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An axial Hox code controls tissue segmentation and body patterning in Nematostella vectensis

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Science  28 Sep 2018:
Vol. 361, Issue 6409, pp. 1377-1380
DOI: 10.1126/science.aar8384

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Hox code in segmentation and patterning

Hox genes encode conserved transcription factors that are best known for their role in governing anterior-posterior body patterning in diverse bilaterian animals. He et al. used a combination of CRISPR mutagenesis and short hairpin RNA–based gene knockdowns to interrogate Hox gene function in a cnidarian, the sea anemone Nematostella vectensis (see the Perspective by Arendt). Four homeobox-containing genes constitute a molecular network that coordinately controls the morphogenesis of radial endodermal segments and the patterning of tentacles. Thus, an ancient Hox code may have evolved to regulate both tissue segmentation and body patterning in the bilaterian-cnidarian common ancestor.

Science, this issue p. 1377; see also p. 1310

Abstract

Hox genes encode conserved developmental transcription factors that govern anterior-posterior (A-P) pattering in diverse bilaterian animals, which display bilateral symmetry. Although Hox genes are also present within Cnidaria, these simple animals lack a definitive A-P axis, leaving it unclear how and when a functionally integrated Hox code arose during evolution. We used short hairpin RNA (shRNA)–mediated knockdown and CRISPR-Cas9 mutagenesis to demonstrate that a Hox-Gbx network controls radial segmentation of the larval endoderm during development of the sea anemone Nematostella vectensis. Loss of Hox-Gbx activity also elicits marked defects in tentacle patterning along the directive (orthogonal) axis of primary polyps. On the basis of our results, we propose that an axial Hox code may have controlled body patterning and tissue segmentation before the evolution of the bilaterian A-P axis.

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