How Hydra – a group of small aquatic animals – regenerates their own heads


Hydra. Credit: David Plachetzki

A new paper in Biology and evolution of the genome, published by Oxford University Press, shows for the first time how Hydra, which are a group of small aquatic animals, can regenerate their own heads by changing the way their genes are regulated, called epigenetics.

Hydra belong to the group of animals which includes about 10,000 species divided into two main groups: anthozoa (comprising sea anemones, corals and sea feathers) and jellyfish (marine wasps, jellyfish and hydras). Hydra, which live in temperate and tropical regions, are generally considered biologically immortal; Hydra stem cells have an unlimited capacity for self-renewal.

Regeneration of the whole body occurs in some animal species. The extent to which the genes and regulatory networks of genes responsible for regeneration vary from species to species remains largely unexplored. Scientists still do not understand the mechanism that drives Hydra head regeneration. Previous studies have found evidence of regulation by multiple developmental pathways. Researchers have discovered several genes associated with regeneration of the head.

To understand the basics of controlling Hydra regeneration of the head, the researchers first identified 27,137 active elements in one or more sections of the body of the organism or in regenerating tissues. The researchers used the modified histone ChIP-seq, a method used to analyze how proteins interact with DNA, to identify respectively 9998 candidate proximal promoter and 3018 candidate activator-type regions. Their research shows that a subset of these regulatory elements is remodeled during head regeneration and identifies a set of enriched transcription factor motifs in regions activated during head regeneration. These enriched motifs included developmental transcription factors.

This work identifies for the first time the candidate genome-specific regulatory elements that change during Hydra head regeneration, which determines the development of organisms by turning genes on or off as needed. “An interesting finding from this work is that the head regeneration and budding programs in Hydra are quite different, said the document’s lead author, Aide Macias-Muñoz. “Even if the result is the same (a Hydra head), gene expression is much more variable during regeneration. Dynamic gene expression is accompanied by dynamic chromatin remodeling at sites where developmental transcription factors bind. These results suggest that complex development activators were present before the split of Cnidaria and Bilateria. “

Reference: “Coordinated gene expression and chromatin regulation during Hydra head regeneration” December 8, 2021, Biology and evolution of the genome.
DOI: 10.1093 / gbe / evab221


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