Expression of posterior Hox genes and opisthosomal appendage development in a mygalomorph spider

Abstract

Spiders represent an evolutionary successful group of chelicerate arthropods. The body of spiders is subdivided into two regions (tagmata). The anterior tagma, the prosoma, bears the head appendages and four pairs of walking legs. The segments of the posterior tagma, the opisthosoma, either lost their appendages during the course of evolution or their appendages were substantially modified to fulfill new tasks such as reproduction, gas exchange, and silk production. Previous work has shown that the homeotic Hox genes are involved in shaping the posterior appendages of spiders. In this paper, we investigate the expression of the posterior Hox genes in a tarantula that possesses some key differences of posterior appendages compared to true spiders, such as the lack of the anterior pair of spinnerets and a second set of book lungs instead of trachea. Based on the observed differences in posterior Hox gene expression in true spiders and tarantulas, we argue that subtle changes in the Hox gene expression of the Hox genes abdA and AbdB are possibly responsible for at least some of the morphological differences seen in true spiders versus tarantulas.

Evolution of the Spider Homeobox Gene Repertoire by Tandem and Whole Genome Duplication

“…Most arthropod genomes contain one Hox cluster consisting of ten ANTP-class genes ( Table 1 ), which are involved in patterning the antero-posterior axis of animals in the same relative order as the genomic organization of the genes within the cluster ( Krumlauf 2018 and the references therein). The Hox cluster is highly conserved across bilaterians, both in genomic organization and function, though differences in Hox gene expression are known to underlie changes to animal body plans ( Averof and Patel 1997 ; Abzhanov et al 1999 ; Janssen et al 2014 ; Martin et al 2016 ; Serano et al 2016 ; Janssen and Pechmann 2023 ). Hox clusters have also been retained in duplicate following WGDs, as exhibited by the four vertebrate Hox clusters that arose via the 2R WGD ( Holland and Garcia-Fernàndez 1996 ; McLysaght et al 2002 ; Holland et al 2007 ; Putnam et al 2008 ; Cañestro et al 2013 ; Holland 2013 ; Holland and Ocampo Daza 2018 ).…”

Evolution of the spider homeobox gene repertoire by tandem and whole genome duplication

“…Most arthropod genomes contain one Hox cluster consisting of ten ANTP-class genes (Table 1), which are involved in patterning the antero-posterior axis of animals in the same relative order as the genomic organisation of the genes within the cluster (Krumlauf 2018 and the references therein). The Hox cluster is highly conserved across bilaterians, both in genomic organisation and function, though differences in Hox gene expression are known to underlie changes to animal body plans (Averof and Patel 1997; Abzhanov et al 1999; Janssen et al 2014; Martin et al 2016; Serano et al 2016; Janssen and Pechmann 2023). Hox clusters have also been retained in duplicate following WGDs, as exhibited by the four vertebrate Hox clusters that arose via the 2R WGD (Holland and Garcia-Fernàndez 1996; McLysaght et al 2002; Holland et al 2007; Putnam et al 2008; Cañestro et al 2013; Holland 2013; Holland and Ocampo Daza 2018).…”