- Sea cucumbers form one class of the echinoderms that also includes
sea urchins and star fish.
- Sea cucumbers have a unique
genome structure that has the ability to regenerate damaged or lost body parts.
- Owing to this property, the sea
cucumber is a particularly promising model animal for regenerative medicine.
Sea cucumber has a
radically different skeletal structure and a genome
structure that explains the reason behind its ability to regenerate.
The research findings that identified the high-definition
genome sequence of the sea cucumber may be useful for understanding evolution
of the animal kingdom.
‘Sea cucumbers are unique among echinoderms in not having a hardened calcium exoskeleton, and in their capacity to regenerate damaged or lost body parts.’
Cucumbers - What are They?
Sea cucumbers form one class of the
echinoderms, a phylum that also includes sea urchins and sea stars ("star
fish"). Echinoderms and chordates (a closely related phylum that includes
humans) share a feature that distinguishes them from most other animals: they
are so-called deuterostomes, in which the anus, rather than the mouth, forms
first in development.
Sea cucumbers are unique among
echinoderms in not having a hardened calcium exoskeleton, and in their capacity
to regenerate damaged or lost body parts and viscera to a much greater extent
than sea urchins or sea stars
. Genetic Make up of Sea
To explore the genetic underpinnings of
these features, and to better understand the evolution of the deuterostomes,
the authors performed high-definition genomic sequencing of the sea cucumber
Apostichopus japonicus (also known as the Japanese sea cucumber), covering
about 92% of its estimated 880 megabases of DNA, including more than 30,000
genes. Unique Genome of Sea Cucumber
By comparing the genome of A. japonicus
with that of other organisms, the authors found evidence that the echinoderms
diverged from hemichordates (a small group of marine deuterostomes that
includes the acorn worms) about 533 million years ago and the sea cucumbers
split off from other the echinoderm classes about 479 million years ago.
The authors showed that while the sea
urchin genome includes 31 genes for biomineralization, critical for forming a
calcified skeleton, the sea cucumber has only seven such genes. They also found
that the sea cucumber expressed these biomineralization genes at much
lower levels throughout development, likely accounting for their softer bodies
compared to sea urchins
.As a strategy to scare off predators, sea
cucumbers can expel their viscera, which they can then regenerate within
several weeks. The authors found a group of duplicated genes, called PSP94-like
genes, that were specifically expressed in the regenerating intestines of the
sea cucumber. These genes which had no corresponding genes in other
echinoderms, suggesting that these genes may be crucial to the animals' ability
to quickly regrow their viscera.
A second group of genes, called
fibrinogen-related proteins, were also duplicated and highly expressed during
regeneration, indicating they likely contribute to this ability as well.
"The sea cucumber is a particularly
promising model animal for regenerative medicine," said Xiang, and the
availability of its genome should aid efforts to study the biology of
regeneration and determine if echinoderm regrowth can offer insights that can
be applied to human medicine.
"Our findings should also facilitate the
understanding of the requirements for sustainable utilization and effective
breeding of echinoderms, in support of the high-value sea cucumber
industry," which includes its use as a source of food and traditional
- Zhang X, Sun L, Yuan J, Sun Y, Gao Y, Zhang L, et al. The sea cucumber genome provides insights into morphological evolution and visceral regeneration, PLoS Biol (2017)https:doi.org/10.1371/journal.pbio.2003790.