Single‐cell sequencing reveals potential novel insights into appendage‐patterning and joint‐development in a spider

Background Jointed appendages represent one of the key innovations of arthropods, and thus understanding the development and evolution of these structures is important for the understanding of the evolutionary success of Arthropoda. In this paper, we analyze a cell cluster that was identified in a previous single‐cell sequencing (SCS) experiment on embryos of the spider Parasteatoda tepidariorum . This cell cluster is characterized by marker genes that suggest a role in appendage patterning and joint development. Results We analyzed the expression profiles of these marker genes showing that they are expressed in the developing appendages and in a pattern that suggests a potential function during joint development. Several of the investigated genes represent new and unexpected factors such as dysfusion ( dysf ), spätzle3 ( spz3 ), seven‐up ( svp ). In order to study their evolutionary origin, we also investigated orthologs of the identified appendage‐patterning genes in the harvestman Phalangium opilio , a distantly related chelicerate. Conclusion Our work highlights the usefulness of SCS experiments for the identification of potential new genetic factors that are involved in specific developmental processes. The current data provide potential new insights into the gene regulatory networks that underlie arthropod joint development.