Periodic Reporting for period 3 - SafeFate (Safeguarding Cell Fate by Terminal Repression during Development and Disease)
Période du rapport: 2022-02-01 au 2023-07-31
Molecular master regulators and transcription factors that activate gene networks during development are well characterized. Whereas the mechanisms that terminally repress alternative cell fates to determine cell identity and function remain only partially understood. This project aims to demonstrate that active gene silencing, so called terminal repression, is a universal new mechanism important to induce and maintain cell identity. Our recent work showed that the neuron-specific transcription repressor Myt1l is essential for neuronal cell identity, as it represses non-neuronal programs in neurons. The research in this project investigates if there are additional terminal repressors that prevent alternative lineages from developing and if failure to repress unwanted cell fate programs upon mutation of these factors, could result in disease. Our project will have an impact for society, because we will investigate new directions how to fight diseases associated with loss of cell identity and we will develop new protocols to reprogram cells for regenerative medicine. Our general concept can be extended to various other cell types for which new reprogramming protocols will enable to generate in vitro counterparts for disease modeling or regenerative medicine.
We have already made significant progress towards our research goals for each of the three aims. For aim one that investigates if depletion of Myt1l can cause loss of neuronal cell identity and mental disorders we have focused on studying our new Myt1l knockout mouse model. We found striking neurological phenotypes that resemble MYT1L syndrome patients. In addition, we have started to investigate loss of function associated phenotypes in human induced neurons. We will continue to investigate whether the phenotypes are conserved between mice and man and if Myt1l mutation alone can indeed cause autism-associated disorders observed in patients. The second aim will determine the mechanistic link between MYT1L and the epigenetic machinery to continuously silence unwanted cell identities. To that end we have recently established immunoprecipitation followed by mass spectrometric approaches to identify such interactors. Strikingly, we found MYT1L to interact with many ASD-associated chromatin regulators, which suggests that they could function as protein complexes to allow normal neuronal development and function and prevent disorders such as ASD. The next step will be to confirm these interactions and study their functional relevance. Aim three will identify terminal repressors in other cell types. We have already bioinformatically identified terminal repressor candidates in non-neuronal cell types. Upon testing the top candidates in reprogramming experiments we will study the cell fate inducing mechanism of these terminal repressor candidates using functional genomics and protein engineering studies. Along the lines of this aim, we have published our findings that not only cell fate conversion to neurons (ectoderm), but also to muscle cells (mesoderm) is hampered by pioneer factor promiscuity, which suggests that also in other lineages safeguarding mechanisms such as terminal repression could exist to enable faithful cell fate induction in a high impact journal (Lee, Mall et al. Nature Cell Biol., 2020).
Within this project we have identified unexpected phenotypes upon MYT1L deficiency in mouse and human neurons on the neuronal network level. This effect is amenable to acute pharmacological manipulation in postmitotic neurons and FDA-approved drugs can even normalize behavior defects in mutant mice. This shows that MYT1L mutation does not only alter neurodevelopment, as was assumed in the field, but results in druggable electrophysiological defects in vitro and behavior phenotypes in vivo that can be treated by drugs even after development is complete. This suggests that patients suffering from terminal repressor loss could benefit from targeted treatments even at later stages of development (coinciding with diagnosis later in life), which could be a significant advancement and could enable specific treatments for such disorders. This we believe could lead to ground breaking personalized strategies and treatment options for this neurodevelopmental disease that could be generalized to other organ systems in the future.