Casein is the major protein component of milk and is an important contributor to its nutritional value and processing properties. Bovine milk contains four casein proteins that aggregate into large colloidal micelles, which give milk its particular functional characteristics. In an Advance Online Publication in Nature Biotechnology, Brigid Brophy and colleagues at AgResearch, Ruakura Research Centre in New Zealand, describe the use of transgenic and nuclear transfer technologies to create cloned cows with altered casein production (Nature Biotechnology, doi;10.1038/nbt783, January 27, 2003).

Brophy et al. engineered female bovine fetal fibroblasts to express transgenes encoding two types of casein: bovine β-casein and κ-casein (CSN2 and CSN3 genes). The modified cell lines were used to create eleven cloned calves. Milk from the cloned animals was enriched for β- and κ-casein, demonstrating the potential of this technology to make better milk.

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