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Genetics

Targeting sheep

Nature volume 405, pages 1004–1005 (2000)Cite this article

Over the past few thousand years, the physical characteristics of sheep and their underlying genetic make-up have been slowly altered by selective breeding from animals with desirable characteristics. The result is that sheep are now mobile protein factories that can survive in harsh environments and still provide abundant quantities of milk, meat and wool. But although our ancestors succeeded in significantly altering this species, selective breeding is limited by the pool of desirable variants in the sheep population. Transgenic technology, developed over the past 15 years, has begun to address this problem. But, although this approach can be used to add new genetic information, it is not possible to specifically modify the genes of the species itself by this route. McCreath and colleagues, writing on page 1066 of this issue1, have finally overcome this problem by making use of the now familiar technique of cloning.

Transgenic technology has been widely applied to livestock species because it is technically quite simple, requiring only the injection of ‘naked’ DNA — unencumbered by its protein partners — into the nucleus of a fertilized egg2. Genes encoding useful human proteins such as α1-antitrypsin (an enzyme that is mutated in the disorder familial emphysema) have been inserted into sheep eggs in this way, resulting in transgenic sheep that express the human protein in their milk3. But despite the ease with which transgenic animals can be generated, this technology has limitations, because the injected DNA integrates randomly into the sheep genome. Often the injected DNA does not land in a site in the genome that allows the foreign gene (transgene) to be expressed in the desired tissue or at the appropriate level. Moreover, the sheep's endogenous genes cannot be specifically altered using this technique.

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Figure 1: Modifying specific genes in sheep.

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Authors and Affiliations

  1. Department of Molecular and Human Genetics, Howard Hughes Medical Institute, Baylor College of Medicine, One Baylor Plaza, Houston, 77030-3498, Texas, USA

    Milind Suraokar & Allan Bradley

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  1. Milind Suraokar
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  2. Allan Bradley
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Correspondence to Milind Suraokar.

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Suraokar, M., Bradley, A. Targeting sheep. Nature 405, 1004–1005 (2000). https://doi.org/10.1038/35016670

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