Hans Zauner

**This week in *GigaScience* we published the [genome of the
mediterranean cone snail, *Lautoconus
ventricosus*](https://doi.org/10.1093/gigascience/giab037). Cone snails
produce a wide variety of powerful toxins and the new chromosome-scale
genome assembly opens the door for detailed investigations of their
diversity and evolution.**

Cone snails are beloved by collectors for their often beautiful shells,
but they are infamous because of their powerful venom. As predatory
species, they hunt marine worms or even small fish by firing a
toxin-charged harpoon (a modified tooth) at their victims. This might
also explain why many of the conotoxins are so powerful: the snails need
to paralyze their victims quickly, or otherwise their lunch might get
away.

Worldwide, there are more than 900 species of cone snails and the venom
of certain larger species can kill a human. However, for their
sequencing project, [Rafael
Zardoya](https://www.mncn.csic.es/es/quienes_somos/zardoya-san-sebastian-rafael)
and colleagues chose a smaller species, which is harmless to humans: the
mediterranean cone snail *Lautoconus ventricosus*.

" *The species* Lautoconus ventricosus *is the cone snail endemic to the
Mediterranean Sea and the Atlantic Ocean region near to the Gibraltar
strait.*", Zardoya explains, adding: *"Although its olive-colored shell
is not as stunning as those of cone snails from the Indo-Pacific region,
it is one of the earliest cone snails described and has a long taxonomic
history.*"

<figure class="wp-block-image size-large is-resized">
<img
src="http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/medConeSnail-1024x770.jpg"
class="wp-image-3986" loading="lazy" decoding="async"
srcset="http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/medConeSnail-300x226.jpg 300w, http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/medConeSnail-768x577.jpg 768w, http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/medConeSnail.jpg 1124w"
sizes="(max-width: 542px) 100vw, 542px" width="542" height="406" />
<figcaption>Lautoconus ventricosus. photo:
Manuel Tenorio</figcaption>
</figure>

[Manuel Tenorio](https://www.conchology.be/?t=9001&id=29995), also an
author of the paper, explains the background to the project: "*We have
been working on different aspects of cone snail biology for more than a
decade. We have focused our interests on the West African region, a
hotspot of cone snail diversity, but also work on cone snails from other
parts of the world. Sampling the local species, abundant in southern
Spain and Portugal was straightforward. Furthermore, we managed to keep
specimens of L. ventricosus alive in aquarium where they have adapted
pretty well. We feed them with live bait, and they have been able to
reproduce in captivity. This will certainly be very useful for future
developmental biology studies, currently in progress."*

Conotoxins (that is, the venoms of cone snails) are a family of usually
smallish peptides of around 10-30 amino acids in length. They are very
precise in their action and can be sorted into groups according to their
molecular targets, various ion channels. Their precise and potent
effects make conotoxins also interesting for pharmacological
researchers. For example, one conotoxin-derived drug (Ziconotide) is
approved for medical use and is given to patients who need powerful pain
release. Ziconotide blocks one specific type of ion channel, the *N-type
voltage gated calcium channel*, and thereby inhibits the release of
neurochemicals in the nervous system. Used as a pain reliever, the
substance is magnitudes more powerful than morphine.

What makes conotoxins so fascinating is their diversity: not only is
there a large variety between species, but also the venom gland of one
individual specimen typically contains not one but dozens, if not
hundreds, of structurally different peptides, with a large variety of
precursors encoded in the genome. Why is that so? Tenorio explains:

*"Cone snails belong to the superfamily Conoidea, a remarkably
biodiverse group of venomous marine invertebrates comprising more than
10000 species. Conoidea are successful top predators in the marine realm
thanks to the venom, a key evolutionary innovation. They have
diversified through recurrent evolutionary radiations. Venom peptides
diverge at a very high rate in a continuous arms race (red queen
strategy) to adapt to changes in their targets in the prey*. "

Seen through the lens of evolutionary theory, whenever there are
predators and prey, there's usually an arms race. Producing a cocktail
of different, fast-changing toxins gives the predators a temporary
advantage. A trajectory towards resistance against one stable toxin
might exist, but evolving lasting countermeasures to a diverse, rapidly
changing spectrum of toxins is not so straightforward.

To add further complexity, functional diversity arises also due to
downstream modifications at the transcriptional and protein level.
Therefore, to understand the function and evolution of conotoxins, the
entire toolkit of modern biology is needed: genomics, transcriptomics,
and proteomics. A chromosome scale reference genome, such as the one
published now in *GigaScience*, is a crucial element to bring it all
together.

The new genome assembly is one of the largest gastropod genomes
sequenced so far, with 3.59 billion base pairs organized in 35
chromosomes. The authors annotated 32,675 protein coding genes.

The Spanish scientists also explored the transcriptome, specifically of
the venom gland, and identified 289 transcripts that could be assigned
to known conotoxin precursor families. Mapping these transcripts to the
reference genome, the overall picture is that venom precursor genes are
not clustered, but distributed over the entire genome, although with
some traces of past "tandem" duplication events.

<figure class="wp-block-image size-large">
<img
src="http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/genomeorganiz.jpg"
class="wp-image-3987" loading="lazy" decoding="async"
srcset="http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/genomeorganiz.jpg 716w, http://gigasciencejournal.com/blog/wp-content/uploads/2021/05/genomeorganiz-300x274.jpg 300w"
sizes="(max-width: 716px) 100vw, 716px" width="716" height="655" />
<figcaption><a href="https://doi.org/10.1093/gigascience/giab037">Genome
organization of L. ventricosus.</a></figcaption>
</figure>

Zardoya: *"For many years, it was puzzling how the great diversity of
toxins was generated. The genome answers this question. Many gene copies
distributed throughout the different chromosomes are producing this
diversity, which is later enhanced by post-translational modifications
of the peptides. "*

 
Another group recently also published a chromosome-level genome of a
different cone snail species, [*Conus
betulinus*](https://www.nature.com/articles/s41421-021-00244-7).
Together with the genomes of other venomous animals, such as the
[Solenodon](https://doi.org/10.1093/gigascience/giy025) and the
[Cobra](https://www.nature.com/articles/s41588-019-0559-8), evolutionary
biologists can now have a closer look at the origins of venoms in
various animal branches.

Tenorio: *"As more high-quality genomes of venomous species in the
different branches of the Animal Tree of Life are assembled, we will be
able to discern which venoms are inherited through common ancestry and
which ones appear due to convergence in the different lineages."*

## References {#references .wp-block-heading}

**The genome of the venomous snail Lautoconus ventricosus sheds light on
the origin of conotoxin diversity** José Ramón Pardos-Blas, Iker
Irisarri, Samuel Abalde, Carlos M L Afonso, Manuel J Tenorio, Rafael
Zardoya *GigaScience*, 2021
<https://doi.org/10.1093/gigascience/giab037>

**Data in GigaDB**: <http://dx.doi.org/10.5524/100892>

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This week in
 
 GigaScience
 
 we published the genome of the mediterranean cone snail,
 
 Lautoconus ventricosus
 
 . Cone snails produce a wide variety of powerful toxins and the new chromosome-scale genome assembly opens the door for detailed investigations of their diversity and evolution.

Cone snails are beloved by collectors for their often beautiful shells, but they are infamous because of their powerful venom.

Rogue Scholar Posts

Cone snail genome sheds light on venom evolution