The Research On Molecular Mechanism Of Affecting Wool Fibres And Follicles Structure And Economic Character

In nature, animal and plant phenotypes are the result of both genetic and environmental effects. This is also true for economically important species involved in agricultural production, such as the sheep. With respect to wool production in sheep, the large variety of breeds illustrates the influence of genetics on fibre and fleece production and many studies have investigated the effects of altered production environments on the normal wool growth phenotype. In addition to the usual genetic variants, natural mutations also produce individuals with novel phenotypes that are not typical for the species. We have investigated one such mutation in sheep, the Felting Lustre (FL) mutation, that was reported in Australian Merino (Short, 1958; McGuirk and Short, 1967), Texan Merino (Warwick et al, 1960; referred to as"Silky") and New Zealand Romney sheep (Blair, 1989, 1990). Wool produced in the adult Merino FL mutant is shiny or lustrous, lacks crimp and felts seven times faster than normal Merino wool. Interestingly, the"birth-coat"portion of the wool in FL lambs is quite straight, the early post-natal (pre-weaning) portion is crimped while the post-weaning portion is crimpless (Short, 1958). For the adult fleece, while lustre is a desirable trait, felting represents a major impediment to the use of FL wools in apparel manufacture. Indeed, post-farm chemical processing treatments required to smoothen the native surface of wool fibres and reduce garment shrinkage come at a considerable environmental and financial cost.This phenotype was described 50 years ago to result from the mutation of a single gene but the molecular and cellular basis of the properties of the wool is not well understood. Consequently, we undertook closer examination of this mutant at the level of gene expression in the wool follicle cortex and cuticle, in order to dissect the property of felting of the mutant fibres and to possibly achieve a greater understanding of the molecular events responsible for the very costly problem of garment shrinkage.The results described here suggest that alterations in the levels of both glycine/tyrosine-rich and cysteine-rich proteins in the wool fibre cortex contribute to molecular and ultrastructural changes that can account for the physical properties of the felting lustre fibres.In this study, follicle and fibre material of FL mutant (n=3) and normal control (n=5) Merino ewes was compared using histological analysis, SDS-PAGE, real-time PCR (qPCR) and electron microscopy (SEM and TEM). Histological examination suggested that follicle structure in FL mutants is essentially normal, while SDS-PAGE analysis found some low molecular weight proteins were present at much lower levels in FL wool. Examination of transcript prevalence revealed that genes KAP6.1 and KAP7 and KAP8 in felting lustre mutant follicles are down-regulated, while the KAP2.12 and KAP4.2 genes are up-regulated. TEM analysis indicated that there is only one type of cortical cell, the paracortical cell, in the fibre of felting lustre mutants while there are two kinds of cells, paracortical and orthocortical cells in fibres of normal control sheep. In contrast, SEM showed that the fibre surface of FL wool is normal. The evidence presented here strongly suggests that the properties of FL wool can be ascribed at least in part, to the lower content of high glycine/tyrosine proteins and the influence of that lower abundance on the normal proportion of orthocortical cells in mutant wool fibres. Given that lustrous Lincoln wools lack crimp and that straightening of Merino wools by transgenesis and by the FL mutation each create lustre, we reason that the lustrous appearance is a result of fibre straightening and consequent increase in the mono-directional reflectivity of the fibre surface. We have demonstrated here that disruption of the normal cortical gene expression profile is sufficient to alter cortical cell ultrastructure, to prevent bilateral segmentation of the cortex into orthocortex and paracortex and in turn, to prevent fibre crimp. Perturbation of structure in cells destined to be orthocortex in FL mutants, and in cells destined to be either orthocortex or paracortex in transgenic sheep, has the same effect on crimp and occurs at the commencement of terminal differentiation.While natural mutations such as the FL mutation can affect wool quality, the influence of the environment through nutrition during wool growth, including the availability of certain trace elements, can also have a significant effect (References). In the current study, we have thus investigated the influences of trace elements on wool quality and nutrition state in local sheep populations. To achieve this, the elements Fe, Cu, Zn, Co, S in wool were assayed by atomic absorption. Collection wool samples from mid-side skin of 30 sheep, they were belong to 4 breeds including Hetian sheep (Pure plain Hetian, Pure mountain Hetian and New Hetian three strains), Karakul sheep (Silkworm, girdle-type and rib-type three flower-types), Duolang sheep and Chinese Merino. The results show that the differences of trace elements Fe, Cu, S were statistically significant (P<0.05)or very significan(tP<0.01), while the differences of Zn, Co were not statistically significant in different sheep breeds. Comparing variable with reference value, Fe was higher and Cu was lower and Zn, Co, S was normal in all breeds. For the different strains in Hetian sheep, in spite of they were living in different counties, the differences were not statistically significant(P>0.05). For the different flower-types in Karakul, the differences were also not statistically significant(P>0.05).To further this study, the content of 17 amino acids of wool in 4 breeds, including Hetian sheep (Pure plain Hetian, Pure mountain Hetian and New Hetian strains), Karakul sheep (Silkworm, girdle-type and rib-type three flower-types), Duolang sheep and Chinese Merino was determined by high performance liquid chromatography (HPLC). The aim is to search for the differences of amino acid content between the different breeds of sheep or the different strains of the same breed. The results show that the total amino acid content of wool from Hetian sheep is higher than that of Duolang sheep(P=0.016)and the difference is statistically significant(P<0.05). The differences in amino acid content are not statistically significant between the other breed(sP﹥0.05). Those amino acids in Duolang sheep such as Asp, Ser, Glu, Arg, Thr, Ala, Pro, Val, Lys, Ile, Leu, Phe are lower than that of the other breeds. The content of Cys in Karakul sheep is higher than that of the other breeds, but Ser, Gly, Thr, Pro, Tyr are lower than that of the other breeds. For the amino acids that promoteα-helix formation (Asp,Glu,Ala,Leu,Lys), the average content of Duolang sheep is lowest (4.82%) , Hetian sheep is highest (6.97%), Chinese Merino is 6.43% and Karakul sheep is 6.21%. For the amino acids that inhibitα-helix formation (Thr,Ser,Pro,Cys), the average amino acid content of Duolang sheep is lowest (6.45%) , Hetian sheep is highest (9.02%), Chinese Merino is 7.12% and Karakul sheep is 7.88%. So the ratio ofα-helix promoting/α-helix inhibiting amino acids in, Chinese Merino is 0.90, while in Karakul sheep it is 0.79, in Hetian sheep 0.77 and in Duolang sheep 0.75.