Stephen T. Warren, PhD
Principal Investigator

Shuang Chang, PhD
Postdoctoral Fellow

Department of Human Genetics
Emory University School of Medicine




FRAXA Awards:
  $40,000 in 2006
  $40,000 in 2005
  $40,000 in 2004
  $35,000 in 2000

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.

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.