Genetic researchers from the International Sheep Genomics Consortium have sequenced the complete genome of domestic sheep (Ovis aries).
Domestic sheep. Image credit: Jaime Vasquez Sapunar / CC BY-SA 2.5.
The mapping of the sheep genome is a breakthrough that could have a massive impact for the rural economy given that sheep are a major source of meat, milk and wool products.
“Sheep were one of the first animals to be domesticated for farming and are still an important part of the global agricultural economy. Understanding more about their genetic make-up will help us to breed healthier and more productive flocks,” said Prof Alan Archibald of Roslin Institute, a co-author of the paper published in the journal Science.
The team identified the genes that give sheep their fleece and uncovered features of their digestive system, which makes them so well-suited to a diet of low quality grass and other plants.
The scientists compared the sheep’s genes with those of other animals – including goats, cattle, yaks, pigs, camels, horses, dogs, mice, opossums and humans – and identified 4,850 single-copy orthologous genes from which they constructed a phylogenetic tree.
The gene-encoding proteins involved in keratinized epidermal structure development are relevant to the formation of the rumen, skin and wool.
The researchers identified a new gene called TCHHL2 (Trichohyalin-like 2). This gene is specific to mammals and would play a role in cross-linking the keratins at the rumen surface, they say.
The team also identified a previously unrecognized gene representing subfamily of the late cornified envelope (LCE) genes, and named it LCE7A. This gene is expressed in skin of sheep, cattle and goat, but not in the rumen, and under positive selection in sheep. The researchers say that the expansion of the gene is associated with the wool formation.
Furthermore, they found that the MOGAT pathway in sheep skin may facilitate wool production. MOGAT2 and MOGAT3 genes were both expressed in sheep skin, not in liver. However, in humans, MOGAT3 is an important liver enzyme-encoding gene.
The loss of MOGAT2 and MOGAT3 in liver may reduce the importance of liver in long chain fatty acid metabolism in ruminants compared to non-ruminants, according to the team.
“We investigated the completed genome to determine which genes are present in a process called gene annotation, which resulted in an advanced understanding of the genes involved in making sheep the unique animals that they are,” said study senior author Dr Brian Dalrymple of the Commonwealth Scientific and Industrial Research Organisation’s Animal Food and Health Sciences.
“Given the importance of wool production, we focused on which genes were likely to be involved in producing wool. We identified a new pathway for the metabolism of lipid in sheep skin, which may play a role in both the development of wool and in the efficient production of wool grease (lanolin).”
Sheep are also an important biomedical model, particularly in Australia, and the genomic resources built by the team will provide a strong foundation for the detailed exploration of the similarities and differences between sheep and humans at the molecular level, and hopefully lead to improved medical treatments for a number of conditions such as sepsis and asthma.
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Yu Jiang et al. 2014. The sheep genome illuminates biology of the rumen and lipid metabolism. Science, vol. 344, no. 6188, pp. 1168-1173; doi: 10.1126/science.1252806
