Transgenic sheep and wool growth: possibilities and current status

Abstract

Merino wool is the result of generations of selection, yet improvements in wool quality and performance are still being sought. Through gene manipulation, sheep transgenesis offers possibilities of understanding the relationship between wool keratin protein composition and fibre structure and properties and of introducing novel changes to fibre properties and growth rates. We have established an efficient sheep transgenesis programme with an overall transgenic rate of 2.1% of zygotes injected. However, by incorporating in vitro culture and assessment of injected zygotes, this equates to a transgenic rate of 13% from 516 lambs born. With the first keratin gene construct, a wool keratin type II intermediate filament gene, four live F0 transgenic sheep have been produced and all express the transgene. In one of them, the highest expressor, phenotypic and ultrastructural changes were evident in the fleece. To improve wool growth rate by increasing the supply of cysteine to the follicle, transgenic sheep are being produced carrying the two genes necessary for endogenous cysteine synthesis. Three promoters have been tested driving the cysteine synthesis genes: two general promoters, the Rous sarcoma virus long terminal repeat and mouse phosphoglycerate kinase promoter, and a rumen-specific promoter from the sheep small proline-rich protein gene. To date, one transgenic sheep (bearing the small proline-rich protein promoter constructs) has produced cysteine in the rumen, although the amount was low at 3 months of age and not detectable at 6 months.