Transcript “Breeding systems and their genetic basis to improve quality and

“Breeding systems and their
genetic basis to improve quality
and production of animals”
Chris Moran
Professor of Animal Genetics and Animal
Biotechnology,
Centre for Advanced Technologies in Animal
Genetics and Reproduction,
Faculty of Veterinary Science
University of Sydney
HSC Agriculture Lectures 2005
Elective 2 – Animal Management
• discussing the impact or potential impact
of genetic engineering and associated
technologies on animal production
systems.
HSC Agriculture Lectures 2005
The target
• I will focus on one specific target for genetic
engineering to improve animal productivity
• This target relates specifically to ruminants,
such as sheep, cattle and goats
• I will then briefly list some other targets for
genetic engineering modifications
HSC Agriculture Lectures 2005
Limiting availability of sulphur
amino acids
• Proteins are synthesised from a set of 20 different
amino acids
• Dietary proteins are necessary for animal growth,
milk production and fibre production
• Essential amino acids are those which must be
acquired in the diet.
• The two sulphur amino acids, cysteine and
methionine, are the major dietary limiters to ruminant
growth and productivity
• Rumen micro-organisms break down dietary protein,
which may have plenty of cysteine and methionine,
and re-synthesise their own proteins, deficient in
these amino acids
HSC Agriculture Lectures 2005
How can genetic engineering help?
• Engineer the animal
• Engineer the plants
• Engineer the rumen micro-organisms
HSC Agriculture Lectures 2005
Modifying the animals
• Mammals have long lost the necessary
biosynthetic pathway for producing their
own cysteine from inorganic sulphur.
• Ruminants have abundant H2S in their gut
due to digestion of plant proteins by rumen
microbes
• Can we restore the lost ability to
synthesise this amino acid?
HSC Agriculture Lectures 2005
Cysteine biosynthetic pathway in bacteria
HSC Agriculture Lectures 2005
• A transgene has been constructed including both
these bacterial genes in tandem
• Controlled by a mammalian metallothionein
promoter, which directs expression to the small
intestine.
• Transgenic mice fed a cysteine deficient diet
supplemented only by Na2S had no signs of
cysteine deficiency, such as hair loss and loss of
body weight
• Introduced into sheep but not perfected
HSC Agriculture Lectures 2005
Modifying plants
• Some proteins escape rumenal digestion
and make it through to the small intestine
• Proteins can be chemically protected to
prevent rumen digestion
• Alternatively plants can be engineered to
produce proteins which escape rumenal
digestion and which have a good amino
acid balance
HSC Agriculture Lectures 2005
HSC Agriculture Lectures 2005
• The SFA8 gene has been transferred to peas
and lupins and other legumes
• Transgenic proteins have been produced at
levels of up to 2% of total seed protein.
• A level of 4% of SFA8 would increase sulphur
amino acids by 40%, which would have a
substantial impact on animal productivity.
• It has also been expressed in leaves – more
relevant for grazing animals
HSC Agriculture Lectures 2005
Modifying micro-organisms
• To produce an appropriate balance of essential
amino acids, including the sulphur amino acids
as well as threonine, isoleucine and leucine
• Genes encoding natural proteins- SFA8 and
casein have been introduced into rumen microorganisms to attempt to do this
• An artificial protein – MB1, enriched in the
essential amino acids, methionine, threonine,
lysine and leucine, which comprise 57% of the
protein, has been expressed at high levels in E.
coli
HSC Agriculture Lectures 2005
Other ways to influence animal
productivity and product value
• ANIMAL MODIFICATIONS
• Growth hormone transgenes – work well in
fish
• Anti-sense and siRNA protection against
pathogens, especially viruses
• Chitinase in skin to protect against fly
strike
• Adding nutraceuticals to milk eg lactoferrin
HSC Agriculture Lectures 2005
Other ways to influence animal
productivity and product value
• PLANTS
• Improving plant digestibility by reducing lignin
content – disrupting the lignin biosynthetic
pathway
• Edible vaccines – expressing viral and bacterial
antigens in plants to vaccinate animals orally –
much preliminary work in mice (E coli, Norwalk
virus, hepatitis B, mink enteritis virus)
• Passive immunisation –producing antibodies in
plants – plant antibodies have recognised target
molecules
HSC Agriculture Lectures 2005
Other ways to influence animal
productivity and product value
• Microbes
• Production of animal hormones eg bovine and
porcine somatotropin (growth hormone)
• Production of numerous vaccines eg Tickgard
• Modifying rumen microbes to better digest cellulose
• Modifying rumen microbes to detoxify chemicals in
diet eg introduction of dehalogenase to Prevotella
ruminicolla to detoxify fluoroacetate (1080) from
Acacia georginae
HSC Agriculture Lectures 2005
HSC Agriculture Lectures 2005
Conclusions
• Genetic engineering of animals, plants and
microbes has much to offer animal
production system
• The greatest impact on animal production
has been indirect
• There are still substantial social and
regulatory restrictions on genetic
engineering of animals for improved
productivity
HSC Agriculture Lectures 2005