Hox genes code body plan in sea anemones


Researchers from the Stowers Institute for Medical Research have found that Hox genes significantly control the radially symmetric body plan of the starlet sea anemone, Nematostella vectensis. According to the research the sea anemone offers us a window into the probable, ancient past of Hox gene function.

Hox genes are key regulators of the way the bodies of bilaterally symmetrical animals form. The findings of the study were published in the Journal of Science. This research also gives a better understanding of the ancestral function of these genes. It also enumerates an important step in evolutionary biology.

Bilaterian animals have a head-to-tail axis. They have largely symmetrical left and right sides and include everything from humans to dogs to fish to spiders. The roles of Hox genes in bilaterian animals have also been well established.

As the animals develop, Hox genes control the characteristic features of different segments of these animals. They set in motion the genetic programs leading to the formation of various body structures such as limbs and organs. Segment characterization depends on the expression of Hox genes or the Hox code in that region of the developing organism.

The researchers disrupted the function of the following genes,

  • Anthox1a
  • Anthrox8
  • Anthrox6a
  • Gbx

It was a two-way process. The researchers disrupted the function of Hox genes through treatment with short hairpin RNAs. They also used CRISPR-Cas9 i.e. a gene-editing system to knock out these Hox genes from the genome.

What do the researchers found?

The research team found that the loss of Hox gene or any disruption in its function causes defects in both body segmentation and tentacle patterning. The sea anemones with mutations developed only two or three tentacles. However, normal anemones usually develop four tentacles. Some tentacles were distended and partially fused, and others were bifurcated.

According to the researchers, it’s totally possible that the familial role of the Hox genes was to both drive segment formation and confer segment identity. In existing bilaterians, these functions may have divided such that Hox genes just control segment identity.

Moreover, the findings reveal the existence of a Hox code in developing cnidarians. It provides evolutionary biologists with new approaches into the process of Hox code evolution. The research team confirms the existence of these genes, before the splitting of bilaterians and cnidarians from their common ancestor.

This study opens new ways to look at more cnidarian branches to test if these genes are employed in a similar fashion. It also provides further support to the idea that evolution doesn’t necessarily make the gene code more complex.

There is a popular belief that the process of evolution leads to increased sophistication and complexity. This event of augmented complexity is inexorably upward. However, this study states that this doesn’t happen in many cases. Our prehistoric animal ancestors possessed complex biology. The same biological system is present in humans today. It is regulated by the same types of genes; it is just that the ancestral genes were just employed in a different way.



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Areeba Hussain
The author is a Medical Microbiologist and healthcare writer. She is a post-graduate of Medical Microbiology and Immunology. She covers all content on health and wellness including weight loss, nutrition, and general health.


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