Rachel Smith is a graduate of the University of Western Australia, with a First Class Honours degree. She commenced studies towards her PhD in 1995 having been awarded an IWS scholarship. The Wool CRC contributed financially towards the final six months of Rachel’s work. Rachel was supervised by Dr Janelle Hocking Edwards of the Education Program and the Department of Animal Science at UWA. The following is a brief summary of her research project.
“Much of the research into nutrition and wool growth has centred on the supply and utilisation of amino acids by the follicle, but very little research has examined the means by which follicles obtain and use energy substrates. My work is the first to look at energy metabolism in detail in wool follicles.”
The first experiment I conducted was aimed at determining whether or not the glycogen levels in wool follicles are altered by nutrition, and whether glycogen content is related to wool growth rate. To examine this, I placed groups of sheep on restricted plans of nutrition and then allowed them to rapidly gain weight. The restricted nutrition groups lost approximately 20% of their original liveweight over the 12 weeks of declining nutrition and rapidly regained weight during the six-week recovery period. Wool production, fibre diameter, staple length growth rate, muscle glycogen concentration and follicle bulb division rate all reflected the pattern of liveweight loss. Skin glycogen concentration was responsive to nutrition and there was a strong correlation between skin glycogen concentration and wool production.
In this experiment I experienced problems in measuring glycogen levels in biopsied skin tissue. The variation in glycogen concentration between sample times exhibited a regular pattern, most likely an artifact of sampling rather than a biological phenomenon. There are two factors that may have contributed to the weekly variation in glycogen concentration evident in Experiment 1:
After a good deal of experimentation, I tracked the problem down to poor repeatability of extraction of the glycogen from the biopsy tissue, and found that a potassium hydroxide extraction method worked well.
It was established during Experiment 1 that the skin glycogen concentration responds to nutritional manipulation. The objectives of the next experiment were to examine the dynamics of skin glycogen in genetically high and low staple strength animals and to demonstrate that glucose transporter type 1 (GLUT1) expression changes in parallel to glycogen dynamics in ovine skin. The nutritional simulation of feed availability at the break of season was repeated in this experiment. Liveweight, wool production, fibre diameter, staple length growth rate and staple strength demonstrated similar trends to Experiment 1. These parameters were significantly affected by nutrition, but not by genetic staple strength line.
Another experiment was then conducted to localise GLUT1 protein distribution and to examine expression of GLUT1 in ovine skin in response to a short-term oral glucose load. The hypothesis was that an oral glucose load will up-regulate GLUT1 expression in the wool follicle. The experiment was conducted for five days. Four treatments were used to test the hypothesis:
Glycogen content of the skin did not differ significantly between treatments. I have had no success in detecting GLUT1 protein in sheep skin using an immunological approach, due to problems with the antibody. We have decided to switch to a molecular approach to detect Glut-1 mRNA.”
The final set of experiments investigated the medium and short-term manipulation of glycogen in the skin. Glucose was infused intravenously in an attempt to increase the amount of glycogen stored in the skin. These experiments will be finalised in the near future.
In November 1998 Rachel attended the Second Intercontinental Meeting of Hair Research Societies (at Washington DC, USA,) and presented a poster entitled, ‘Glycogen depletion in ovine skin’. At the Second National Scientific Meeting of the Australasian Hair and Wool Research Society in Perth, May 1999, Rachel presented her results.
In this issue of The Wool Press: