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Mirror carp with gene in reserve

A duplicated gene provides the mirror carp with a back-up copy that protects against the effects of mutations and ensures sparse squamation.


Tübingen (Germany) September 3, 2009. Thanks to its good flavour, lack of scales and high back that fills the plate, the mirror carp has been a popular food fish for millennia. Scientists at the Max Planck Institute for Developmental Biology in Tübingen have now uncovered the secret behind a component of its domestication – the lack of scales. The phenomenon is explained by a gene duplication. While one copy of a gene, which is required for many different functions, is mutated and therefore causes the scale reduction seen in the mirror carp, the intact copy guarantees the fish’s survival. The researchers have thereby proven how reserve genes play an important role in the evolution and domestication of species. (Current Biology, October 13, 2009/advance online publication on September 3, 2009).

Mirror carp with its characteristic scale reduction, Photo: Miklós Bercsényi/Max Planck Institute for Developmental BiologyThe mirror carp is a popular fish, not just with anglers. Cooks also appreciate it for its almost entire lack of scales, which makes it considerably easier to prepare than other types of fish. This “user-friendly” characteristic harks back to medieval monks who bred them in their monasteries. Several centuries later, a group of scientists working at the Max Planck Institute for Developmental Biology in Tübingen have now uncovered the secret behind this characteristic of this breed. They discovered that a mutation in one single gene can prevent the formation of scales. This gene codes for the fibroblast growth factor receptor 1. What amazed the biologists, however, was the fact that, despite this, the fish remains viable. This receptor is, after all, involved in many important processes relating to embryonic development. Thus, a mutation should therefore actually cause serious problems. Mice embryos with defects in this gene, for instance, do not develop. This gene is also essential for survival in humans. If its function is partially impaired, it gives rise to a genetic disorder known as Kallmann syndrome, which is associated with a decreased ability to smell as well as deficiencies of the testes or ovaries.

Nicolas Rohner catches zebrafish for his experiment, Photo: Bernd Schuller/Max Planck Institute for Developmental BiologyThe mutation in this gene, however, does not appear to affect the mirror carp. Nicolas Rohner (30) and Matthew Harris in Christiane Nüsslein-Volhard’s team, studied the genotype of the zebrafish (Danio rerio) and came up with an explanation: the fish have two almost identical copies of the gene in question, one of which is the mutated version causing the lack of scales. The other copy is not mutated. It acts as a kind of “genetic back-up copy” and hinders the negative effects of its defective twin gene during the early phase of embryonic development. It switches off, however, shortly before the fish embryo forms scales: only the mutated gene is active thereafter and, as a result, the fish does not develop many scales.
 
Owing to their short generation time and undemanding way of life, zebrafish make very popular model organisms for genetic studies, Photo: Bernd Schuller/Max Planck Institute for Developmental Biology“If two genes share a certain task that is originally only performed by one gene, nature can 'afford' to mutate important genes itself. As a result, new characteristics can be induced in the organism. This mechanism appears to be an important driving force behind the incredible variety that exists in the species of fish,” explains Rohner.

Many genes in the human also arise in various numbers of copies where they affect the expression of various morphological characteristics as well as the vulnerability to certain diseases.



Original publication:
Nicolas Rohner, Miklós Bercsényi, László Orbán, Maria E. Kolanczyk, Dirk Linke, Michael Brand, Christiane Nüsslein-Volhard, Matthew P. Harris: Duplication of fgfr1 permits Fgf signaling to serve as a target for selection during domestication. Current Biology, October 13, 2009, advance online publication September 3, 2009; doi: 10.1016/j.cub.2009.07.065

Contact:
Nicolas Rohner
Phone: +49 7071-601-401
Email: Nicolas.Rohner(at)tuebingen.mpg.de

Matthew Harris
Phone; +49 7071-601-301
Email: Matthew.Harris(at)tuebingen.mpg.de

Susanne Diederich (Press and Public Relations)
Phone: +49 7071-601-333
Email: presse(at)tuebingen.mpg.de


Nicolas Rohner catches zebrafish for his experiment, Photo: Bernd Schuller/Max Planck Institute for Developmental Biology

Nicolas Rohner catches zebrafish for his experiment, Photo: Bernd Schuller/Max Planck Institute for Developmental Biology

Owing to their short generation time and undemanding way of life, zebrafish make very popular model organisms for genetic studies, Photo: Bernd Schuller/Max Planck Institute for Developmental Biology

Owing to their short generation time and undemanding way of life, zebrafish make very popular model organisms for genetic studies, Photo: Bernd Schuller/Max Planck Institute for Developmental Biology

Mirror carp with its characteristic scale reduction, Photo: Miklós Bercsényi/Max Planck Institute for Developmental Biology

Mirror carp with its characteristic scale reduction, Photo: Miklós Bercsényi/Max Planck Institute for Developmental Biology