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

Abstract

Spiders 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.

Coming into clear sight at last: Ancestral and derived events during chelicerate visual system development

“…[ 23,24 ] One of these studies, however, suspected earlier Pax6 expression in the ocular segment of C. salei , in part based on preliminary expression evidence. [ 24 ] It is thus not wholly unexpected that a recently conducted single‐cell transcriptome study finally documented the prominent expression of both ey and toy in the early ocular segment of P. tepidariorum (Figure 2A), [ 31 ] filling an important knowledge gap.…”

“…[ 39,41,42 ] The newly available detailed description of Six3 homolog expression in the early P. tepidariorum germband reveals that one of the two paralogs ( Pt‐Six3.1 ) is initially expressed in a slim stripe anterior of the ey and toy ocular segment expression domain (Figure 2B). [ 31 ] While this anterior expression of Pt‐Six3.1 may initially transiently overlap with ey and toy [ 31 ] (Figures 3 and S4), this earliest Pt‐Six3.1 expression domain is strikingly similar to the earliest expression of Six3 in the blastoderm embryo of Tribolium . [ 36 ]…”

High sensitivity single cell RNA sequencing with split pool barcoding

“…Contrary to other approaches, combinatorial barcoding does not require any complex microfluidics or other specialized equipment. Over the past few years, this approach has been widely adopted to study developmental processes and disease progression at scale [13][14][15][16][17][18][19][20][21][22][23][24][25][26] .…”

Extraembryonic tissue in chelicerates: a review and outlook

“…[83]; Leite et al . [84]). First analyses of cell clusters and the genes expressed therein led to the suggestion that the cells of the dorsal field are indeed not extraembryonic but might contribute to the formation of hemocytes and other cell types [83].…”

“…By using single-cell RNA sequencing, recent studies independently identified genes that are expressed in the dorsal field (e.g. noggin, see figure 1i; Akiyama-Oda et al [83]; Leite et al [84]). First analyses of cell clusters and the genes expressed therein led to the suggestion that the cells of the dorsal field are indeed not extraembryonic but might contribute to the formation of hemocytes and other cell types [83].…”