Sheep's wool
Introduction
Sheep (Ovis aries) have been selectively bred to continuously produce single coated wool fleece rather than coats composed of an outer hair layer and an inner wool layer.[1] True wool, as opposed to hair, is characterised by its high follicle density in the skin, small diameter, and high crimp (waviness) [2]
Genetic origin of wool
The single woolly coat is recessive trait caused by the insertion of an antisense EIF2S2 retrogene (staszak and makalowska) into the 3′ untranslated region of the IRF2BP2 gene.[3] This gene mutation creates a chimeric IRF2BP2/asEIF2S2 RNA transcript that targets the genuine sense EIF2S2 mRNA and creates EIF2S2 dsRNA that regulates the production of EIF2S2 protein [3]. Because woolly coats are caused by the non-production of EIF2S2 protein, they are a recessive trait.
Wool structure
All hair and wool fibers are composed of an cuticle layer of overlapping cells wrapped around a cortex. Many fibers also contain a medulla consisting of empty vacuoles.
Wool has a cuticle layer that is only one cell thick, while human hair, for example, has a cuticle layer up to 10 cells thick. Wool cuticle cells also have a wedge-shaped shaped cross-section as opposed to rectangular, so the exposed edge height of wool cuticle cells is about 1 um as opposed to < 0.5 um in other animal fibers (wortmann 2009).
Wool’s crimp is generally attributed to it’s cortex structure (wortmann 2009, marshall et al 1991). Highly crimped fibers have a well defined bilateral segmentation of para-cortical and ortho-cortical cells, with the ortho-cortex on the outside of the wave. Less crimped fibers have meso-cortical cells replace some of the para-cortical cells.
Microbial interactions with wool
References
- ↑ Ryder M. A survey of European primitive breeds of sheep. Ann Genet Sel Anim. 1981;13(4):381-418. doi:10.1186/1297-9686-13-4-38
- ↑ Emma K Doyle, James W V Preston, Bruce A McGregor, Phil I Hynd, The science behind the wool industry. The importance and value of wool production from sheep, Animal Frontiers, Volume 11, Issue 2, March 2021, Pages 15–23, https://doi.org/10.1093/af/vfab005
- ↑ 3.0 3.1 Demars J, Cano M, Drouilhet L, et al. Genome-Wide Identification of the Mutation Underlying Fleece Variation and Discriminating Ancestral Hairy Species from Modern Woolly Sheep. Mol Biol Evol. 2017;34(7):1722-1729. doi:10.1093/molbev/msx114
Edited by Isaac Yu, student of Joan Slonczewski for BIOL 116, 2024, Kenyon College.
