A SoxB gene acts as an anterior gap gene and regulates posterior segment addition in a spider.

Alistair P Mcgregor,Anna Schoenauer,Christian Louis Bonatto Paese,Steven Russell,Daniel J Leite

doi:10.7554/elife.37567

Abstract

Sox genes encode a set of highly conserved transcription factors that regulate many developmental processes. In insects, the SoxB gene Dichaete is the only Sox gene known to be involved in segmentation. To determine if similar mechanisms are used in other arthropods, we investigated the role of Sox genes during segmentation in the spider Parasteatoda tepidariorum. While Dichaete does not appear to be involved in spider segmentation, we found that the closely related Sox21b-1 gene acts as a gap gene during formation of anterior segments and is also part of the segmentation clock for development of the segment addition zone and sequential addition of opisthosomal segments. Thus, we have found that two different mechanisms of segmentation in a non-mandibulate arthropod are regulated by a SoxB gene. Our work provides new insights into the function of an important and conserved gene family, and the evolution of the regulation of segmentation in arthropods.

Highlights

Arthropods are the most speciose and widespread of the animal phyla, and it is thought that their diversification and success is at least in part explained by their segmented body plan [1]
We recently described the discovery of 14 Sox genes in the genome of the spider P. tepidariorum [21] and that several of the spider Sox genes are represented by multiple copies likely produced during the whole genome duplication (WGD) in the lineage leading to this arachnid [21]
While prosomal and opisthosomal segments are generated by different mechanisms in the spider, our analysis shows that Sox21b-1 is required for segmentation in both regions of the developing spider embryo

Summary

Introduction

Arthropods are the most speciose and widespread of the animal phyla, and it is thought that their diversification and success is at least in part explained by their segmented body plan [1]. Insects utilise either derived long germ embryogenesis, where all body segments are made more or less simultaneously, or short/intermediate germ embryogenesis, where a few anterior segments are specified and posterior segments are added sequentially from a growth or segment addition zone (SAZ) [2, 3]. The segments of the posterior tagma, the opisthosoma or abdomen, are generated sequentially from a SAZ. This process is regulated by dynamic interactions between Delta-Notch and Wnt signalling to regulate caudal (cad), which in turn is required for oscillatory expression of pair-rule gene orthologues including even-skipped (eve), and runt (run) [4, 14, 15]

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