An atlas of spider development at single-cell resolution provides new insights into arthropod embryogenesis

Abstract

AbstractSpiders are a diverse order of chelicerates that diverged from other arthropods over 500 million years ago. Research on spider embryogenesis has made important contributions to understanding the evolution of animal development. In particular, studies of the common house spider Parasteatoda tepidariorum using developmental candidate gene approaches have provided key insights into the regulation and evolution of many processes including axis formation, segmentation and patterning. However, there remains a paucity of knowledge about the cells that build spider embryos, their gene expression profiles and fate. Single-cell transcriptomic analyses have been revolutionary in describing these complex landscapes of cellular genetics in a range of animals. Therefore, we carried out single-cell RNA sequencing of P. tepidariorum embryos at stages 7, 8 and 9, which encompass the establishment and patterning of the body plan, and initial differentiation of many tissues and organs. We identified 23 cell clusters marked by many developmental toolkit genes, as well as a plethora of non-candidate genes not previously investigated. We found many Hox genes were markers of cell clusters, and Hox gene paralogs often were present in different clusters. This provided further evidence of sub- and/or neo-functionalisation of these important developmental genes after the whole genome duplication in the arachnopulmonate ancestor. We also examined the spatial expression of marker genes for each cluster to generate a comprehensive cell atlas of these embryonic stages. This revealed new insights into the cellular basis and genetic regulation of head patterning, hematopoiesis, limb development, gut development and posterior segmentation. This atlas will serve as a platform for future analysis of spider cell specification and fate, and the evolution of these processes among animals at cellular resolution.