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Absence of critical protein linked to infertility
Jim Barlow,
Life Sciences Editor
217-333-5802; jebarlow@uiuc.edu
1/17/2006
|
CHAMPAIGN, Ill.
— The absence of a key protein may lead to infertility.
Researchers at the University of Illinois at Urbana-Champaign report
that experiments involving mice – to be detailed in the Proceedings
of the National Academy of Sciences – indicate that the transcription
factor protein C/EBPb must be present in the uterus for pregnancy to
occur. The study appears online this week at the PNAS Web site.
Without it, they say, an embryo cannot survive in uterine tissue or
attach to a mother’s blood supply. Other genes also play roles,
but C/EBPb is critical for implantation of an embryo, said Milan K.
Bagchi, a professor of molecular
and integrative physiology.
C/EBPb is scientifically known as CCAAT/Enhancer Binding Protein beta.
It is regulated by the hormones estrogen and progesterone. In normal
conditions, the protein, driven mostly by progesterone, is expressed
rapidly and in large quantities during the critical four-day implantation
period in mice, Bagchi said.
During this period, an embryo attaches to the wall of the uterus, advances
into it and eventually attaches to the blood supply and forms the placenta.
For a successful pregnancy to occur, stromal cells of the uterus must
be transformed into decidual cells, which secrete nutrients that allow
the embryo to survive until it plugs into the blood supply. C/EBPb is
necessary for decidualization, the researchers discovered.
“This protein in the mouse is also in humans,” Bagchi said.
“We believe it plays a critical role in human pregnancy. It is
expressed in the human endometrium at a time that coincides with the
time of implantation. We have demonstrated very clearly in the mouse
that in the absence of C/EBPb there is no decidualization. We transferred
viable mouse embryos from healthy mice into mice lacking the gene, and
pregnancy failed.”
The project began more than four years ago.
First, researchers used DNA microarrays to identify gene expression
under normal and abnormal conditions during implantation. After messenger
RNA profiling zeroed in on C/EBPb’s activity, the researchers
collaborated with Peter F. Johnson of the National Cancer Institute’s
Laboratory of Protein Dynamics and Signaling, who created mice that
lacked the protein.
The experimental mice were then used to observe the relationships of
the hormones and their receptors with the protein under varying conditions
during the critical implantation period. In doing so, researchers determined
that C/EBPb is a critical mediator of steroid hormone responsiveness
in the uterus.
"This gene is expressed when the uterus is ready for embryo attachment,”
said co-author Indrani C. Bagchi, a professor of veterinary
biosciences in the U. of I. College
of Veterinary Medicine. “Its presence indicates a window for
success.”
If the findings are replicated in human tissue, as expected, she said,
the protein’s presence could become a vital gene marker for predicting
uterine readiness for pregnancy.
“The success rate for the practice of in vitro fertilization currently
is, on average, about 25 percent,” she said. “The major
problem is that the conditions occurring when the embryo is transferred
often are not the best in the uterus. It’s not known if the uterus
is ready to accept an embryo, so often multiple embryos are transferred
in hopes that one will attach. In future studies, confirmation of C/EBPb
as a marker that correctly indicates uterine readiness for implantation
in the human is likely to alleviate these shortcomings.”
Other co-authors of the paper were doctoral student Srinivasa Raju Mantena,
postdoctoral researchers Athilakshmi Kannan and Yong-Pil Cheon, and
research scientist Quanxi Li, all in Indrani Bagchi’s veterinary
biosciences laboratory.
The National Institutes of Health funded the research.
