Exploiting RNA interference (RNAi) to modulate production traits and
develop disease resistance in poultry.
T.E.O’Neil1, T.J.Doran, S.G. Tyack, T.G.Wise, K.R.Morris, M.P.Bruce, M.M.Broadway,
R.J.Moore, D.M.Cummins, Y.Cao, S.C. Bannister, M.L.V. Tizard and J.W.Lowenthal.
1
Australian Animal Health Laboratory, CSIRO Livestock Industries, Australia.
RNA interference (RNAi) is a protective, innate cellular process used to induce sequence
specific knockdown of gene expression. The RNAi pathway involves the processing of
double stranded RNA (dsRNA) duplexes into 21-23 nucleotide molecules known as small
interfering RNAs (siRNA) to initiate gene suppression. RNAi can be mediated: exogenously
by synthetic oligonucleotides or vector-delivered double-stranded RNA; or endogenously by
microRNAs, leading to specific effects on gene expression. Exploiting the RNAi process may
enable better control over breeding strategies to modulate production and sex traits in poultry,
and provide alternative approaches for the control and prevention of important avian viral
diseases.
The economic and welfare benefits of producing single sex lines of poultry are widely
recognised. Modulating the sex ratio towards female only for egg production, or male only
for the broiler industry has universal appeal. The many benefits to the layer industry include:
increased productivity; provision of a welfare alternative to culling of non-laying male
chicks; and the adoption of innovative in ovo vaccine technology to control diseases that
impact on egg production. Conversely, the benefit to the chicken meat industry would be
higher feed conversion rates and growth in male only flocks. Sex determination in chickens is
chromosomally based, where males are homozygous (ZZ) and females are heterozygous
(ZW). It has recently been shown (Smith et al, Nature, 2009) that the Z-linked DMRT1 gene
is required for testis development in the chicken embryo and that knockdown of DMRT1
expression using virally delivered RNAi leads to the development of partial or complete
ovaries from the gonads of genetic males. Similarly, MIR202 has been shown to function in
regulating testicular development in chickens. These findings now provide a path to develop
an RNAi application to produce stably sex-reversed lines of poultry by manipulating the
activity of these key sex-determining genes during embryonic development.
A direct strategy to control viral infection in poultry is to employ RNAi to target specific
viral transcripts for the direct inhibition of the infectious process. RNAi has been effectively
used to inhibit the replication of avian influenza H5N1 virus in preliminary experiments in
chicken cells and embryonated eggs. These findings, in combination with improved methods
for genetically modifying chickens, provide us with the means and opportunity to genetically
engineer poultry to make them resistant to all strains of Avian Influenza (AI). The
development of an AI resistant transgenic chicken would have widespread benefits, not only
to the poultry industry, but to the greater population, as it would reduce the risk of a human
influenza pandemic by reducing the potential for virus re-assortment within intensively
reared birds.