Ectopic transcription due to inappropriately inherited histone methylation may interfere with the ongoing function of terminally differentiated cells Open Access
Rodriguez, Juan D (Summer 2023)
Published
Abstract
Many human neurodevelopmental disorders are caused by de novo mutations in histone modifying enzymes. These patients have craniofacial defects, developmental delay, intellectual disability and behavioral abnormalities, but it remains unclear how the mutations lead to such developmental defects. Here we take advantage of the invariant C. elegans lineage, along with a unique double mutant in the H3K4me1/2 demethylase SPR-5/LSD1/KDM1A, and the H3K9 methyltransferase MET-2/SETDB1 to address this question. We demonstrate that spr-5; met-2 double mutant worms have a severe chemotaxis defect that is dependent upon the ectopic expression of germline genes in somatic tissues. In addition, by performing single-cell RNAseq, we find that germline genes begin to be ectopically expression widely in spr-5; met-2 embryos. However, surprisingly we found that spr-5; met-2 mutants have no somatic lineage defects p to the 200-cell stage of embryogenesis. This suggests that the altered chemotaxis behavior may be due to ongoing defects in terminally differentiated cells rather than a defect in development. To test this directly, we used RNAi to shut off the ectopic expression of germline genes in L2 spr-5; met-2 larvae, which have a fully formed nervous system. Remarkably, we find that shutting off the ectopic germline expression rescues normal chemotaxis behavior in the same adult worms that previously had a chemotaxis defect at the L2 stage. This suggests that ongoing ectopic transcription can block normal behavior in a fully intact nervous system. These data raise the possibility that intellectual disability and altered behavior in neurodevelopmental syndromes, caused by mutations in histone modifying enzymes, could be due to ongoing ectopic transcription and may be reversible.
Table of Contents
Table of Contents
Chapter 1. Introduction and Background.. 1
Histone modifcation. 2
Histone phosporylation
Histone methylation
Histone acetylation
Histone ubiquitination
2 Chromatin………………………………………………………………………………………………………4
Chromatin remodeling complexes
Chromatin as an epigenetic regulation during development
Histone methylation trancriptional memory
Suppressor of presenilin (SPR) rescue of the egg laying phenotype
The methyltransferase MET-2 is a regulator of vulval cell specification
Table of chromatin enzymes
References……………………………………………………………………………………………………...12
Chapter 2. Materials AND METHODS A practical guide for using lineage tracing and single cell RNA-seq in C. elegans to analyze transgenerational epigenetic phenotypes inherited from germ cells……………………………………………………………14
Abstract. 16
Introduction. 17
Materials................................................................ 19
Methods………………………………………………………………………………………………………….22
Figures and Figures Legends……………………………………………………………………………….. 38
References. 45
Chapter 3. C. elegans establishes germline versus soma by balancing inherited histone methylation. 46
Abstract. 48
Introduction. 49
Resrults. 53
Discussion. 64
Materials and Methods. 73
Acknowledgements. 82
References. 83
Figures and Figures Legends. 89
Chapter 4. Ectopic transcription due to inappropriately inherited histone methylation may interfere with the ongoing function of terminally differentiated cells. 97
Abstract................................................................. 98
Introduction. 99
Results. 104
Discussion. 111
Materials and Methods……………………………………………………………………………………...116
Acknowledgements ……………................................................................................................................................. 120
References........................................................... 121
Figures and Figure Legends. 123
Chapter 5. dISCUSSION. 130
Epigenetic reprograming at fertilization by SPR-5 and MET-2 is required to prevent embryonic and larvae phenotypes
spr-5; met-2 have a germline lineage defect
Proposed mechanism
Conclusion
Appendix A. A model for Epigenetic Inhibition via Transvection in the Mouse. 140
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