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An inserted retroposon affects spermatogenesis in boars

03.05.2006
MTT Agrifood Research Finland researchers have identified the birth mechanism of an infertility problem afflicting Finnish Yorkshire pigs. A retroposon, or “jumping gene”, was found to be behind the hereditary defect giving rise to the immotile short-tail sperm defect (ISTS) in boars, by producing a mutation in the KPL2-gene in pigs.

The ISTS defect, causing sterility, was detected in Finnish Yorkshire boars for the first time in 1987. Spermatozoa of boars suffering from the defect are immotile, and the majority have tails only one third the normal length.

Last year MTT researchers traced the defect to its exact position in the KPL2-gene, which affects sperm development. With the aid of a DNA test developed at MTT the ISTS defect can be eliminated from the pig population with one hundred percent certainty.

The results were published in March in the high-ranking journal Proceedings of National Academy of Sciences USA.

Research can also provide information about humans

The pig genome is very close to the human genome, and humans also possess the KPL2-gene. MTT Principal Research Scientist Johanna Vilkki believes that changes in the same gene also affect human spermatogenesis and may cause sperm immobility.

–Further research on the KPL2-gene function can perhaps provide completely new information on factors causing infertility in humans as well. At present very few gene defects affecting spermatogenesis have been identified in humans, and the mutations that have been recognised are associated with different types of genes, Vilkki points out.

Retroposon’s function unknown

The defect causing the ”short-tail” sperm in pigs results from a retroposon, or moving segment of DNA, having positioned itself into the KPL2-gene. MTT researcher Anu Sironen explains that retroposons are found everywhere in the genomes of most organisms.

Retroposons have been well researched, but their function is not yet precisely clear. By moving from one place to another within a genome they are able to change genes and their expression, she says.

KPL2 is a large gene, Sironen notes, whose role is little understood. In addition to sperm, the gene appears expressed, for example, in other ciliated cells in the lung and trachea, and in the liver.

Future research at MTT is intended to ascertain, among other things, whether the retroposon also affects pigs in other ways. Research work is planned together with Turku University and international collaborators.

Gene defect spread by the Jampo boar

As the families of affected boars can be traced back to one boar in the early 1980’s, it is presumed that the gene mutation causing the sperm defect took place in this boar Jampo, or its ancestors. The defect has recessive inheritance, i.e. it manifests itself only if the pig has inherited defective genes from both parents. Jampo was a popular boar used for artificial insemination, and the gene defect it transmitted became widespread in the Finnish Yorkshire pig population during the 1990’s. The gene defect has not been observed in Yorkshire pigs elsewhere in the world, nor has it been found in other pig breeds.

Yorkshire boars intended for artificial insemination have been tested for the ISTS defect since 2001 using MTT’s previously developed method based on DNA-markers. Altogether 1,050 tests had been carried out by the end of last year. 30 percent of boars tested in 2001 showed themselves to be carriers of the defective gene; last year the frequency was only 17 percent.

Johanna Vilkki | alfa
Further information:
http://www.mtt.fi/english/press/pressrelease.html

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