Functional genomics approach to identifying peripheral markers for sheep scrapie
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Date
25/11/2009Author
Roupaka, Sofia
Metadata
Abstract
Scrapie is a transmissible spongiform encephalopathy (TSE) of sheep and goats, for
which there is currently no ante-mortem diagnostic test. A rapid, ante-mortem
diagnostic test for scrapie would also potentially be important for other TSEs such as
bovine spongiform encephalopathy (BSE) and variant Creutzfeldt Jakob’s disease
(vCJD).
The hypothesis of this study was that there is differential gene expression in the
blood and peripheral tissues of scrapie infected animals, and that a panel of
differentially expressed genes could be identified and used as surrogate markers of
infection.
An expression screening approach, using real-time PCR and an EST microarray, was
used to identify genes that were differentially expressed between SSBP/1 infected
and mock-infected control sheep. The animals used in this study were New Zealand
Cheviot sheep of three genotypes, the highly susceptible VRQ/VRQ (incubation time
193 ± 12 days), the intermediately susceptible VRQ/ARR (incubation time 325 ± 36
days) and the disease resistant ARR/ARR (no clinical signs of disease),
experimentally infected with scrapie strain SSBP/1 and sacrificed at various time
points post infection. No differentially expressed candidates were identified in blood.
Other microarray experiments in our group had demonstrated evidence of differential
expression in spleen fractions enriched for follicular dendritic cells (FDCs). These
data were analysed and candidates were selected for quantitative real-time PCR
validation, with a view to assessing the expression of validated candidates in blood
as a more targeted approach to identifying markers of infection. The gene Early
Growth Response 1 (EGR1) emerged as an interesting candidate as its expression
was found to be significantly up-regulated in FDC-enriched spleen samples of
VRQ/VRQ and ARR/ARR animals over a number of time points post infection.
EGR1 expression was steady among all mock-infected controls. There was, however,
no evidence of differential expression of EGR1 in blood.
This is the first report of differential expression of EGR1 in preclinical spleen
samples in sheep. EGR1 is an attractive candidate for a surrogate marker of
preclinical infection, as its levels rise very early after infection and remain elevated
for a sustained amount of time in the VRQ/VRQ sheep. Elevated expression is also
detectable in VRQ/ARR and in ARR/ARR sheep. Further studies with larger sample
numbers would be necessary to more accurately estimate the extent of differential
expression and to assess its true worth as a diagnostic marker. Expression studies in
samples from other TSEs and non-TSE neuropathological disease would also be
necessary to establish whether differential expression of EGR1 is specific to TSE
disease.