Free Newsletters - Space News - Defense Alert - Environment Report - Energy Monitor
. 24/7 Space News .




EXO LIFE
Coelacanth genome surfaces
by Staff Writers
Boston MA (SPX) Apr 19, 2013


Researchers have sequenced the genome of the African coelacanth, an ancient-looking fish with lobed fins. Many coelacanth specimens (such as the one shown here) are on display in museums, but the organism's full genome has never before been sequenced. Photo by Alberto Fernandez Fernandez, available on Wikimedia Commons.

An international team of researchers has decoded the genome of a creature whose evolutionary history is both enigmatic and illuminating: the African coelacanth. A sea-cave dwelling, five-foot long fish with limb-like fins, the coelacanth was once thought to be extinct.

A living coelacanth was discovered off the African coast in 1938, and since then, questions about these ancient-looking fish - popularly known as "living fossils" - have loomed large. Coelacanths today closely resemble the fossilized skeletons of their more than 300-million-year-old ancestors. Its genome confirms what many researchers had long suspected: genes in coelacanths are evolving more slowly than in other organisms.

"We found that the genes overall are evolving significantly slower than in every other fish and land vertebrate that we looked at," said Jessica Alfoldi, a research scientist at the Broad Institute and co-first author of a paper on the coelacanth genome, which appears in Nature this week. "This is the first time that we've had a big enough gene set to really see that."

Researchers hypothesize that this slow rate of change may be because coelacanths simply have not needed to change: they live primarily off of the Eastern African coast (a second coelacanth species lives off the coast of Indonesia), at ocean depths where relatively little has changed over the millennia.

"We often talk about how species have changed over time," said Kerstin Lindblad-Toh, scientific director of the Broad Institute's vertebrate genome biology group and senior author. "But there are still a few places on Earth where organisms don't have to change, and this is one of them. Coelacanths are likely very specialized to such a specific, non-changing, extreme environment - it is ideally suited to the deep sea just the way it is."

Because of their resemblance to fossils dating back millions of years, coelacanths today are often referred to as "living fossils" - a term coined by Charles Darwin. But the coelacanth is not a relic of the past brought back to life: it is a species that has survived, reproduced, but changed very little in appearance for millions of years. "It's not a living fossil; it's a living organism," said Alfoldi. "It doesn't live in a time bubble; it lives in our world, which is why it's so fascinating to find out that its genes are evolving more slowly than ours."

The coelacanth genome has also allowed scientists to test other long-debated questions. For example, coelacanths possess some features that look oddly similar to those seen only in animals that dwell on land, including "lobed" fins, which resemble the limbs of four-legged land animals (known as tetrapods). Another odd-looking group of fish known as lungfish possesses lobed fins too. It is likely that one of the ancestral lobed-finned fish species gave rise to the first four-legged amphibious creatures to climb out of the water and up on to land, but until now, researchers could not determine which of the two is the more likely candidate.

In addition to sequencing the full genome - nearly 3 billion "letters" of DNA - from the coelacanth, the researchers also looked at RNA content from coelacanth (both the African and Indonesian species) and from the lungfish. This information allowed them to compare genes in use in the brain, kidneys, liver, spleen and gut of lungfish with gene sets from coelacanth and 20 other vertebrate species. Their results suggested that tetrapods are more closely related to lungfish than to the coelacanth.

However, the coelacanth is still a critical organism to study in order to understand what is often called the water-to-land transition. Lungfish may be more closely related to land animals, but its genome remains inscrutable: at 100 billion letters in length, the lungfish genome is simply too unwieldy for scientists to sequence, assemble, and analyze. The coelacanth's more modest-sized genome (comparable in length to our own) is yielding valuable clues about the genetic changes that may have allowed tetrapods to flourish on land.

By looking at what genes were lost when vertebrates came on land as well as what regulatory elements - parts of the genome that govern where, when, and to what degree genes are active - were gained, the researchers made several unusual discoveries:

+ Sense of smell. The team found that many regulatory changes influenced genes involved in smell perception and detecting airborne odors. They hypothesize that as creatures moved from sea to land, they needed new means of detecting chemicals in the environment around them.

+ Immunity. The researchers found a significant number of immune-related regulatory changes when they compared the coelacanth genome to the genomes of animals on land. They hypothesized that these changes may be part of a response to new pathogens encountered on land.

+ Evolutionary development. Researchers found several key genetic regions that may have been "evolutionarily recruited" to form tetrapod innovations such as limbs, fingers and toes, and the mammalian placenta. One of these regions, known as HoxD, harbors a particular sequence that is shared across coelacanths and tetrapods. It is likely that this sequence from the coelacanth was co-opted by tetrapods to help form hands and feet.

+ Urea cycle. Fish get rid of nitrogen by excreting ammonia into the water, but humans and other land animals quickly convert ammonia into less toxic urea using the urea cycle. Researchers found that the most important gene involved in this cycle has been modified in tetrapods.

The coelacanth genome may hold other clues for researchers investigating the evolution of tetrapods.

"This is just the beginning of many analyses on what the coelacanth can teach us about the emergence of land vertebrates, including humans, and, combined with modern empirical approaches, can lend insights into the mechanisms that have contributed to major evolutionary innovations," said Chris Amemiya, a member of the Benaroya Research Institute and co-first author of the Nature paper. Amemiya is also a professor at the University of Washington.

Sequencing the full coelacanth genome was uniquely challenging for many reasons. Coelacanths are an endangered species, meaning that samples available for research are almost nonexistent. This meant that each sample obtained was precious: researchers would have "one shot" at sequencing the collected genetic material, according to Alfoldi. But the difficulties in obtaining a sample and the challenges of sequencing it also knit the community together.

"The international nature of the work, its evolutionary value and history, and the fact that it was a technically challenging project really brought people together," said Lindblad-Toh. " We had representatives from every populated continent on earth working on this project."

Although its genome offers some tantalizing answers, the research team anticipates that further study of the fish's immunity, respiration, physiology, and more will lead to deep insights into how some vertebrates adapted to life on land, while others remained creatures of the sea.

Researchers from 40 institutions across 12 countries contributed to this work. Many funding agencies around the world provided support, including the African Coelacanth Ecosystem Programme of the South African National Department of Science and Technology, which supported the collection of samples, and the National Human Genome Research Institute, which supported the Broad Institute's contributions including genome sequencing. Paper cited: Amemiya, CT et al. "The African coelacanth genome provides insights into tetrapod evolution" Nature DOI: 10.1038/nature12027

.


Related Links
Broad Institute of MIT and Harvard
Life Beyond Earth
Lands Beyond Beyond - extra solar planets - news and science






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





EXO LIFE
Study: Lack of magnetic field could render many exoplanets lifeless
Antioquia, Colombia (UPI) Apr 17, 2013
Some Earth-like exoplanets that are seemingly habitable may be missing magnetic shielding, exposing them to damaging radiation, researchers in Colombia say. To support life as we know it, planets need thick, water-rich atmospheres and liquid surface water, Jorge Zuluaga at the University of Antioquia and colleagues said, but water can get blasted away by stellar winds unless the planet ... read more


EXO LIFE
Characterizing The Lunar Radiation Environment

Russia rekindles Moon exploration program, intends setting up first human outposts there

Pre-existing mineralogy may survive lunar impacts

Lunar cycle determines hunting behaviour of nocturnal gulls

EXO LIFE
Dutch reality show seeks one-way astronauts for Mars

Accurate pointing by Curiosity

NASA Mars Orbiter Images May Show 1971 Soviet Lander

Opportunity is in position for solar conjunction at 'Cape York' on the rim of Endeavour Crater

EXO LIFE
Mysterious water on Jupiter came from comet smash

What makes a good astronaut?

NASA urged to preserve funding for planetary science missions

Testing Spacesuits in Antarctica, part 1

EXO LIFE
Yuanwang III, VI depart for space-tracking missions

Shenzhou's Shadow Crew

Shenzhou 10 sent to launch site

China's Next Women Astronauts

EXO LIFE
Spacewalkers Deploy Plasma Experiment, Install Navigational Aid

The New and Improved ISS Facilities Brochure

Full tank, please For ATV Einstein

Russia puts mice, newts in space for a month

EXO LIFE
NASA Seeks Innovative Suborbital Flight Technology Proposals

Stephane Israel named Chairman and CEO of Arianespace

Launch pad problem scrubs launch of Antares rocket for NASA

ILS Proton Launches Anik G1 for Telesat

EXO LIFE
Kepler Discovers its Smallest Habitable Zone Planets

Notre Dame astrophysicist discovers 5-planet system like Earth

Five-Planet System With Most Earth-Like Exoplanet Yet Found

New Techniques Allow Discovery Of Smallest Super-Earth Exoplanets

EXO LIFE
US eases export rules on aerospace parts

MEADS Low Frequency Sensor Cues Multifunction Fire Control Radar in Test

Ontario Air Cadets Take Flight in Lockheed Martin's Prepar3D Simulation Software

Softening steel problem expands computer model applications




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement