Cell types are the basic building units of multicellular life, with extensive diversities. As the number and total class of cell types change with the species evolution, it has been proposed as “evolutionary units” with the potential for quasi-independent evolutionary change. The evolution of cell types is a crucial layer of comparative cell biology but is thus far not comprehensively studied. 

The research team led by Prof. GUO Guoji from Zhejiang University School of Medicine has long been committed to research into single-cell sequencing. They have used their Microwell-seq, a high-throughput and low-cost scRNA-seq platform, to construct the first mouse cell atlas (Cell, 2018) and the first human cell atlas (Nature, 2020). Recently, GUO Guoji team worked in close cooperation with ZHANG Dan, and YUAN Guo-cheng. They defined a compendium of cell atlases using single-cell RNA-seq data from seven animal species and construct a cross-species cell-type evolutionary hierarchy. The study was published online in a research article entitled “Tracing cell-type evolution by cross-species comparison of cell atlases” on the journal of Cell Reports on March 2.

This study comprehensively characterized the conservation and divergence of cell types during age-long evolution, using  organism-wide cell atlases from seven animal species. Through systematic bioinformatics analysis, researchers proposed a cross-species organism-level cell-type evolutionary tree to trace the origin of major cell categories across evolution, and revealed important transcription factor (TF) regulons with high activity across cell categories for different species.

They found that muscle and neuron cells are conserved cell types, stromal cells and muscle cells evolved from a common ancestral cell state, and vertebrate secretory cells and neuron cells functional similarities reflect convergent evolution. In the invertebrate system, researchers have identified important evolutionary nodes. For example, important immune function cells in invertebrates, such as, gastrodermis (Nematostella), phagocytes (Schmidtea), and coelomocytes (C. elegans). In addition, the study showed a functionally conserved TF regulatory network underlying conserved cell types, and explored the characteristics of conservative TFs specific to cell type lineages.

This study reveals the conservation and diversity of cell types during species evolution, and provides a good framework for cross-platform and cross-species comparison of cell types.