Gene-edited livestock 'surrogate sires' successfully made fertile
Advance could transform selective animal breeding

Date:
September 14, 2020
Source:
Washington State University
Summary:
For the first time, scientists have created pigs, goats
and cattle that can serve as viable 'surrogate sires,' male
animals that produce sperm carrying only the genetic traits of
donor animals. The advance could speed the spread of desirable
characteristics in livestock and improve food production for a
growing global population.



FULL STORY ==========================================================================
For the first time, scientists have created pigs, goats and cattle that
can serve as viable "surrogate sires," male animals that produce sperm
carrying only the genetic traits of donor animals.


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The advance, published in the Proceedings of the National Academy of
Sciences on Sept. 14, could speed the spread of desirable characteristics
in livestock and improve food production for a growing global
population. It also would enable breeders in remote regions better
access to genetic material of elite animals from other parts of the
world and allow more precision breeding in animals such as goats where
using artificial insemination is difficult.

"With this technology, we can get better dissemination of desirable traits
and improve the efficiency of food production. This can have a major
impact on addressing food insecurity around the world," said Jon Oatley,
a reproductive biologist with WSU's College of Veterinary Medicine. "If
we can tackle this genetically, then that means less water, less feed
and fewer antibiotics we have to put into the animals." A research
team led by Oatley used the gene-editing tool, CRISPR-Cas9, to knock
out a gene specific to male fertility in the animal embryos that would
be raised to become surrogate sires. The male animals were then born
sterile but began producing sperm after researchers transplanted stem
cells from donor animals into their testes. The sperm the surrogate sires produced held only the genetic material of the selected donor animals. The gene-editing process employed in this study seeks to bring about changes
within an animal species that could occur naturally, such as infertility.

The study is the result of six years of collaborative work among
researchers at WSU, Utah State University, University of Maryland and
the Roslin Institute at the University of Edinburgh in the U.K.

The researchers used CRISPR-Cas9 to produce mice, pigs, goats and cattle
that lacked a gene called NANOS2 which is specific to male fertility. The
male animals grew up sterile but otherwise healthy, so when they received transplanted sperm-producing stem cells from other animals, they started producing sperm derived from the donor's cells.



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The surrogate sires were confirmed to have active donor sperm. The
surrogate mice fathered healthy offspring who carried the genes of the
donor mice. The larger animals have not been bred yet. Oatley's lab
is refining the stem cell transplantation process before taking that
next step.

This study provides a powerful proof of concept, said Professor Bruce
Whitelaw of the Roslin Institute.

"This shows the world that this technology is real. It can be used,"
said Whitelaw. "We now have to go in and work out how best to use it productively to help feed our growing population." Latest step in animal husbandry Scientists have been searching for a way to create surrogate
sires for decades to overcome the limitations of selective breeding and artificial insemination, tools which require either animal proximity or
strict control of their movement -- and in many cases, both.



========================================================================== Artificial insemination is common in dairy cattle who are often confined
so their reproductive behavior is relatively easy to control, but the
procedure is rarely used with beef cattle who need to roam freely to
feed. For pigs, the procedure still requires the animals be nearby as pig
sperm does not survive freezing well. In goats, artificial insemination
is quite challenging and could require a surgical procedure.

The surrogate sire technology could solve those problems since the
surrogates deliver the donor genetic material the natural way -- through
normal reproduction. This enables ranchers and herders to let their
animals interact normally on the range or field. Donors and surrogates
do not need to be near each other since either frozen donor sperm or the surrogate animal itself can be shipped to different places. In addition,
female NANOS2 knockout animals remain fertile -- since the gene only
affects male fertility -- and could be bred to efficiently generate
sterile males to be used as surrogate sires.

This technology has great potential to help food supply in places in
the developing world, where herders still have to rely on selective
breeding to improve their stock, said Irina Polejaeva, a professor at
Utah State University.

"Goats are the number one source of protein in a lot of developing
countries," Polejaeva said. "This technology could allow faster
dissemination of specific traits in goats, whether it's disease
resistance, greater heat tolerance or better meat quality." The surrogate sires technology could also open up a new option for genetic conservation
of endangered species, whose dwindling numbers leave animal communities isolated from each other, limiting their genetic diversity.

Perception and policy hurdles None of the benefits of surrogate sires
can be realized, however, without changes in the current landscape of government regulations and public perception.

Even when the technology is advanced enough for commercialization,
gene-edited surrogate sires could not be used in the food chain anywhere
in the world under current regulations, even though their offspring
would not be gene-edited. This is due in part to the misperceptions
that gene editing is the same as the controversial gene manipulation,
Oatley said. Gene editing involves making changes within a species that
could occur naturally. It does not combine DNA from different species.

Oatley realizes there is a lot of work to do outside of the lab and
recently joined the National Task Force on Gene Editing in Livestock to
bring together researchers, industry representatives, bioethicists and policymakers to find a path forward for the technology.

"Even if all science is finished, the speed at which this can be put
into action in livestock production anywhere in the world is going
to be influenced by societal acceptance and federal policy," said
Oatley. "By working with policymakers and the public, we can help to
provide information assuring the public that this science does not
carry the risks that other methods do." This study was supported by
the USDA National Institute of Food and Agriculture, WSU's Functional
Genomics Initiative and Genus plc. The Roslin Institute receives strategic investment funding from the Biotechnology and Biological Sciences Research Council, as part of U.K. Research and Innovation, and it is part of the University of Edinburgh's Royal (Dick) School of Veterinary Studies. At
Utah State University, this study was supported by the Utah Agricultural Experiment Station.


========================================================================== Story Source: Materials provided by Washington_State_University. Original written by Sara Zaske. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Michela Ciccarelli, Mariana I. Giassetti, Deqiang Miao, Melissa J.

Oatley, Colton Robbins, Blanca Lopez-Biladeau, Muhammad Salman
Waqas, Ahmed Tibary, Bruce Whitelaw, Simon Lillico, Chi-Hun Park,
Ki-Eun Park, Bhanu Telugu, Zhiqiang Fan, Ying Liu, Misha Regouski,
Irina A. Polejaeva, and Jon M. Oatley. Donor-derived spermatogenesis
following stem cell transplantation in sterile NANOS2 knockout
males. PNAS, 2020 DOI: 10.1073/pnas2010102117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200914160748.htm

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