Keratin gene expression in Merino sheep with divergent wool growth
M. Bray A , D. K. Revell A , C. S. Bawden B and P. I. Hynd A CA Discipline of Animal Science, The University of Adelaide, Roseworthy Campus, Roseworthy, SA 5371, Australia.
B SARDI Livestock Systems, Roseworthy Campus, Roseworthy, SA 5371, Australia.
C Corresponding author. Email: philip.hynd@adelaide.edu.au
Australian Journal of Agricultural Research 56(3) 203-210 https://doi.org/10.1071/AR03253
Submitted: 3 December 2003 Accepted: 27 January 2004 Published: 23 March 2005
Abstract
South Australian Merino sheep were selected on the basis of high or low estimated breeding values (EBV) for wool growth rate (W), but with similar bodyweight, follicle density, and mean fibre diameter. Differences in the level of expression of keratin genes were examined in the skin of these sheep to test the hypothesis that divergence in EBV for wool growth is related to the production of wool proteins differing in sulfur (S) content. Further, it was proposed that this differential gene expression would be most pronounced when the supply of S amino acids to the animal was increased. Sheep selected for high EBV (+W) produced more wool per day than low EBV sheep (–W) (on average 32.5 v. 17.7 g/day clean wool, respectively; P < 0.05) but the S content of the wool did not differ between selection groups (2.77% v. 2.87% S, respectively; P = 0.2). Expression of keratin genes including keratin-associated protein KAP 2 (a high S gene), KAP 4 (an ultra-high S gene), KAP 6 (a high glycine/tyrosine gene), and the intermediate filament gene K 2.10, did not differ significantly between +W and –W groups. KAP 2 and K 2.10 each accounted for approximately 5% of the variation in wool growth rate (WGR) but expression of none of the genes examined was significantly related to the S content of the fibre produced. This suggests that differential keratin gene expression was not the source of genetic divergence in WGR. Instead the latter likely reflects a combination of differential cellular rate and growth processes (e.g. rate of bulb cell production, hypertrophy of cortical cells), differences in the relative production of inner root sheath and fibre from the follicle bulb cell population, or differential nutrient uptake into the follicle.
Additional keywords: follicle, sulfur.
Acknowledgments
The work was supported by the CRC for Premium Quality Wool. M. Bray was a recipient of an Australian Post-Graduate Award and a top-up scholarship from the CRC for Premium Quality Wool.
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