Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Search for clues in the flounder genome

06.02.2014
What does the Chinese flounder have in common with a bird?

They have both developed the same mechanism for determining sex over the course of evolution, and have done so completely independently of one another. This is the recent discovery made by an international team of scientists with Würzburg involvement.

The sex of any mammal – humans included – and of a number of other living beings is usually decided by a very specific combination of chromosomes: XX for female; XY for male. However, nature boasts many different ways of determining sex. In birds, most snakes, some fish, and even butterflies, for example, we find the so-called ZW/ZZ system. In this case, the females carry one W and one Z chromosome in their cells, while the males have two Z chromosomes. This is also true for the Chinese flounder Cynoglossus semilaevis – a popular edible fish from Asia, which is bred in aquaculture there and can grow up to 40 centimeters long.

Publication in Nature Genetics

An international team of scientists has now succeeded in completely decoding the genome of this species of flounder. For the first time ever they have also been able to fully sequence a W chromosome and trace its emergence over the course of evolution. Würzburg biochemist and geneticist Professor Manfred Schartl played an instrumental role in the project. Schartl is Chairman of the Department of Physiological Chemistry at the University’s Biocenter. The scientific journal Nature Genetics has now published the results of this work.

“Our work shows that in the Chinese flounder and in birds alike the same ancient chromosomes have developed into sex chromosomes over the course of evolution – the sex chromosomes have the same ancestors in both cases. And this process took place entirely independently and at different times,” is how Schartl summarizes the main finding of this work. Surprisingly, even the gene that is largely responsible for sex determination in birds – dmrt1 – has gone through a development process in the flounder that is similar to that in birds.

Sex chromosomes pose problems

When scientists try to sequence sex chromosomes, they are faced with a mountain of problems: “For one thing, these chromosomes have undergone a major degeneration process over the course of evolution. For another, they have DNA segments that are repeated extensively,” says Manfred Schartl. This makes the search for individual genes and their organization so labor-intensive and is probably also the reason why only a tiny number of Y chromosomes have so far been fully sequenced – including those in humans and chimpanzees. Even less was previously known about the genetic information of W chromosomes. For the work that has now been published researchers have fully sequenced a W chromosome for the first time ever.

There are two main reasons why the team focused in their study on a flounder: “Measured in geological time, fish are one of the living creatures that only relatively recently developed sex chromosomes,” explains Schartl. Unlike in birds, for which this point in time was some 200 million years ago, the chromosomes in fish have therefore had comparatively little time to degenerate. In addition, flounder have a comparatively small genome.

The genome of the flounder

21,516 protein-coding genes were counted by the scientists in the genome of the Chinese flounder – humans have some 20,000 to 25,000 according to the National Genome Research Network (NGFN). Roughly 197 million years ago, the flounder line developed from that of bony fish. It was not until much later, only about 30 million years ago, that the sex chromosomes of the flounder developed – long after the phylogenetic trees of mammals, birds, and fish had separated.

Around 1,000 genes are carried by the Z chromosome of flounder, while there are 317 on the W chromosome. This is much more than in birds, which possess 26 genes on the W chromosome. And also far more than in humans and chimpanzees, on whose Y chromosomes 40 to 80 intact genes can be found. “This observation suggests that the evolutionary origin of the sex chromosomes in flounder was comparatively recent,” says Schartl. Simply put, the W chromosome in flounder has not had enough time yet to degenerate in a similar fashion to the chromosomes of birds and mammals – after all, these have had several hundred million years in which to do so.

What determines sex

What ultimately determines sex? A gene on the Z chromosome that is responsible for male attributes? Or a gene on the W chromosome that turns its male carrier into a female one? Or a combination of the two? For birds, this question remains unanswered, so the research team has tried to find an answer by looking at the Chinese flounder. “The flounder lends itself to this study because it is possible with flounder to alter sexual development by exposing the offspring to higher temperatures,” says Schartl. At an ambient temperature of 22 degrees at the time of the corresponding period of development 14 percent of flounder offspring spontaneously change sex, whereas at 28 degrees this rate increases to up to 73 percent. So-called pseudo-males then develop instead of females.

In their study, the scientists crossed these pseudo-males with normal females and let the offspring grow at normal temperatures. The surprising result was a clear surplus of males. As expected, all the ZZ carriers were male, but what was not expected, however, was that 94 percent of the ZW carriers also developed into pseudo-males. “These experiments show that sex determination in flounder is controlled by a mechanism on the Z chromosome which initiates a male development,” is how Schartl explains the findings. Nevertheless, the scientists cannot rule out with absolute certainty the possibility that there is also a second mechanism, controlled by genes that also lie on the Z chromosome, which starts at high temperatures.

A chromosome is disappearing

Is the Y chromosome in humans at risk of extinction? This question has been and will continue to be addressed in science from time to time. After all, it has already lost much of its genetic information over the course of evolution. However, as researchers showed recently, this loss has slowed markedly over the past 25 million years. This suggests that the loss must have happened much earlier.

The W chromosome of the Chinese flounder has existed for around 30 million years. During this time it has lost about two thirds of its original genetic information. If this process continues at the same rate, it will take a mere ten million years for the W chromosome to reach the same state as the Y chromosome in humans currently.

From the scientists’ standpoint, this observation shows that the loss of genetic material on sex chromosomes must be an early and rapid phenomenon in their development.

“Whole-genome sequence of a flatfish provides insights into ZW sex chromosome evolution and adaptation to a benthic lifestyle”. Nature Genetics, published online on February 2, 2014. DOI: 10.1038/ng.2890

Contact

Prof. Dr. Manfred Schartl,
T: +49 (0)931 31-84149, phch1@biozentrum.uni-wuerzburg.de

Gunnar Bartsch | Uni Würzburg
Further information:
http://www.uni-wuerzburg.de

More articles from Life Sciences:

nachricht An evolutionary heads-up – The brain size advantage
22.05.2015 | Veterinärmedizinische Universität Wien

nachricht Endocrine disrupting chemicals in baby teethers
21.05.2015 | Goethe-Universität Frankfurt am Main

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Basel Physicists Develop Efficient Method of Signal Transmission from Nanocomponents

Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.

Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...

Im Focus: IoT-based Advanced Automobile Parking Navigation System

Development and implementation of an advanced automobile parking navigation platform for parking services

To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...

Im Focus: First electrical car ferry in the world in operation in Norway now

  • Siemens delivers electric propulsion system and charging stations with lithium-ion batteries charged from hydro power
  • Ferry only uses 150 kilowatt hours (kWh) per route and reduces cost of fuel by 60 percent
  • Milestone on the road to operating emission-free ferries

The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...

Im Focus: Into the ice – RV Polarstern opens the arctic season by setting course for Spitsbergen

On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.

RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...

Im Focus: Gel filled with nanosponges cleans up MRSA infections

Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.

To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International symposium: trends in spatial analysis and modelling for a more sustainable land use

20.05.2015 | Event News

15th conference of the International Association of Colloid and Interface Scientists

18.05.2015 | Event News

EHFG 2015: Securing health in Europe. Balancing priorities, sharing responsibilities

12.05.2015 | Event News

 
Latest News

Mesoporous Particles for the Development of Drug Delivery System Safe to Human Bodies

22.05.2015 | Materials Sciences

Computing at the Speed of Light

22.05.2015 | Information Technology

Development of Gold Nanoparticles That Control Osteogenic Differentiation of Stem Cells

22.05.2015 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>