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PRC2-mediated repression is essential to maintain identity and function of differentiated dopaminergic and serotonergic neurons [snRNA-Seq]

ABSTRACT: Neurons of the CNS must maintain their distinct identity over an entire lifespan. Apart from instructive information provided by transcription factors driving neuron specific genes, other gene programs need to be permanently silenced. The mechanisms governing enduring gene-silencing in neurons are largely unknown, as are the consequences if they fail. Here we show that loss of the Polycomb repressive complex 2 (PRC2) obligate unit Eed in differentiated murine midbrain dopamine (mDA) neurons resulted in progressive loss of the H3K27me3 histone modification followed by upregulation of PRC2 targets, also highly enriched for the constitutive heterochromatin H3K9me3 modification. This was followed by reduced expression of mDA neuron-identity genes, particularly evident in the Substantia nigra pars compacta. Consequently, mDA-neuronal function was severely disrupted, causing parkinsonian-like motor skill deficits. Deletion of Eed in differentiated serotonergic (5HT) neurons resulted in a similar upregulation of PRC2-targets and reduced expression of genes defining 5HT neurons, which promoted loss of serotonergic identity followed by loss of function and altered behaviour. Overall, our results reveal that PRC2 inactivation leads to a selective and progressive loss of mDA or 5HT neuronal identity and function, but not to any loss of cells. Thus, our study shows that PRC2-dependent maintenance of neuronal identity is essential and safeguards against expression of other non-relevant gene programs and loss of neuronal function.

ORGANISM(S): Mus musculus

PROVIDER: GSE189329 | GEO | 2022/07/11

REPOSITORIES: GEO

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Project description:Mutations in the SNCA gene cause autosomal dominant Parkinson’s disease (PD), with progressive loss of dopaminergic neurons in the substantia nigra, and accumulation of aggregates of α-synuclein. However, the sequence of molecular events that proceed from the SNCA mutation during development, to its end stage pathology is unknown. Utilising human induced pluripotent stem cells (hiPSCs) with SNCA mutations, we resolved the temporal sequence of pathophysiological events that occur during neuronal differentiation in order to discover the early, and likely causative, events in synucleinopathies. We adapted a small molecule-based protocol that generates highly enriched midbrain dopaminergic (mDA) neurons (>80%). We characterised their molecular identity using single-cell RNA sequencing and their functional identity through the synthesis and secretion of dopamine, the ability to generate action potentials, and form functional synapses and networks. RNA velocity analyses confirmed the developmental transcriptomic trajectory of midbrain neural precursors into different mDA neuronal clusters. To characterise the synucleinopathy, we adopted super-resolution methods to determine the number, size, and structure of aggregates in SNCA-mutant mDA neurons. By day 27 of differentiation, prior to maturation to mDA neurons of molecular and functional identity, we demonstrate the formation of small aggregates; specifically, β-sheet rich oligomeric aggregates, in SNCA-mutant midbrain immature neurons. The aggregation progresses over time to accumulate phosphorylated and fibrillar aggregates. When the midbrain neurons were functional, we observed impaired intracellular calcium signalling, evidenced with an increased basal calcium level and impairments in both cytosolic and mitochondrial calcium rearrangements. Once midbrain identity fully developed, SNCA-mutant neurons exhibited mitochondrial dysfunction, oxidative stress, lysosomal swelling as well as an upregulation of mitophagy and autophagy. In addition, SNCA-mutant neurons displayed pathophysiological excitability, revealed as a depolarised resting membrane potential, an increased input resistance, and impaired firing properties. Ultimately these multiple cellular stresses lead to an increase in cell death by day 62 post-differentiation. Our differentiation paradigm generates an efficient model for studying disease mechanisms in PD, and highlights that protein misfolding to generate intraneuronal oligomers is one of the earliest critical events driving disease in human neurons, rather than a late-stage hallmark of the disease.

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PRC2-mediated repression is essential to maintain identity and function of differentiated dopaminergic and serotonergic neurons [snRNA-Seq]

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