Single-cell RNA sequencing provides novel insights into spider development and represents an innovative alternative to study the evolution and development of panarthropods

Abstract: Panarthropoda is a monophyletic group of invertebrate animals with a segmented body, paired appendages, dorsal brain, and ventral nerve cords. In order to study the mechanisms underpining their evolution, I study the genetic factors that drive their development. A typical research strategy is the candidate gene approach, in which orthologs of genes from a well established model organisms such as the fruit fly Drosophila melanogaster are studied in other more or less related species for comparison.Recently developed single-cell RNA sequencing technologies allow the profiling of gene expression on the level of individual cells, and thus provide a much more detailed insight into gene expression.In Paper-I, I applied the candidate gene approach to study the potential role of two transcription factors, called tiptop/teashirt and spalt, as trunk-selectors in panarthropods.In Paper-II, I applied single-cell RNA sequencing to obtain the transcriptome of embryonic cells from spiders at mid-to-late stage in development. This generated a gene expression/gene-cell matrix that I analyzed to define the identity of cell clusters.In Paper-III, I present an improved SCS data analysis based on the data presented in Paper-II. This revealed a number of new cell clusters including a cluster that is characterized by known eye-developmental genes, genes that have previously not been identified as eye-developmental genes, and hitherto un-investigated genes. My in-situ hybridization analyis shows that these genes are potential novel factors of eye development in the spider.This work constitutes a successful example of the advantages of applying scRNA-seq in the study of panarthropod evolution and development.