Abstract
Members of the alx gene family encode transcription factors that contain a highly conserved Paired-class, DNA-binding homeodomain, and a C-terminal OAR/Aristaless domain. Phylogenetic and comparative genomic studies have revealed complex patterns of alx gene duplications during deuterostome evolution. Remarkably, alx genes have been implicated in skeletogenesis in both echinoderms and vertebrates. In this review, we provide an overview of current knowledge concerning alx genes in deuterostomes. We highlight their evolutionarily conserved role in skeletogenesis and draw parallels and distinctions between the skeletogenic gene regulatory circuitries of diverse groups within the superphylum.
Highlights
Biomineralization, the formation of mineral by living organisms, is an exceptionally widespread phenomenon and is thought to have evolved independently and rapidly in many different metazoan phyla through the deployment of a wide range of biomineralization mechanisms and chemistries
Molecular phylogenetic analysis of Alx proteins indicate that Bf-Alx1 and Bf-Alx2 form a monophyletic group, providing further support for the view that they arose from a lineage-specific gene duplication event (Figure 1; Koga et al, 2016)
Variations in the number of repeats in the coding region of alx4 are quantitatively associated with polydactyly in the Great Pyrenees dog breed (Fondon and Garner, 2004), and a 20 bp duplication in the alx4 gene is linked to congenital tibial hemimelia in Gallow cattle (Brenig et al, 2015). These findings suggest that an ancient alx gene may have constituted a conserved, core element of the ancestral vertebrate skeletogenic gene regulatory network (GRN) and that gene duplication followed by divergence of the paralogs with respect to their developmental expression and/or biochemical properties has produced multiple alx family members with overlapping functions
Summary
Members of the alx gene family encode transcription factors that contain a highly conserved Paired-class, DNA-binding homeodomain, and a C-terminal OAR/Aristaless domain. Phylogenetic and comparative genomic studies have revealed complex patterns of alx gene duplications during deuterostome evolution. Alx genes have been implicated in skeletogenesis in both echinoderms and vertebrates. We provide an overview of current knowledge concerning alx genes in deuterostomes. We highlight their evolutionarily conserved role in skeletogenesis and draw parallels and distinctions between the skeletogenic gene regulatory circuitries of diverse groups within the superphylum
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