Stephen T. Warren, PhD
Principal Investigator
Joshua Suhl, PhD, Postdoctoral Fellow (2009)
Shuang Chang, PhD, Postdoctoral Fellow (2006)
Department of Human Genetics
Emory University School of Medicine
This team is developing a new model for studying fragile X: induced pluripotent stem cells are stem cells that can be derived from any cell (fibroblasts from skin samples or mouth swabs, for example). This technology will enable scientists to derive cells from many different individuals with fragile X, to be converted into stem cells which can form long-lived cultures. Giving the enormous variety in fragile X symptoms, this is an exciting advance.
by Joshua Suhl and Stephen T. Warren, updated 3/31/10
We are developing induced pluripotent stem (iPS) cells to serve as a stem cell model and screening tool for potential treatments of Fragile X. This new technology “reprograms” adult cells (for example, skin cells) to stem cells, which are similar to human embryonic stem cells (hESCs), can be cultured indefinitely, and provide a virtually limitless source of Fragile X cells for research purposes. hESCs that contain the CGG repeat expansion have been shown to express FMR1. At some point after stem cell differentiation into other cell types, the gene is silenced. iPS cells will provide a pre-differentiation cellular model, permitting research into the timing and mechanism of the FMR1 silencing event.
Additionally, our team has recently identified several novel mutations in the FMR1 gene from a group of developmentally delayed males that may affect the function of FMRP. Several of these variants will be analyzed to determine if any can be identified as a new cause of Fragile X, highlighting the possibility of alternative etiologies other than the typical repeat expansion and opening new avenues of Fragile X research.
by Shuang Chang and Stephen T. Warren, 3/2006
We have discovered that Drosophila embryos deficient in dfmr1, the fly model of fragile X syndrome,
die when placed on a commercial food source but survive on a standard laboratory food preparation.
The commercial food source was found to contain excess glutamate when compared to the lab food and
adding glutamate to the lab food resulted in lethality. The mGluR antagonist MPEP rescued the lethality
on commercial food, consistent with the mGluR theory of fragile X syndrome.
Using this lethal phenotype
on commercial food as a drug screen, we evaluated a panel of 2,000 drugs and natural products, identifying
compounds that could rescue the phenotype. This screen identified 20 drugs that could rescue the phenotype
and further replication showed four lead drugs to be superior to MPEP in reversing the lethality. Those flies
that survived with drug treatment also showed significantly correction the morphological brain abnormality
(mushroom body lobe defects) seen in dfmr1-deficient flies growing on lab food. Three of these four drugs
appear to modulate the GABAergic inhibitory pathway. Since this inhibitory pathway could temper the excess
signaling from the mGluR excitatory pathway in fragile X, we have identified the GABAergic pathway as a
druggable target for fragile X syndrome. We are planning expanding the drug-screening panel and testing
these four lead drugs in mice deficient in Fmr1.
Usha Narayan, PhD
Postdoctoral Fellow
Funded January 2005 ($40,000)
by Usha Narayan and Stephen T. Warren, 8/06
Previous work has shown that FMRP is an RNA binding protein that specifically recognizes target mRNA
transcripts and influences their translation status. Although FMRP is known to be synthesized/ transported in
response to group 1 mGluR activity, little is known about its role in translation in a similar context.
Post-translational modifications (such as phosphorylation) are good candidates for the regulation of
activity-dependent protein synthesis. We recently identified protein phosphatase 2A (PP2A) as a major
FMRP phosphatase in both primary neurons and non-neuronal cells. Alterations in PP2A activity were found
to mediate rapid and dynamic changes in FMRP phosphorylation upon group 1 mGluR stimulation in primary
hippocampal neurons. This mGluR activity-dependent FMRP phosphorylation also correlates with the translational
changes of dendrite-localized target transcripts.
Together, these data link group 1 mGluR activation, PP2A
enzymatic activity and FMRP phosphorylation with downstream translation. Current efforts are directed at
investigating the therapeutic potential of this novel signaling cascade.
Reid Alisch, PhD
Postdoctoral Fellow
Funded in July 2004 ($40,000)
by Michael Tranfaglia MD, FRAXA Medical Director
This group will use novel strategies to
examine the binding activity of FMR1
protein, to see which target mRNAs it
associates with and presumably regulates.
They will also investigate the RNA targets
of two similar proteins, FXR1 and FXR2,
which are thought to work with FMRP in most, if not all, of
its functions. They also plan to look at the different binding
patterns of different isoforms of FMRP; one important fact
which is seldom discussed is that FMRP can exist in cells in
at least 12 distinct forms, depending on how it is spliced
by various cells. It is entirely possible that each of these
forms has somewhat different characteristics, which need to
be better understood. Furthermore, the investigators hope
that by comparing FMRP from different species, such as
chicken and frog, they can learn more about which parts of
the Fragile X protein perform specific functions (such as
binding RNA, engaging transport mechanisms, etc.)
This is an important area of research because greater
understanding of FMRP’s targets will enable us to identify
other genes and other proteins which may be causing the
pathology in Fragile X. These may, in turn, be potential
targets for drug development.
