Tuesday, June 8, 2010

Thrifty gene

Thrifty gene provides for survival

Source: Excegen Genetica SA, June 2010

Under dietary restriction, bovines carrying a wild type of the growth hormone gene (GH) are able to sustain body growth, whereas bovines carrying the domestic form of the gene stop growing, according to a study published in the journal Genetics and Molecular Research (GMR).

In the study, a Brazilian team compared the weight gain of cattle of the Nelore breed (Bos indicus) that carry either the common or domestic form of the GH, known as the G2 allele, or the wild type form, known as the G1 allele.

Under ad libitum conditions, G2 animals gained more weight than G1 animals. However, when food became scarce, the situation was inverted: G2 animals lost weight, whereas G1 animals maintained weight gain.

GH controls metabolism, growth, development and aging in a wide range of animals, from insects to human beings. Genetic mutations that reduce GH signaling usually increase life span and longevity in a way similar to that seen in dietary restriction models. However, the mechanisms by which dietary restriction works are poorly understood.

'Our results show that the ideal dietary regimen is just as much the consequence of genetic selection as its cause. Dietary regimens work as any selection force, in the sense of adapting the genes to given nutritional conditions', explains Sergio Dani, the scientist who led the Brazilian research team.

The G2 allele has been dubbed the 'demanding allele', because it is optimally fitted to ad libitum nutrient intake. The G1 allele has been dubbed 'the thrifty allele', because it is optimally fitted to dietary restriction.

As the thrifty allele is rare in domestic cattle, almost all animals that carry a copy of this allele also carry a copy of the demanding allele. This condition is termed heterozygosis.

'Given its recessive trend, the thrifty allele is conserved within herds even under ad libitum conditions", explains Hani Yehia, co-author of the study. 'Under ad libitum conditions, the selection against heterozygous animals is somewhat relaxed, resulting in the thrifty allele being conserved. Such heterozygous animals eventually give birth to thrifty, homozygous G1G1 animals. Under exacting conditions, these homozygous animals are fundamental for the survival of the species", concludes Yehia.

The study shows that dietary regimens per se must not increase or reduce life span or longevity: “It is all a question of adaptation to the environment. As long as there is abundant food, the demanding organisms have advantage over the thrifty ones. As soon as food becomes a prize, the demanding vanish and the thrifty thrive', explains Sergio Dani. 'When it comes to shrinking resources, it's survival of the thriftiest', he concludes.

Learn more:

. Dani S. U., Dani M. A. C., Freire, I. L., Gouvea S. P., Knackfuss F. B., Lima F. P., Mercadante M. E. Z., Monteiro E., Paggiaro S. M. G., Razook A. G., and Yehia H. C. Survival of the thriftiest: restricted nurture reveals the thrifty nature of a growth gene in Bos indicus. Genetics and Molecular Research 9 (2): 1032-1044 (2010). To obtain a free copy of the article access: http://www.funpecrp.com.br/gmr/year2010/vol9-2//pdf/gmr844.pdf

. Scientists of the following institutions colaborated in the study: Excegen Genética SA, Genon Genetica ltda., Coarana Biotecnologia ltda., Institute of Zootecnics of Sertaozinho/APTA and Federal University of Minas Gerais;

. The study was carried out at four locations in Brazil, during 7 years;

. 6864 bovines were genotyped;

. Two patents were filed with INPI/Brazil: PI 0403770-7 A (2006) e PI 0503427-2 (2007);

. The study was financed by: Excegen Genetica SA, Genon Genetica ltda., FAPEMIG, CNPq, FAPESP and SEBRAE.

. The study was supported by: Acangau Foundation, Beckhauser Troncos e Balanças, Bellman Nutrição Animal, Brascan Cattle SA, Quilombo Empreendimentos e Participações ltda., Vallée.

. More information with Sergio U. Dani: srgdani@gmail.com.

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