Expression of a Wool Intermediate Filament Keratin Transgene in Sheep Fibre Alters Structure

Alteration of the protein composition of the wool fibre via transgenesis with sheep wool keratin and keratin associated protein (KAP) genes may lead to production of fibre types with improved processing and wearing qualities. Using this approach, we have demonstrated that high level cortical-specific expression of a wool type II intermediate filament (IF) keratin gene, K2.10, leads to marked alterations in both the microstructure and macrostructure of the wool fibres, which have higher lustre and reduced crimp. Analysis of mRNA found reduced levels of transcripts from endogenous cortical type I (p < 0.05) and type II (p < 0.01) keratin IF genes and from the KAP8 (p < 0.001) and KAP2 (p < 0.01) gene families. Examination of protein composition revealed an altered ratio in the keratin type II protein family of the wool fibre cortex. Whilst the over-expressed K2.10 transgene product constituted the majority of keratin type II IF protein, it appeared unable to form heterodimers with much of the expressed endogenous keratin type I IF. In comparison with non-transgenic sheep, fewer IF microfibrils were visible in the cortical cells of fibres from transgenics. The combined effect on fibre structure was disruption of the formation of orthocortical and paracortical cells in the fibre cortex, a factor which could account for the reduction in fibre crimp. No effects upon transcript or protein levels, or fibre microstructure or macrostructure were observed in transgenic sheep expressing the transgene at lower levels, indicating that subtle changes to the gene expression profile in sheep wool follicles can be tolerated. The data here also illustrate that control over endogenous transcript levels in the cortex results when factors acting on the endogenous keratin type I, keratin type II and KAP gene sequences are sequestered by the active K2.10 transgene locus. Moreover, interference to a transcriptional hierarchy shared by keratin and KAP genes may occur prior to establishment of the orthocortical and paracortical compartments of the follicle cortex, at the level of the chromatin.