET-2 allows for MES-4 to maintain transcriptional memory unchecked, resulting in ectopic expression germline genes in somatic tissues. The double mutants spr-5; met-2 have shown significant developmental delay and muscle defects due to this aberrant expression. Recently, we conducted motility assays on spr-5; met-2 mutants and spr-5; met-2 mutants rescued by mes-4 RNAi feeding. We observed a significant decrease in the motility of spr-5; met-2 mutants, and that motility levels returned closer to wild type levels when we knocked down mes-4. In addition, motility assays were conducted on single mutants in early generations (both spr-5 and met-2). Interestingly, spr-5 mutants showed similar motility levels to wild type while met-2 mutants showed significantly lower motility levels. These mutants were stained in order to show possible muscle myofilament defects compared to those defects seen in the double mutant stains. RNA sequencing was conducted in order to look at gene expression levels. Interestingly, there was an overall dampening in the expression levels of muscle genes needed for proper development of muscle, which rescued under mes-4 RNAi. We expect phenotypes to get worse over generations as H3K4 methylation accumulates in these mutants. These results will give us insight into how errors in maternal reprogramming can lead to tissue-specific phenotypes during development, that are also expressed in human patients.