Periodic Reporting for period 4 - REPROWORM (Safeguarding Cell Identities: Mechanisms Counteracting Cell Fate Reprogramming)
Berichtszeitraum: 2019-09-01 bis 2021-02-28
In order to enhance the identification of reprogramming barriers we set up a novel high-throughput genetic screening system and identified additional genetic factors that inhibit reprogramming of cell fates. This system allowed the identification of the chromatin-regulating factor MRG-1 (MRG15 in humans) as a barrier for cellular reprogramming in C. elegans (Hajduskova et al., 2019 Genetics). Biochemical characterization revealed that MRG-1 interacts with the methyltransferase SET-26 in order to safeguard germ cells (Hajduskova et al., 2019 Genetics). Besides chromatin factors, metabolome regulators such as dehydrogenases were also identified as reprogramming barriers, which will be further characterized with respect to molecular mechanisms and conservation in mammals. The histone chaperones LIN-53 (CAF-1p48/RBBP4) and the chromatin remodeler FACT exemplify the high level of functional conservation from nematodes to human for reprogramming barriers. By continuing to study our first identified reprogramming barrier LIN-53, we revealed an unexpected antagonistic relationship of the conserved NOTCH signaling system with the repressive chromatin regulator PRC2. Increased activity of the Notch signaling pathway counteracts PRC2-mediated chromatin repression, thereby enhancing the reprogramming of germ cells into neurons (Seelk et al., 2016 Elife).
Furthermore, we revealed that LIN-53 is required for normal lifespan and muscle homeostasis in C. elegans. We could show that LIN-53 regulates metabolism and the levels of the sugar Trehalose, which is essential for normal lifespan. While metabolism regulation by LIN-53 occurs via the histone-deacetlyase complex SIN3, LIN-53 maintains muscle integrity during aging via the chromatin-remodeling complex NuRD (Müthel et al., 2019 Aging Cell). Strikingly, there is evidence that the human counterpart of LIN-53, CAF-1p48/RBBP4, has a conserved role in regulating lifespan and preventing myopathy in humans. We discovered that expression and localization of the human homolog CAF-1p48/RBBP4 is impaired in primary myoblasts of human myopathy patients. By introducing the respective mutations of the patients we have now established C. elegans as a genetic disease model to systematically investigate the impact of impaired chromatin regulation on muscular homeostasis in myopathy patients.
We are continuing to reveal the mechanisms that safeguard cell fates and maintain tissue identities in C. elegans. The overall 60% homology of the genome between C. elegans and humans may lead to the identification of highly conserved mechanisms that act as barriers to cellular reprogramming and play important roles during lifespan and tissue homeostasis. Until the end of REPROWORM, the characterization of additional unexpected reprogramming barriers, such as genes encoding for mitochondrial proteins, will reveal unique insights into how cell identities are protected by linking distinct biological processes including epigenetics and metabolomics in an intact organism.