Scientists have now sequenced and analyzed the genome of the simplest multicellular organism
Published on 9. Juli 2010, 00:00 h
The green alga Volvox carteri as a model system for molecular studies on the evolution of multicellular organisms
An international team of scientists from Canada, Germany, Japan, and the United States have sequenced and analyzed he genome of the simplest multicellular organism, the green alga Volvox carteri. In the journal Science, the research team reports how this model organism, a small spherical pond dweller, helps us to understand the evolution from unicellular to multicellular organisms on the molecular level. A team from Germany at Bielefeld University under Professor Dr. Armin Hallmann was decisively involved in this work.
How does a multicellular organism evolve from a unicellular organism? In the unicellular organism, all tasks to survive and reproduce have to be performed by one and the same cell, because only one cell forms the entire organism. One of the greatest achievements in the evolution of complex life forms was the transition from unicellular organisms to multicellular organisms with different cell types. In multicellular organisms like humans, a large number of cells form a cooperating cell community with specialized cell types and a division of labour among the various cells. Finding out how unicellular organisms can develop into multicellular organisms over the course of evolution is a central issue in biological research.
What's so interesting about the green alga Volvox in this context? Volvox is conceivably the most simple multicellular organism and consists of only two different cell types , which makes numerous molecular studies easier to perform. Volvox possesses 2000 small biflagellate somatic cells that form the functional organism and 16 large reproductive cells responsible for producing offspring. In addition, it has a very close, unicellular relative: the green alga Chlamydomonas. This fortunate circumstance allows the researchers to compare both organisms on the molecular level. In addition, the evolutionary changes during the development of Volvox from a Chlamydomonas-like ancestor reveal clear parallels in other multicellular lineages. These were the decisive reasons for choosing Volvox as a model system for studying the evolution of multicellular organisms.
Volvox was first described by the Dutch biologist Antoni van Leeuwenhoek more than 300 years ago. However, van Leeuwenhoek classified these multicellular, spherical, flagellated green algae as microscopic little animals (Animalcules), largely due to their temperamental swimming behaviour. The name of this photogenic fresh water alga comes from the Latin verb volvere (to roll or revolve) because Volvox rotates on its own longitudinal axis when swimming forward. You can find Volvox in ponds and ditches almost anywhere in the world, although it prefers warmer water. With a diameter of up to 2 mm, you can recognize the alga with the naked eye.
An international group of scientists has now sequenced and analyzed the genome of Volvox carteri. It consists of approximately 140 million base pairs and contains about 14,500 genes, the authors tell us in the journal Science. Humans have a maximum of 25,000 genes, and thus not even twice as many as Volvox. After sequencing, the researchers compared the genome of the multicellular green alga with that of its unicellular relative Chlamydomonas, which had already been sequenced in 2007. The researchers wanted to find out how the genetic repertoire of the simplest multicellular organism differs from that of the unicellular organism.
"We were really surprised to see how small the differences are between the genome of the unicellular Chlamydomonas and that of the multicellular Volvox," said Professor Armin Hallmann, molecular biologist and algae researcher at Bielefeld University. "Despite great differences in both the complexity of the two organisms and their life cycles, their genomes both possess similar protein-coding potentials. We have found very few genes that are specific to Volvox. Evidently, what is decisive is how and when genes are transcribed and translated into proteins. It is not essential to have a dramatic increase in the number of genes in order to evolve from a unicellular to a multicellular organism."
The sequencing and analysis of the Volvox genome is a major step towards understanding the molecular "toolbox" underlying the evolution from unicellular to multicellular organisms. In the long term, the study of molecular processes in simple organisms should lead us to a better understanding of the developmental history and key functions of far more complex life forms such as humans .
Original publication:
Prochnik, S.E., Umen, J., Nedelcu, A., Hallmann, A., et al: Genomic analysis of organismal complexity in the multicellular green alga Volvox carteri. Science (9. Juli 2010)
www.uni-bielefeld.de/biologie/Zellbiologie
An international team of scientists from Canada, Germany, Japan, and the United States have sequenced and analyzed he genome of the simplest multicellular organism, the green alga Volvox carteri. In the journal Science, the research team reports how this model organism, a small spherical pond dweller, helps us to understand the evolution from unicellular to multicellular organisms on the molecular level. A team from Germany at Bielefeld University under Professor Dr. Armin Hallmann was decisively involved in this work.
The simplest multicellular organism: the green alga Volvox carteri (Photo: Armin Hallmann)
How does a multicellular organism evolve from a unicellular organism? In the unicellular organism, all tasks to survive and reproduce have to be performed by one and the same cell, because only one cell forms the entire organism. One of the greatest achievements in the evolution of complex life forms was the transition from unicellular organisms to multicellular organisms with different cell types. In multicellular organisms like humans, a large number of cells form a cooperating cell community with specialized cell types and a division of labour among the various cells. Finding out how unicellular organisms can develop into multicellular organisms over the course of evolution is a central issue in biological research.
What's so interesting about the green alga Volvox in this context? Volvox is conceivably the most simple multicellular organism and consists of only two different cell types , which makes numerous molecular studies easier to perform. Volvox possesses 2000 small biflagellate somatic cells that form the functional organism and 16 large reproductive cells responsible for producing offspring. In addition, it has a very close, unicellular relative: the green alga Chlamydomonas. This fortunate circumstance allows the researchers to compare both organisms on the molecular level. In addition, the evolutionary changes during the development of Volvox from a Chlamydomonas-like ancestor reveal clear parallels in other multicellular lineages. These were the decisive reasons for choosing Volvox as a model system for studying the evolution of multicellular organisms.
Volvox was first described by the Dutch biologist Antoni van Leeuwenhoek more than 300 years ago. However, van Leeuwenhoek classified these multicellular, spherical, flagellated green algae as microscopic little animals (Animalcules), largely due to their temperamental swimming behaviour. The name of this photogenic fresh water alga comes from the Latin verb volvere (to roll or revolve) because Volvox rotates on its own longitudinal axis when swimming forward. You can find Volvox in ponds and ditches almost anywhere in the world, although it prefers warmer water. With a diameter of up to 2 mm, you can recognize the alga with the naked eye.
An international group of scientists has now sequenced and analyzed the genome of Volvox carteri. It consists of approximately 140 million base pairs and contains about 14,500 genes, the authors tell us in the journal Science. Humans have a maximum of 25,000 genes, and thus not even twice as many as Volvox. After sequencing, the researchers compared the genome of the multicellular green alga with that of its unicellular relative Chlamydomonas, which had already been sequenced in 2007. The researchers wanted to find out how the genetic repertoire of the simplest multicellular organism differs from that of the unicellular organism.
"We were really surprised to see how small the differences are between the genome of the unicellular Chlamydomonas and that of the multicellular Volvox," said Professor Armin Hallmann, molecular biologist and algae researcher at Bielefeld University. "Despite great differences in both the complexity of the two organisms and their life cycles, their genomes both possess similar protein-coding potentials. We have found very few genes that are specific to Volvox. Evidently, what is decisive is how and when genes are transcribed and translated into proteins. It is not essential to have a dramatic increase in the number of genes in order to evolve from a unicellular to a multicellular organism."
The sequencing and analysis of the Volvox genome is a major step towards understanding the molecular "toolbox" underlying the evolution from unicellular to multicellular organisms. In the long term, the study of molecular processes in simple organisms should lead us to a better understanding of the developmental history and key functions of far more complex life forms such as humans .
Original publication:
Prochnik, S.E., Umen, J., Nedelcu, A., Hallmann, A., et al: Genomic analysis of organismal complexity in the multicellular green alga Volvox carteri. Science (9. Juli 2010)
Contact:
Professor Dr. Armin
Hallmann, Universität Bielefeld
Fakultät für Biologie der Universität
Bielefeld
Tel: 0521 106-5592
Email:
armin.hallmann@uni-bielefeld.de
www.uni-bielefeld.de/biologie/Zellbiologie
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