Sheep's wool: Difference between revisions

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[[image: wool_cross_section.jpg | thumb | left | Figure 2. The cross-section of a wool fiber showing the arrangement of para- and ortho-cortical cells. <ref>Science Learning Hub – Pokapū Akoranga Pūtaiao, The University of Waikato Te Whare Wānanga o Waikato, www.sciencelearn.org.nz</ref>]]
[[image: wool_cross_section.jpg | thumb | 200px | left | Figure 2. The cross-section of a wool fiber showing the arrangement of para- and ortho-cortical cells. <ref>Science Learning Hub – Pokapū Akoranga Pūtaiao, The University of Waikato Te Whare Wānanga o Waikato, www.sciencelearn.org.nz</ref>]]


Cortical cells are helix shaped and generally categorised into para- and ortho- cortical cells, with meso- cortical cells having characteristics in between the para- and ortho- categories. Para-cortical cells are loosely packed and have large amounts of cystine, while ortho-cortical cells contain discrete macrofibrils and are high in tyrosine.<ref name="marshall">Marshall RC, Orwin DF, Gillespie JM. Structure and biochemistry of mammalian hard keratin. <i>Electron Microsc Rev.</i> 1991;4(1):47-83. doi:10.1016/0892-0354(91)90016-6</ref> It was previously believed that wool’s crimp was caused by the distribution of para- and ortho-cortical cells because wool fibers show well defined bilateral segmentation in the cortex.<ref name="wortmann"></ref><ref name="marshall"></ref> However, further research has disproved the association between para and ortho-cuticle cell distribution. <ref>Hynd PI, Edwards NM, Hebart M, McDowall M, Clark S. Wool fibre crimp is determined by mitotic asymmetry and position of final keratinisation and not ortho- and para-cortical cell segmentation. Animal. 2009;3(6):838-843. doi:10.1017/S1751731109003966</ref><ref name="harland">Harland DP, Vernon JA, Woods JL, et al. Intrinsic curvature in wool fibres is determined by the relative length of orthocortical and paracortical cells. J Exp Biol. 2018;221(Pt 6):jeb172312. Published 2018 Mar 22. doi:10.1242/jeb.172312
Cortical cells are helix shaped and generally categorised into para- and ortho- cortical cells, with meso- cortical cells having characteristics in between the para- and ortho- categories. Para-cortical cells are loosely packed and have large amounts of cystine, while ortho-cortical cells contain discrete macrofibrils and are high in tyrosine.<ref name="marshall">Marshall RC, Orwin DF, Gillespie JM. Structure and biochemistry of mammalian hard keratin. <i>Electron Microsc Rev.</i> 1991;4(1):47-83. doi:10.1016/0892-0354(91)90016-6</ref> It was previously believed that wool’s crimp was caused by the distribution of para- and ortho-cortical cells because wool fibers show well defined bilateral segmentation in the cortex.<ref name="wortmann"></ref><ref name="marshall"></ref> However, further research has disproved the association between para and ortho-cuticle cell distribution. <ref>Hynd PI, Edwards NM, Hebart M, McDowall M, Clark S. Wool fibre crimp is determined by mitotic asymmetry and position of final keratinisation and not ortho- and para-cortical cell segmentation. Animal. 2009;3(6):838-843. doi:10.1017/S1751731109003966</ref><ref name="harland">Harland DP, Vernon JA, Woods JL, et al. Intrinsic curvature in wool fibres is determined by the relative length of orthocortical and paracortical cells. J Exp Biol. 2018;221(Pt 6):jeb172312. Published 2018 Mar 22. doi:10.1242/jeb.172312

Revision as of 17:37, 11 December 2024

Introduction

Figure 1. A hairy and woolly coated lamb from the Romane breed, a hybrid of Berrichon du Cher (a single coated woolly breed) and Romanov (a double coated, hair producing breed)[1]

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.[2] True wool, as opposed to hair, is characterised by its high follicle density in the skin, small diameter, and high crimp [3]
The single woolly coat is recessive trait caused by the insertion of an antisense EIF2S2 retrogene[4] into the 3′ untranslated region of the IRF2BP2 gene.[1] 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 [1]. Differences in EIF2S2 expression are visible in lamb's wool: a woolly lamb has visible curls or ringlets while a hairy lamb has more of a wave pattern (Figure 1).

Wool structure and composition

All hair and wool fibers are composed of an cuticle layer of overlapping cells wrapped around a cortex. Coarse wools and many animal fibers also contain a medulla consisting of empty vacuoles.[5]
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.[5]

Figure 2. The cross-section of a wool fiber showing the arrangement of para- and ortho-cortical cells. [6]

Cortical cells are helix shaped and generally categorised into para- and ortho- cortical cells, with meso- cortical cells having characteristics in between the para- and ortho- categories. Para-cortical cells are loosely packed and have large amounts of cystine, while ortho-cortical cells contain discrete macrofibrils and are high in tyrosine.[7] It was previously believed that wool’s crimp was caused by the distribution of para- and ortho-cortical cells because wool fibers show well defined bilateral segmentation in the cortex.[5][7] However, further research has disproved the association between para and ortho-cuticle cell distribution. [8][9] Crimp is actually caused by the differences in length between para- and ortho-cuticle cells.[9]

Microbial interactions with wool

There are many microbes naturally present in sheep’s wool with >95% of bacteria found on the outer ends of the fleece and relatively few on the sheep’s skin and innermost parts of the fleece.[10]

Overpopulation of certain bacteria such as Pseudomonas aeroginosa is associated with one of wool farming’s primary concerns – blowfly infestation (also called flystrike).[11].In prolonged moisture, the protective waxy layer of sheep skin breaks down and allows P. aeroginosa and other opportunistic bacteria to multiply. This causes fleece rot – matted wool, staining or discoloration, and skin lesions. Fleece rot caused by P. aeroginosa stains the wool green.[11] Flystrike is not only encouraged by the damp conditions and vulnerable skin associated with fleece rot, the bacterial odors can attract female blowflies and stimulate oviposition. [12]

Microbial products have potential industrial applications, such as proteases being used for superwash treatment (degrading the cuticle cells so that wool can be machine washed and dried without felting)[13] This process is difficult to apply on an industrial scale and comes with concerns about the proteases damaging the entire wool fiber rather than just the cuticle. Studies[13] are being done on finding new proteases by studying microbes naturally present on wool.

Another potential application of microbial products is the use of biosurfectants to clean wool. [14]

References

  1. ↑ 1.0 1.1 1.2 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
  2. ↑ [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]
  3. ↑ Doyle EK, Preston JWV, McGregor BA, Hynd PI. The science behind the wool industry. The importance and value of wool production from sheep. Anim Front. 2021;11(2):15-23. Published 2021 May 17. doi:10.1093/af/vfab005
  4. ↑ Staszak K, Makałowska I. Cancer, Retrogenes, and Evolution. Life (Basel). 2021;11(1):72. Published 2021 Jan 19. doi:10.3390/life11010072
  5. ↑ 5.0 5.1 5.2 Wortmann, F.-J. (2009). The structure and properties of wool and hair fibres. Handbook of Textile Fibre Structure, 108–145. doi:10.1533/9781845697310.1.108
  6. ↑ Science Learning Hub – Pokapū Akoranga Pūtaiao, The University of Waikato Te Whare Wānanga o Waikato, www.sciencelearn.org.nz
  7. ↑ 7.0 7.1 Marshall RC, Orwin DF, Gillespie JM. Structure and biochemistry of mammalian hard keratin. Electron Microsc Rev. 1991;4(1):47-83. doi:10.1016/0892-0354(91)90016-6
  8. ↑ Hynd PI, Edwards NM, Hebart M, McDowall M, Clark S. Wool fibre crimp is determined by mitotic asymmetry and position of final keratinisation and not ortho- and para-cortical cell segmentation. Animal. 2009;3(6):838-843. doi:10.1017/S1751731109003966
  9. ↑ 9.0 9.1 Harland DP, Vernon JA, Woods JL, et al. Intrinsic curvature in wool fibres is determined by the relative length of orthocortical and paracortical cells. J Exp Biol. 2018;221(Pt 6):jeb172312. Published 2018 Mar 22. doi:10.1242/jeb.172312
  10. ↑ Jackson, T. A. et al. (2002) ‘Abundance and distribution of microbial populations in sheep fleece’, New Zealand Journal of Agricultural Research, 45(1), pp. 49–55. doi: 10.1080/00288233.2002.9513492.
  11. ↑ 11.0 11.1 Norris BJ, Colditz IG, Dixon TJ. Fleece rot and dermatophilosis in sheep. Vet Microbiol. 2008;128(3-4):217-230. doi:10.1016/j.vetmic.2007.10.024
  12. ↑ Emmens RL, Murray MD. The role of bacterial odours in oviposition by Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae), the Australian sheep blowfly. Bulletin of Entomological Research. 1982;72(3):367-375. doi:10.1017/S0007485300013547
  13. ↑ 13.0 13.1 Queiroga AC et al. (2007). Novel microbial-mediated modifications of wool. Enzyme and Microbial Technology. doi: 10.1016/j.enzmictec.2006.10.037
  14. ↑ Jibia SA et al. (2017) ‘Biodegradation of Wool by Bacteria and Fungi and Enhancement of Wool Quality by Biosurfactant Washing’, Journal of Natural Fibers, 15(2), pp. 287–295. doi: 10.1080/15440478.2017.1325430



Edited by Isaac Yu, student of Joan Slonczewski for BIOL 116, 2024, Kenyon College.

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