Expression of FMRP by Neurosphere Derived Cells Following Transplantation in the Fragile X Mouse Model

Abstract

Fragile X Syndrome, characterized by intellectual impairment and learning disabilities is caused by a trinucleotide repeat expansion in the x-linked FMR1 gene leading to a complete lack of Fragile X Mental Retardation Protein (FMRP). Neural stem/progenitor cells (NSCs) cultured as floating aggregates of cells commonly referred to as neurospheres can survive, differentiate and integrate into the host environment when transplanted to the rodent CNS. Neurospheres were established from early postnatal wild-type mice and labeled with the cytoplasmic dye CFDA-SE and then stereotaxically injected as cell suspensions into the hippocampus of young adult (3-6 week old) FMR1 knockout mice. Immunocytochemical analysis of the brains revealed the presence of FMRP-expressing cells up to two weeks after transplantation. Some transplanted cells migrated within the host hippocampus and formed dendrite-like processes. A small subpopulation of the transplanted cells expressed markers of neuronal or glial phenotypes, although many cells did not stain for any of the markers that we probed. These experiments constitute an attempt to restore FMRP-expression in the brains of FMR1 knockout mice using cell suspension transplants of stem and progenitor cells.