Scientists sequence genome of human's closest invertebrate relative

Aug 15, 2013
Botryllus schlosseri is humans' closest living invertebrate relative. Credit: Chris Patton

(Phys.org) —Botryllus schlosseri, a small sea creature, can regenerate its entire body from its blood vessels alone. Stanford researchers hope that sequencing its genome will lead to advances in regenerative and transplant medicine for humans.

At first glance, Botryllus schlosseri has very little in common with humans. The small fuses together with others to form colonies that look like psychedelic blobs, encrusting rocks and seaweeds. It can reproduce asexually, and an entire individual can be regenerated from its blood vessels alone.

And yet, Botryllus is humans' closest living invertebrate relative. (Invertebrates lack a .) Now, a group led by Stanford scientists has sequenced its genome, making it possible to find the genetic basis for some of the animal's amazing regenerative abilities and immunity features, which potentially could be applied to human medicine.

In total, the group sequenced the animal's 580 million base pairs of DNA. (The , by comparison, consists of more than 3 billion .) Though the researchers haven't studied the entire genome, they found evidence that Botryllus makes a useful invertebrate model for studying , in particular for highlighting the evolution of immunity and stem cell-mediated regeneration.

The researchers compared the Botryllus genome with several vertebrate and invertebrate  genomes. Focusing on genes involved in various human diseases – affecting things such as heart and , pregnancy and cancer – they found homologous genes for each in Botryllus, far more matches than in any of a dozen other commonly used in research.

An additional investigation of blood-related genes revealed that Botryllus was probably the first invertebrate to have vasculature in the same context of the , with blood cells traveling through blood vessels.

For example, in looking at a set of 20 genes that encode for humans' hematopoietic stem cells – cells that can self-renew and differentiate into other types of – they found 14 that are also expressed in cells isolated from the Botryllus stem cell niche. The scientists are now investigating how these genes function in Botryllus.

"The whole body can regenerate from the vasculature alone: the heart, digestive system, sophisticated tissues," said Ayelet Voskoboynik, a scientist at Stanford's Stem Cell Institute and Hopkins Marine Station, and the lead author on the study. "And it can do this relatively fast, probably using stem cells. Now that we have the genome, we can try to understand the mechanism behind it."

The study of Botryllus' genome could also lead to advances in . When two genetically distinct Botryllus colonies come into contact with each other, they either fuse their blood vessels to create a single organism, or reject one another and maintain individuality. When the between the two colonies fuse into one interconnected network, the stem cells from each partner colony begin to circulate throughout the other.

The stem cells compete and in many cases one partner's stem cells "win" – and any new or replacement tissue grown through the fused colony does so based on the "winner's" genetic code.

A similar process occurs in humans who undergo an allogeneic transplant – when a patient receives tissue or cells from a non-identical donor. For instance, if a patient receives bone marrow or a ligament graft from a donor, over time, the recipient's cells replace the donor tissue.

In some instances, particularly concerning transplants of bone marrow or hematopoietic  stem cells, the recipient's body rejects the donor cells. Voskoboynik suspects that studying the for this interaction in Botryllus could lead to improvements in human therapies.

"If we can learn what makes a highly competitive stem cell a winner, and why others are rejected, we could hope to apply that knowledge to improve the success rate of allogeneic transplantations in humans," Voskoboynik said.

An important byproduct of the research, Voskoboynik said, was that Botryllus' complicated required the team to develop a new sequencing technique. The method, which has been patented, yielded exceptionally long, accurate sequences of DNA.

Additionally, rather than creating an average of the genetic information encoded on each paired chromosome, as standard techniques do, the new method yielded individual results from each chromosome. That advance, Voskoboynik said, could play a critical role in studying human diseases that occur as the result of different versions of genes existing on paired chromosomes.

The study was recently published in the peer-reviewed journal eLIFE.

Explore further: Innovation to turn 'junk DNA' into genetic markers

More information: elife.elifesciences.org/content/2/e00569

Related Stories

Tracking nanodiamond-tagged stem cells

Aug 05, 2013

A method that is used to track the fate of a single stem cell within mouse lung tissue is reported in a study published online this week in Nature Nanotechnology. The method may offer insights into the factors that determ ...

Recommended for you

MaxBin: Automated sorting through metagenomes

Sep 29, 2014

Microbes – the single-celled organisms that dominate every ecosystem on Earth - have an amazing ability to feed on plant biomass and convert it into other chemical products. Tapping into this talent has ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Lurker2358
not rated yet Aug 15, 2013
The stem cells compete and in many cases one partner's stem cells "win" – and any new or replacement tissue grown through the fused colony does so based on the "winner's" genetic code.


Assuming regeneration is the best possible trait for continuing life, the the stem cells would need to be selected on the bases of their ability to regenerate the entire organism.

Otherwise, there would be genetic bottlenecks in all the other genes (not directly related to regeneration,) because this form of reproduction and competition, if selecting for random genes, would produce genetic bottlenecks and ultimately harm species survival.

Now if an organism is good enough at regenerating and reproducing, then it can afford to suck at a few other things and still keep a healthy population; If a superior predator bites you in half, no big deal, just grow back; If a toxic environment dissolves your flesh, the vascular tissue might get lucky enough to move to another environment and regenerate...