O o d h e a d p u b L i s h I n g L i m I t e d

partial adoption. The technique (Bioclip™) requires special equipment for
harvesting the wool and is not applicable to sheep weight over 60 kg or to
pregnant ewes. There may be other growth factors known and unknown that
might be found to act more effectively than EGF in temporarily disrupting
wool growth, but discovering such factors would require extensive basic and
applied research. There may be a factor or factors that could be used in
conjunction with EGF to improve its efficacy and application. Researchers
in transgenic sheep technology have considered the possibility of making
sheep transgenic to EGF and controlling its expression in the skin when
needed but it is not conceivable that such a procedure with so many complex
issues associated with it could replace the direct simple injection of EGF.
Nevertheless ‘gene discovery’ research for example, into the normal follicle
mechanisms in Wiltshire sheep that bring about seasonal shedding (Nixon
et al., 2002) could bring forth new information that might be utilised in
developing new molecular methods for the harvesting of wool.
External parasite infestation such as blowfly strike is another problem.
Attention has been focused on the possibility of controlling it by secreting
insecticidal proteins into the follicle areas around the breech of the sheep.
Known insecticidal proteins that could be candidates for investigation through
sheep transgenesis are wheat agglutinin (Giovanini et al., 2007) and proteins
from
 
Bacillus thuringiensis (Carlini and Grossi-de-Sa, 2002). A strategy for
targeting such molecules to make them secrete onto the skin of the sheep
could be to link the insecticide gene to a gene promoter of a gene from the
sebaceous or sweat glands. Strategies of this kind were initiated by CSIRO
within the CRC for Premium Quality Wool but ceased on closure of the
CRC.
Molecular methods to control the problem of dark fibres in wool would
appear to have some potential since the genetics, biochemistry and cellular
mechanisms of melanin formation are understood and coat colour has been
induced by expression of the tyrosinase gene in transgenic mice (Lavado
et al., 2005; Tanaka and Takeuchi, 1992). Studies to reduce the expression of
© 2009 Woodhead Publishing Limited

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Improvement of wool production through genetic manipulation
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the tyrosinase gene in the melanin pathway by utilising anti-sense mRNAs
were initiated by CSIRO during the life of the CRC for Premium Quality
Wool. Since that time the discovery of microRNAs that are normally used by
cells to regulate genes (Scherr and Eder, 2007) provides more tools for
investigating the dark fibre problem.