Project description:During embryogenesis, cells acquire distinct fates by transitioning through transcriptional states. To uncover these transcriptional trajectories during zebrafish embryogenesis, we sequenced 38,731 cells and developed URD, a simulated diffusion-based computational reconstruction method. URD identified the trajectories of 25 cell types through early somitogenesis, gene expression along them, and their spatial origin in the blastula. Analysis of Nodal signaling mutants revealed that their transcriptomes were canalized into a subset of wild-type transcriptional trajectories. Some wild-type developmental branchpoints contained cells expressing genes characteristic of multiple fates. These cells appeared to trans-specify from one fate to another. These findings reconstruct the transcriptional trajectories of a vertebrate embryo, highlight the concurrent canalization and plasticity of embryonic specification, and provide a framework to reconstruct complex developmental trees from single-cell transcriptomes. This SuperSeries is composed of the SubSeries listed below.
Project description:Biologists rely on morphology, function, and specific markers to define the differentiation status of cells. Transcript profiling has expanded the repertoire of these markers by providing the snapshot of cellular status that reflects the activity of all genes. However, such data have been used only to assess relative similarities and differences of these cells. Here we show that principal component analysis (PCA) of global gene expression profiles map cells in multidimensional transcript profile space and the positions of differentiating cells progress in a stepwise manner along trajectories starting from undifferentiated embryonic stem (ES) cells located in the apex. We present three cell lineage trajectories, which represent the differentiation of ES cells into the first three lineages in mammalian development: primitive endoderm, trophoblast, and primitive ectoderm/neural ectoderm. The positions of the cells along these trajectories seem to reflect the developmental potency of cells and can be used as a scale for the potential of cells. Indeed, we show that embryonic germ (EG) cells and induced pluripotent (iPS) cells are mapped near the origin of the trajectories, whereas mouse embryo fibroblast (MEF) and fibroblast cell lines are mapped near the far end of the trajectories. We propose that this method can be used as the non-operational semi-quantitative definition of cell differentiation status and developmental potency. Furthermore, the global expression profiles of cell lineages provide a framework for the future study of in vitro and in vivo cell differentiation. Keywords: cell type comparison design,reference design,replicate design,time series design Most of the cells and RNA samples used in this study were described in detail previously (See paper's citation associated with this dataset). To maximize the uniformity of the microarray data, all the samples, including ones analyzed by DNA microarray previously, were hybridized to the same platform (the NIA Mouse 44K Microarray manufactured by Agilent Technologies: AMADID #015087). The intensity of each gene feature per array was extracted from scanned microarray images using Feature Extraction Software V9.5.
Project description:A hallmark of cortical evolution is the high dynamic subventricular zone (SVZ) expansion, where basal progenitors (BPs) amplify and neuronal transcriptional programs unfold. How non-coding molecular factors such as microRNAs influence these developmental trajectories and regulate the acquisition of cortical type identities is largely unknown. Here we demonstrate that miR-137 and miR-122 regulate the positioning and identity features of superficial layer cortical neurons by acting at distinct steps of their developmental trajectories. MiR-137 sustains basal progenitor amplification by reverting their neurogenic commitment and inducing high proliferative state upregulating Cd63 and inhibiting Myt1l. Cd63 is an extra-cellular matrix (ECM) receptor which interacts with b3- and 1-integrin pathways to promote proliferation, while Myt1l is a transcription factor that promotes and sustains neuronal fate. The BPs amplification by miR-137 is converted in the promotion of intracortical projecting neuron (ICPN) identity and L2/3 expansion. As opposed to miR-137, miR-122 acts postmitotically, affecting the bioelectrical properties, the calcium and cytoskeleton dynamics of newborn neurons as well as their transcriptional program, leading to a persistent molecular immaturity across time. Overall, these findings reveal that miR-137 and miR-122 are key regulators of the developmental trajectory of cortical neurons across evolution.