Developmental single-cell transcriptomics in the Lytechinus variegatus sea urchin embryo.


Using scRNA-seq coupled with computational approaches, we studied transcriptional changes in cell states of sea urchin embryos during development to the larval stage. Eighteen closely spaced time points were taken during the first 24 hours of development of Lytechinus variegatus (Lv). Developmental trajectories were constructed using Waddington-OT, a computational approach to "stitch" together developmental timepoints. Skeletogenic and primordial germ cell trajectories diverged early in cleavage. Ectodermal progenitors were distinct from other lineages by sixth cleavage, though a small percentage of ectoderm cells briefly co-expressed endoderm markers indicating an early ecto-endoderm cell state, likely in cells originating from the equatorial region of the egg. Endomesoderm cells originated at 6th cleavage also and this state persisted for more than two cleavages, then diverged into distinct endoderm and mesoderm fates asynchronously, with some cells retaining an intermediate specification status until gastrulation. 79 of 80 genes (99%) examined, and included in published developmental gene regulatory networks (dGRNs), are present in the Lv-scRNA-seq dataset, and expressed in the correct lineages in which the dGRN circuits operate.





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Massri, Abdull J, Laura Greenstreet, Anton Afanassiev, Alejandro Berrio, Gregory A Wray, Geoffrey Schiebinger and David R McClay (2021). Developmental single-cell transcriptomics in the Lytechinus variegatus sea urchin embryo. Development (Cambridge, England). 10.1242/dev.198614 Retrieved from

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Gregory Allan Wray

Professor of Biology

I study the evolution of genes and genomes with the broad aim of understanding the origins of biological diversity. My approach focuses on changes in the expression of genes using both empirical and computational approaches and spans scales of biological organization from single nucleotides through gene networks to entire genomes. At the finer end of this spectrum of scale, I am focusing on understanding the functional consequences and fitness components of specific genetic variants within regulatory sequences of several genes associated with ecologically relevant traits. At the other end of the scale, I am developing molecular and analytical methods to detect changes in gene function throughout entire genomes, including statistical frameworks for detecting natural selection on regulatory elements and empirical approaches to identify functional variation in transcriptional regulation. At intermediate scales, I am investigating functional variation within a dense gene network in the context of wild populations and natural perturbations. My research leverages the advantages of several different model systems, but primarily focuses on sea urchins and primates (including humans).


David R. McClay

Arthur S. Pearse Distinguished Professor of Biology

We ask how the embryo works. Prior to morphogenesis the embryo specifies each cell through transcriptional regulation and signaling. Our research builds gene regulatory networks to understand how that early specification works. We then ask how this specification programs cells for their morphogenetic movements at gastrulation, and how the cells deploy patterning information.
Current projects examine 1) novel signal transduction mechanisms that establish and maintain embryonic boundaries
mold the embryo at gastrulation; 2) specification of primary mesenchyme cells in such a way that they are prepared to execute an epithelial-mesenchymal transition, and then study mechanistically the regulation of that transition; 3) the specification of endoderm necessary for invagination of the archenteron; 4) formation of the oral/aboral ectoderm and the means by which patterning information is distributed three dimensionally around the embryo. That information is necessary for patterning and inducing skeletogenesis.
Other projects examine neural tube folding with the goal of identifying genes associated with neural tube defects. Finally, a large current effort in systems biology is being expended with the goal of enlarging our knowledge of early networks and how they interact.

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