Expression and function of a starfish Otx ortholog, AmOtx: a conserved role for Otx proteins in endoderm development that predates divergence of the eleutherozoa

Abstract

The sea urchin orthodenticle (Otx)-related transcription factor is an early activator of other endomesodermally expressed transcription factors. Its normal function is required for the development of the archenteron and to lock cells into endomesodermal fate. To determine if this is a basal Otx function in echinoderms we have studied the role of an Otx ortholog in a starfish, Asterina miniata. The patterns of AmOtx expression are found to be similar, in many details, to those reported for other indirectly developing echinoderms and hemichordates, suggestive of a conserved function both in endoderm development and ciliary band formation in these two phyla. When downstream targets of the AmOtx protein are suppressed using a dominant engrailed repressor strategy, embryos fail to develop the endodermal component of the archenteron, though initial phases of mesoderm development proceed normally. The function of Otx proteins in endodermal development at least predated the evolution of the free-living echinoderms (Eleutherozoa).

Gene expression profiling of genetically determined growth variation in bivalve larvae (Crassostrea gigas)

“…For example, during fruit fly development many genes are expressed at peak levels for a brief developmental period, while others increase gradually to a stable maximum (Arbeitman et al, 2002). Similarly complex patterns of differential gene expression have been observed during development of other species of marine invertebrates (Char et al, 1993;Marsh et al, 2000;Hinman et al, 2003). Differences in gene expression at a particular developmental stage might reflect differences in the timing of a developmental peak in expression, or differences in the overall level of expression throughout development.…”

Gene expression profiling during the embryo‐to‐larva transition in the giant red sea urchin Mesocentrotus franciscanus

“…The embryogenesis and early larval development of echinoderms involve the interactions of regulatory, structural, and functional genes that, in some cases, are highly conserved even among distantly related echinoderm species (Hinman & Davidson, 2003a,b; Hinman, Nguyen, Cameron, et al., 2003; Hinman, Nguyen, & Davidson, 2003). However, differences in skeleton formation and embryonic territories specification in this group are the result of evolutionary changes, which include gene duplications, protein function diversification, and genes co‐opted to different functions (Dylus et al., 2016; Hinman & Davidson, 2007; Hinman, Nguyen, Cameron, et al., 2003; McCauley et al., 2010, 2012).…”

“…In echinoderms, for example, the unique combination of regulatory genes (e.g., transcription factors) in embryonic space and time contribute to shaping the regulatory program for larval skeletogenesis (Dylus et al., 2016; Gao & Davidson, 2008), endomesodermal (Peter & Davidson, 2010), and ectodermal specification (Nakata & Minokawa, 2009). Despite the differences in larval development in this group (e.g., pluteus‐, bipinnaria‐, and auricularia‐like larvae), comparisons of their GRN architectures have detected highly conserved orthologous regulatory genes among the extant echinoderm classes (Hinman & Davidson, 2003a,b; Hinman, Nguyen, Cameron, & Davidson, 2003; Hinman, Nguyen, & Davidson, 2003). While the network logic employed is the same in these organisms, the transcription factors underlying certain functions have been the subject of evolutionary change, resulting in gene duplications, protein function diversification, and regulatory genes co‐opted to different functions (Dylus et al., 2016; Hinman & Davidson, 2007; Hinman, Nguyen, Cameron, et al., 2003; McCauley, Weideman, & Hinman, 2010; McCauley, Wright, Exner, Kitazawa, & Hinman, 2012).…”

Making very similar embryos with divergent genomes: conservation of regulatory mechanisms ofOtxbetween the ascidiansHalocynthia roretziandCiona intestinalis

“…The authors thus proposed that the regulatory logic of Brachyury may differ in Halocynthia and Ciona. Comparison between two distantly related echinoderm, the starfish A. miniata and the sea urchin S. purpuratus, revealed that although some gene regulatory networks have persisted unaltered since the Cambrian period, others have extensively diverged (Hinman et al, 2003). The comparative analysis of the Brachyury and Otx regulatory logics between ascidians suggests that a similar phenomenon may also have occurred in this phylum.…”