TRANSGENIC SHEEP AND WOOL GROWTH - POSSIBILITIES AND CURRENT STATUS

Merino wool is the result of generations of selection, yet improvement s in wool quality and performance are still being sought. Through gene manipulation, sheep transgenesis offers possibilities of understandin g the relationship between wool keratin protein composition and fibre structure and properties and of introducing novel changes to fibre pro perties and growth rates. We have established an efficient sheep trans genesis programme with an overall transgenic rate of 2.1% of zygotes i njected. However, by incorporating in vitro culture and assessment of injected zygotes, this equates to a transgenic rate of 13% from 516 la mbs born. With the first keratin gene construct, a wool keratin type I I intermediate filament gene, four live Fo transgenic sheep have been produced acid air express the transgene. In one of them, the highest e xpressor, phenotypic and ultrastructural changes were evident in the f leece. To improve wool growth rate by increasing the supply of cystein e to the follicle, transgenic sheep are being produced carrying the tw o genes necessary for endogenous cysteine synthesis. Three promoters h ave been tested driving the cysteine synthesis genes: two general prom oters, the Rous sarcoma virus long terminal repeat and mouse phosphogl ycerate kinase promoter, and a rumen-specific promoter from the sheep small proline-rich protein gene. To date, one transgenic sheep (bearin g the small proline-rich protein promoter constructs) has produced cys teine in the rumen, although the amount was low at 3 months of age and not detectable at 6 months.