Sheep's wool: Difference between revisions

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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
</ref> Crimp is actually caused by the differences in length between para- and otho-cuticle cells.<ref name="harland"></ref>
</ref> Crimp is actually caused by the differences in length between para- and ortho-cuticle cells.<ref name="harland"></ref>


==Microbial interactions with wool==
==Microbial interactions with wool==

Revision as of 04:19, 11 December 2024

Introduction

Figure 1. A lamb displaying a woolly coat. By Jakub Halun
Figure 2. A lamb displaying a hairy coat. By H. Zell

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 [2]
The single woolly coat is recessive trait caused by the insertion of an antisense EIF2S2 retrogene[3] into the 3′ untranslated region of the IRF2BP2 gene.[4] 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 [4]. The difference is visible in lamb's wool, where a woolly lamb has visible curls and a hairy lamb has of a wave pattern.

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.
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]

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.[6] 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][6] However, further research has disproved the association between para and ortho-cuticle cell distribution. [7][8] Crimp is actually caused by the differences in length between para- and ortho-cuticle cells.[8]

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.[9]

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)[10] 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[10] are being done on finding new proteases by studying microbes naturally present on wool.

References

  1. ↑ 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
  2. ↑ 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
  3. ↑ Staszak K, Makałowska I. Cancer, Retrogenes, and Evolution. Life (Basel). 2021;11(1):72. Published 2021 Jan 19. doi:10.3390/life11010072
  4. ↑ 4.0 4.1 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
  5. ↑ 5.0 5.1 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. ↑ 6.0 6.1 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
  7. ↑ 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
  8. ↑ 8.0 8.1 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
  9. ↑ 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.
  10. ↑ 10.0 10.1 Queiroga, Ana & Manuela, M & Pintado, F & Malcata,. (2007). Novel microbial-mediated modifications of wool. Enzyme and Microbial Technology. doi: 40. 10.1016/j.enzmictec.2006.10.037.



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

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