First use of DNA fingerprinting to identify viable embryos
Research could lead to improved pregnancy rates and fewer multiple
pregnancies
Fertility researchers have used DNA fingerprinting for the first time
to identify which embryos have implanted after in vitro fertilisation
(IVF) and developed successfully to result in the births of healthy
babies. The technique, combined with sampling cells from blastocysts
(the very early embryo) before implantation in the womb, opens the
way to pin-pointing a handful of genes that could be used to identify
those blastocysts most likely to result in a successful pregnancy.
The authors of the research [1], published online in Europe's leading
reproductive medicine journal, Human Reproduction, today (Wednesday
14 May), believe that their findings will revolutionise IVF by
improving pregnancy rates and eliminating multiple pregnancies.
When couples attend fertility clinics for IVF, eggs from the woman
are fertilised with sperm from the man and then the fertilised eggs
are allowed to develop in the laboratory until they reach the
blastocyst stage after about five days [2]. Before the blastocysts
are implanted into the woman's womb, a decision has to be made about
how many should be implanted and which ones look most likely to
develop successfully. Currently there is no reliable way of
differentiating between viable and non-viable blastocysts, and clinic
staff tend to decide on the basis of some fairly crude tests, which
include looking at the form (morphology) of the blastocyst. The
result is that couples often opt to have more than one blastocyst
implanted in order to increase their chances of a successful
pregnancy; but this runs the risk of multiple pregnancies with all
the associated dangers to both the mothers and babies.
When multiple embryos are transferred, it then becomes impossible to
work out which are the ones that developed into a successful
pregnancy, making it difficult to develop criteria for identifying
viable blastocysts.
One of the authors of the paper, Dr David Cram, senior research
scientist at the Monash Immunology and Stem Cell Laboratories, Monash
University, Australia, said: "DNA fingerprinting is the ultimate form
of biological identification, but until now it has not been used to
identify the embryonic origin of resultant babies born following
embryo transfer; nor has it been used for gene expression studies. We
have developed a novel strategy of utilising a combination of
blastocyst biopsy, DNA fingerprinting and microarray analysis to
identify viable blastocysts among the cohorts transferred to
patients. Our ultimate aim is to find out which genes are expressed
by viable blastocysts.
The researchers from Monash University and Dr Kostas Pantos and Ms
Georgia Kokkali from the Centre for Human Reproduction, Genesis
Athens Hospital, Athens, Greece, recruited 48 women undergoing in
vitro fertilisation treatment, and after eggs were fertilised and
developed in culture for five days, removed between eight and 20
cells from the trophectoderm cell layer of the resulting blastocysts.
These samples were amplified and their gene expression analysed using
microarrays (a method of using genetic probes on a microchip to
target sequences of messenger RNA [3]). One or more blastocysts were
transferred to all 48 women and 25 became pregnant, with 37 babies
being born. In seven women all the blastocysts implanted, in 18 women
some implanted and some did not, which indicated that there was not a
problem with the uterus, and in 23 women none of the blastocysts
implanted, which indicated that either all the blastocysts were non-
viable or that the uterus was not receptive.
When the babies were born, blood from the umbilical cord or swabs of
cheek cells were taken and stored. The researchers used DNA
fingerprinting on these samples to match them with the DNA obtained
from the blastocyst biopsies, thereby identifying which embryo grew
into which baby. Then they used microarray to analyse the genetic
message and find out which genes were expressed in the viable
blastocysts. This work is still continuing, but already they have
discovered that genes known to be involved cell adhesion, cell
communication, cellular metabolic processes and response to stimuli –
key processes involved in embryo implantation – are expressed in the
viable blastocysts.
Dr Gayle Jones, a co-author and senior research scientist at the
Monash Immunology and Stem Cell Laboratories, said: "We believe that
it will be possible to refine our gene set to a smaller number of
genes that is more highly predictive of a blastocyst's viability and
ability to develop to a term pregnancy when transferred to a
receptive uterus than current selection criteria. The ability to
select the single most viable embryo from within a cohort available
for transfer will revolutionise the practice of IVF, not only
improving pregnancy rates but eliminating multiple pregnancies and
the attendant complications.
The most important new findings from the research are:
that up to 20 trophectoderm cells can be removed from a blastocyst
without adversely affecting its viability and ability to implant;
DNA fingerprinting is a very useful technique for discriminating
between viable and non-viable blastocysts;
trophectoderm cells from viable and non-viable blastocysts have
different patterns of gene expression, which, when refined, could be
used to select the single most viable embryo from a group for
transfer.
Although more work needs to be undertaken before these findings
become applicable in the clinic, the researchers say that their work
will also be useful for testing different treatments of embryos
without the need to recruit large numbers of women to clinical
trials, and DNA fingerprinting could be used to refine existing
criteria for selecting embryos for implantation.
Dr Jones said; "Major improvements in IVF practice in the last decade
have seen the introduction of better laboratory techniques that allow
complete pre-implantation development to the blastocyst stage in
vitro. One of the major stumbling blocks to worldwide acceptance of a
single embryo transfer policy is the lack of highly predictive
criteria to select the single most viable embryo within a cohort. The
ability to use objective, measurable criteria rather than subjective
observations, such as morphology, should improve the predictive value
and provide sufficient confidence for clinicians to shift towards
single embryo transfers for all patients without a concomitant drop
in pregnancy rates. This would effectively reduce multiple
pregnancies, which is a priority in the field of assisted
reproductive medicine at present."
###
[1] Novel strategy with potential to identify developmentally
competent IVF blastocysts. Human Reproduction. Published online under
advance access. doi:10.1093/
[2] The blastocyst is the stage at which the embryonic cells have
started to differentiate into the different cell layers that will go
on to form the foetus or the placenta.
[3] Messenger RNA (or mRNA) is a key intermediary in gene expression,
translating the DNA's genetic code into the amino acids that make up
proteins.
Public release date: 13-May-2008
Contact: Emma Mason
wordmason@mac.
07-711-296-986
European Society for Human Reproduction and Embryology
http://www.eurekale
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
StemCells subscribers may also be interested in these sites:
Children's Neurobiological Solutions
http://www.CNSfoundation.org/
Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123
The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
____________________________________________
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
__,_._,___
No comments:
Post a Comment