4. RESULTADOS Y DISCUSIÓN
1.3. Composición química del aceite de oliva
General Summary and Future Directions
This thesis focused on investigation of genetic variation in four KRTs. These genes were revealed to be polymorphic, and on that basis, they were further investigated to ascertain whether that genetic variation influenced wool traits.
Thirteen different regions of the four genes were investigated. This included parts of the promoter, exon 2 and exon 3 - 4 regions of KRT83; two fragments of the promoter (Promoter 1, Promoter 2) and exon 3 – 4 regions of KRT85; parts of the promoter, exon 1, exon 3 and exon 7 of KRT31, and three fragments of the promoter (Promoter 1, Promoter 2 and Promoter 3) of KRT34. It is notable that, 54 functional KRTs from 13 families have been identified in humans, so the ovine KRTs described thus far, including the four in this thesis, are likely to be only a small fraction of the number in the sheep genome. This suggests very strongly that further study is required to characterize more KRT genes in the sheep genome.
All the KRTs investigated in this study were found to be polymorphic. The number of variant sequences identified ranged from one for the KRT83 promoter and KRT85 Promoter 1 regions investigated, to five variants for the KRT83 exon 3 – 4 region. Most of the regions amplified had two variants. Most of the SNPs observed in these KRTs were synonymous, or located in promoter regions or intron regions. It could however be wrongly assumed that they may not have a functional effect, but they could effect gene expression in a variety of now well understood ways. For example, synonymous SNPs can affect mRNA stability (Duan et al., 2003), and alter mRNA secondary structure (Nackley et al., 2006). In the context of these KRTs, further investigation will therefore be required to ascertain whether SNPs of this kind do affect mRNA stability and structure, and thus function, and thus ultimately whether this disturbs the amount of mature protein produced in the wool fibre.
The results also suggest that genes coding for the keratin proteins have been conserved during evolution. It has been suggested that the evolution of the variable glycine-rich domains of keratins proceeded through a pathway that included a series of tandem duplications and possible gene conversion events (Klinge, Sylvestre, Freedberg, & Blumenberg, 1987). Interestingly, the evolutionary patterns observed in linked KRTAP gene families can be attributed to two traditional evolutionary models: concerted evolution and birth–and–death processes (Wu, Irwin, & Zhang, 2008). Overall however, the mechanisms that drive the accumulation of keratin gene variation are currently unknown. In this respect, further investigation of other ovine KRTs may be helpful to better understanding the evolution of these genes and the variation that is found in them.
The findings of this thesis could possibly form a basis for the development of gene-markers for improving fibre diameter and fleece weight. This will require more work to validate what has been observed in larger flocks of differing breed and gender, and at different sheep ages too. Variation in the KRT83 exon 3 - 4, KRT34 promoter 1 region was found to be associated with MFD, while variation in KRT85 promoter2 was associated with fibre diameter distribution, and KRT85 exon 3 - 4 and KRT31 promoter were associated with fleece weight (Chapter 3). Should such effects be identified in other breeds, extended haplotype analysis of these chromosomal regions containing these KRTs should be considered and association studies at the haplotype level may be a better option for finding genetic markers for wool traits.
It would also be important to investigate whether other K genes or other regions of the studied KRTs have similar effects on wool traits. Future studies should be carried out to ascertain whether
variation in promoter regions and intron regions affects gene expression or protein structure, and how that might ultimately affect wool traits. If useful gene-markers can be confirmed, they could be used to improve wool quality or quantity. In this context, we found that genotype BC of the KRT31 promoter region could increase CFW by 0.21 kg, compared to genotype AA, and depending on the value of that 210 grams of extra wool, this might have substantial financial benefits.
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