Better Pork - February 2007

Research

Using genetic techniques to increase lean muscle mass

Silencing one of the key genes responsible for muscle mass could help improve efficiency in the swine industry and even have some benefits for human health

by KATHY ZURBRIGG

As pork researchers and producers strive to improve production efficiency by decreasing days to market, their efforts have traditionally focused on nutrition or selective breeding.

However, Dr. Serguei Golovan from the Department of Animal and Poultry Science, University of Guelph, is using genetics to increase lean muscle mass in pigs by blocking a specific gene that is associated with muscle growth.

Genes are located in the nuclei (control centre) of all the cells of an animal. Not only do they control what traits are inherited by the next generation, they also control the daily functions of all the body’s cells through a series of different actions.

(See Figure 1. in our February 2007 Issue)

Genes are composed of deoxyribonucleic acid (DNA) and are used to as templates for the formation of ribonucleic acid (RNA) strands, which create proteins for the body. These proteins are used to make structures within the cells and to make chemicals called enzymes which affect how a cell functions. Factors that disrupt the formation of RNA can disrupt a cell’s functions.

(See Figure 2. in our February 2007 Issue)

One of the key genes responsible for muscle mass is called myostatin. Normally, myostatin is active and muscle growth occurs at a regular rate, which results in what we think of as a normal amount of muscle for a species.

When myostatin is inactivated, as occurs naturally in "double-muscled" breeds of cattle such as Belgian Blue and Piedmontese, the result is an increase of lean muscle mass of around 20 per cent. In these breeds, a mutation of the genes results in a decrease in myostatin production and allows for the increased muscle growth.

While there are no naturally occurring "double-muscled" pigs, myostatin does seem to have the same effect in swine. Research has shown that low birth weight pigs have a higher level of myostatin activity in their system and therefore a lower muscle mass. Dr. Golovan's research uses a technique called ribonucleic acid interference (RNAi) to inactivate the myostatin gene in swine and create a pig with increased lean muscle mass.

His plan to block the myostatin gene would produce a similar effect to the genetic mutation that occurs in the double-muscled breeds of cattle. Interestingly, it has recently been discovered that a natural mutation using the RNAi process was shown to be responsible for the increased lean muscle found in Texel sheep.

Dr. Golovan must hopes to perfect the RNAi technique and so he is first testing it on pig cells in the laboratory. The results look positive. Dr. Golovan's graduate student, Candace Stewart, was able to achieve almost complete silencing of the myostatin gene within pig cells and is now investigating whether it would be possible to silence the gene in mice.

Dr. Golovan's work could well improve production efficiency in the swine industry and may also offer some benefits for human health. A pig with a silenced myostatin gene could be used as a model to study muscle-related human disorders, such as muscular dystrophy.

Funding for this project is provided by Ontario Pork, the Ontario Ministry of Agriculture, Food and Rural Affairs and National Sciences and Engineering Research Council of Canada. BP

Kathy Zurbrigg is animal health and welfare specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, based in Fergus.