cloning breakthrough

From: xgl (
Date: Thu Jun 29 2000 - 10:24:15 MDT

        wooo ... this was expected ... but then again, isn't everything?


---------- Forwarded message ----------
Date: Wed, 28 Jun 2000 15:00:15 PDT
From: "UPI / LIDIA WASOWICZ, UPI Science Writer" <>
Subject: Cloning method holds medical promise



        SAN FRANCISCO, June 28 (UPI) -- The scientists who produced
the world's first clone of an adult mammal, a sheep named Dolly, have
created two lambs using a method they say holds promise for a wide array
of medical benefits.
        The researchers at PPL Therapeutics in Edinburgh, Scotland,
reported in the British journal Nature the successful carrying out of
gene targeting in Cupid and Diana, named after the mythological figures
with legendary accuracy in hitting their target -- the aim of the refined
        The two lambs were cloned from sheep DNA -- the chemical
inside the cell nucleus that carries the genetic instructions for making
living organisms -- altered to contain specific changes, a technique
commonly used in mice but not previously effective in other mammals. Now
that it has been shown to work in an animal other than the mouse, gene
targeting could offer a way to introduce made-to-order genetic
alterations into many species, the researchers said.
        "Extension of gene targeting to other species could bring
considerable biological, medical and commercial benefits," lead study
author Alexander Kind told United Press International.
These could include:

        --Production of animal models better suited than the mouse for
shedding physiological light on human genetic diseases and testing
treatments for them.
        --Development of animals genetically modified to provide donor
organs for human transplantation.
        --Creation of animals that produce vast amounts of therapeutic
        --Generation of cattle that make "human milk," which could be
better tolerated than cow's milk by human infants.
        --Inactivation of prion genes to allow the study of so-called
prion diseases. The infectious agent prion has been linked to a group of
disorders that include Creutzfeldt-Jakob disease (CJD) and kuru in
humans, scrapie in sheep and bovine spongiform encephalopathy (BSE), also
called mad cow disease, in cattle.
        "This is an important breakthrough, which will undoubtedly
pave the way for the development and use of animal models of human
disease," Andrew Spicer, assistant professor in the Rowe Program in
Genetics in the Department of Biological Chemistry at the University of
California, Davis, School of Medicine, told UPI.
        "This is clearly a landmark paper, which will presumably be
followed by additional researchers demonstrating the applicability of
this approach to other species, particularly herd animals."
        "We are clearly at the dawn of a new era in mammalian genetic
technology", said Milind Suraokar and Allan Bradley of the Howard Hughes
Medical Institute in Houston, Texas, who wrote an accompanying News and
Views article.
        Scientists cautioned about ethical considerations in applying
the technology to humans but stressed that such application would be
covered by the strict guidelines currently in place to regulate human
        Gene targeting of mice has been common because the embryonic
stem cells -- the progenitor cells that give rise to all others -- in
mice are easy to change. Researchers can "knock out" -- or inactivate --
individual mice genes to recreate many human disorders. Not so in other
mammals, including sheep; modifying their stem cells is not effective.
        So Kind and colleagues came up with a way to achieve gene
targeting in sheep without the need for stem cells. In the technique
called nuclear transfer -- a similar version of which was used to create
Dolly in 1996 -- researchers first insert a DNA sequence into a specific
chromosome region of an adult sheep cell. Then they fuse these modified
cells with sheep eggs from which the nucleus has been removed. Sheep
grown from these eggs incorporate the targeted genetic change.
        "This is the key breakthrough.... that should make this
technology applicable to many species," Spicer said.
        "Our finding that stem cells are not necessary to achieve gene
targeting in animals is in my opinion the central point of our paper,"
Kind said. "The main block to progress in the area, the lack of embryonic
stem cells, has been removed, and I look forward to finding out how
generally applicable our methods prove to be."
        Gene targeting is a method of making precise, predetermined
modifications to an organism's genetic material. Scientists can add,
delete, replace or modify DNA sequences while leaving adjoining regions
unaltered -- an ability that has led to an explosion in the understanding
of gene function in mice, investigators said.
        The method employed by Kind and team is quite similar to that
carried out in mice -- with one critical difference: no embryonic stem
cells are needed.
        "Despite considerable efforts, no one has been able to derive
fully functional embryonic stem cells from animals other than mice," Kind
said. "Fully functional being defined as capable of contributing to all
cells of an animal, including the germ line (which would allow passage of
the trait to offspring). This has until now prevented the extension of
gene targeting to other species. Ours are the first gene targeted mammals
other than mice."
        The report comes on the heels of the announcement Monday that
two teams have decoded the genetic makeup of humans. Flanked by President
Clinton, with British Prime Minister Tony Blair appearing by video link,
Francis Collins, director of the Human Genome Project at the National
Institutes of Health, and J. Craig Venter, head of Celera Genomics, a
private company in Rockville, Md., reported the completion of a rough
draft of the human blueprint after 10 years of research.
        "This is the most important, most wondrous map ever produced
by humankind," Clinton said at the White House news conference.
        "Elucidation of the genome sequence and the identification of
each gene is the first step towards understanding how we develop, and
what causes things to go wrong, ultimately leading to disease," Spicer
told UPI. "The ability to investigate gene function in more than one
model species will allow us to more rapidly develop new strategies aimed
at disease prevention and treatment."
        The revolutionary technology of gene targeting, which has also
been used in plants, protozoans and microscopic worms, has spawned
visions of potential applications ranging from developing improved animal
models to study human disease and test potential therapies to providing
genetic treatment for those disorders.
        "One clear application of this technology is in the rapid
creation of specific herd animals in which a therapeutic protein is
expressed in the milk," Spicer said.
        "Using this technology, it may be more feasible to engineer
animals in order to provide transplant organs that survive substantially
longer in the transplant patient. Organs could be engineered such that
the major surface proteins recognized by the human immune system are
human, expressed by human genes that have been 'knocked into' the given
animal gene," Spicer said.
        "Another possible application of this technology is the
ultimate creation of cattle producing 'human milk.' By engineering the
cattle genes coding for the major milk proteins to modified versions that
express the human equivalents, it may be possible to create cattle that
produce milk that is much better tolerated by human infants. Formulas
more closely resembling human milk for instance."
        Improved animal models for human diseases could have a
significant impact, Spicer said.
        "Currently, the mouse represents the organism of choice for
modeling human genetic disease," he said. "This is primarily due to the
relative ease at which gene knockouts can be achieved in the mouse. For
many diseases, the mouse is not the ideal model, due to differences in
physiology, lifespan, etc. Ultimately, this breakthrough will provide
researchers with the ability to choose the model organism that may be the
most appropriate for the study of a particular disease."
        Over the past decade, advances in developing mice with
alterations to specific endogenous genes by gene targeting in embryonic
stem cells have been so rapid, scientists can now generate large numbers
of rodents with various gene deficiencies. These knockout mice provide
models for studying the function of individual mammalian genes and a
range of human inherited disorders, scientists said.
        For example, scientists found a defective homeotic, or Hox,
gene in mice creates effects similar to those seen in humans with Di
George syndrome. The mice with the mutated gene die at birth from
cardiovascular dysfunction caused by malformed heart vessels and muscle.
Di George syndrome is not brought about by a bad Hox gene in humans but
is thought to be caused by a gene that interferes with the HOX protein.
The mouse model can help scientists develop clues to treatment,
investigators said.
        Realizing the metabolic differences between man and mouse,
researchers have been working to design more sophisticated gene-targeting
methods to introduce subtle gene alterations.
        The technology has already benefited immunologists studying
the development of immune cells called lymphocytes and cancer researchers
analyzing the role of genes, such as the p53 suppresser gene, in tumors.
More than 80 percent of human cancers have been found to have a mutated
p53 gene.
        Scientists also expect gene targeting to have an impact on
neurobiology, providing a novel approach to cracking the molecular codes
that underlie learning, memory and other functions of the nervous system.
        First, some major challenges must be met, such as learning
which cell types are optimal for use in gene targeting.
        "In the mouse, gene targeting efficiencies are often
dramatically influenced by the use of 'isogenic' (from the same genetic
background as the embryonic stem cells being targeted) DNA in the
construction of targeting vectors," Spicer said. "If this is not as
important in other species, such as sheep, this would simplify the
        In their experiment, the researchers carefully chose the
target site for placing in Cupid a marker gene called neo and in Diana
the same marker plus a gene designed to produce a therapeutic protein
called alpha 1antitrypsin in her milk.
        "Targeting events were carried out to place genes adjacent to
a collagen gene," Kind said. "The significance of choosing this site was
to test whether it would support high expression of the transgene. Our
findings were that it did very well and may therefore provide a good
position for placement of other transgenes, rather than the 'lucky dip'
of random integration."
        PPL scientists have their current sights set on producing pigs
for xenotransplantation. In a first step toward that goal, researchers at
a PPL subsidiary in Blacksburg, Va., have produced the first cloned pigs.
The five little products of nuclear transfer -- named Millie, Christa,
Alexis, Carrel and Dotcom -- were delivered by Caesarean section March 5
at the Virginia-Maryland College of Veterinary Medicine.
        The birth was pronounced "a very significant accomplishment"
by PPL vice president of research Dave Ayares, who told a news
conference, "It has the potential to essentially revolutionize the
transplantation field."
     The Nature report can be viewed at <

Copyright 2000 by United Press International.
All rights reserved.

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