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Resolving transcriptional states and predicting lineages in the annelid Capitella teleta using single-cell RNAseq

ABSTRACT: Here we use a whole-organism, single-cell transcriptomic approach to map larval cell types in the annelid Capitella teleta at 24- and 48-hours post gastrulation (stages 4 and 5). We identified eight unique cell clusters (undifferentiated precursors, ectoderm, muscle, ciliary-band, gut, neurons, neurosecretory cells and protonephridia), thus helping to identify previously uncharacterized molecular signatures such as novel myogenic and neurosecretory cell markers. Analysis of coregulatory programs in individual clusters revealed gene interactions that can be used for comparisons of cell types across taxa. We examined the neural and neurosecretory clusters more deeply and characterized a differentiation trajectory starting from dividing precursors to neurons using Monocle3 and velocyto. Pseudotime analysis along this trajectory identified temporally-distinct cell states undergoing progressive gene expression changes over time. Our data revealed two potentially distinct neural differentiation trajectories including an early trajectory for brain neurosecretory cells. This work provides a valuable resource for future functional investigations to better understanding neurogenesis and the transitions from neural precursors to neurons in an annelid.

ORGANISM(S): Capitella teleta

PROVIDER: GSE159564 | GEO | 2020/10/20

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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Resolving transcriptional states and predicting lineages in the annelid Capitella teleta using single-cell RNAseq

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