Femke de Vrij, Rob Willemsen

Rob Willemsen, PhD, Principal Investigator
Femke de Vrij, PhD, Postdoctoral Fellow
Erasmus University Rotterdam
The Netherlands

FRAXA Awards:
  $50,000 in 2007
  $50,000 in 2006

update by Rob Willemsen, 4/2007

Goals of this project include making a transgenic mouse strain with an inducible fluorescent fmr1 fusion gene in an fmr1 knockout background. This mouse model will be used for culturing primary neurons or long term organotypic brain slice cultures in which the fmr1 gene can be switched on by the addition of doxycycline to the medium to achieve tightly regulated FMRP expression. Expression of FMRP can be seen easily, since green fluorescent protein will be produced wherever FMRP is produced.

We will also generate and characterize a transgenic mouse strain with an inducible (TET-off) EGFP-AMPA(GluR-A) receptor fusion gene in an fmr1/GluR-A (double)knockout background. This mouse model will be applied to study the role of FMRP in AMPA (GluR-A) receptor surface expression in both primary neurons and long-term organotypical cultures of brain slices. This will allow study of an important corollary of the "mGluR Theory of Fragile X", since excessive mGluR signaling is thought to cause a significant decrease in AMPA receptor expression in fragile X.

Further goals include characterization of a transgenic mouse strain with an EGFP-tKRAS fusion gene in both WT and Fmr1 knockout background. This mouse model will be used to study high-resolution images of spine morphology using both primary neurons and long-term organotypical cultures of brain slices.

by Rob Willemsen, 3/2006

Absence of FMR1 protein (FMRP) in neurons of both fragile X patients and Fmr1 knockout mice causes functional and morphological changes of spines. Compelling evidence shows that FMRP plays a role in (repressive) translational control of specific dendritic mRNAs. Lack of FMRP in neurons may lead to uncontrolled protein synthesis at the synapse upon mGluR stimulation. Reducing mGluR activation may (partly) reverse the effects due to the lack of FMRP. MPEP, an antagonist that specifically blocks mGluR5, is successfully employed in fragile X research to rescue some phenotypic features in Fmr1 knockout mice.

As a first step in treatment of fragile X patients, these drugs need to be further tested in mouse models using behavioral and functional studies. In addition, future pre-clinical studies should also include research studies aimed at understanding the underlying molecular mechanisms of therapeutic approaches.

The aim of this project is to generate and characterize specific mouse models that will enable us to study the role of FMRP in dendritic mRNA transport, translation of target mRNAs at the synapse and the molecular mechanisms underlying (novel) therapeutic intervention using mGluR antagonists. The role of FMRP in transport/translation of dendritic mRNAs will be studied in cell cultures from primary neurons in which the FMR1 gene can be switched on/off by adding drugs to the cell culture medium. The FMR1 gene is fused to a fluorescent dye to follow the fluorescent fusion-protein during transport to the synapse. Abnormalities of spines will be studied in a mouse strain that express a fluorescent plasma membrane marker. In addition, these mice can be applied to visualize the reverse of abnormal spines in rescue studies, including MPEP treatment. Finally, a mouse strain which express fluorescent AMPA receptors will be used to study AMPA receptor surface expression after mGluR stimulation in the absence/presence of mGluR antagonists, including MPEP.