Knockdown and Overexpression of FMR4 in HEK293T cells at 6 and 24 hours

CGG repeat expansions in the Fragile X mental retardation 1 (FMR1) gene are responsible for a family of associated disorders characterized by either intellectual disability and autism (Fragile X Syndrome, FXS), or adult-onset neurodegeneration (Fragile X-associated Tremor/Ataxia Syndrome, FXTAS). However, the FMR1 locus is complex and encodes several long noncoding RNAs (lncRNAs), whose expression is altered by repeat expansion mutations. The role of these lncRNAs is thus far unknown; therefore we investigated the functionality of FMR4, which we previously identified. Full-length expansions of the FMR1 triplet repeat cause silencing of both FMR1 and FMR4, thus we are interested in potential loss-of-function that may add to phenotypic manifestation of FXS. Since the two transcripts do not exhibit cis-regulation of one another, we examined the potential for FMR4 to regulate target genes at distal genomic loci using gene expression microarrays. We identified FMR4-responsive genes, and further investigated their function related to human neural precursor cells. We therefore propose that FMR4s function is as a gene-regulatory lncRNA and that this transcript may function in normal development. Closer examination of FMR4 increases our understanding of the role of regulatory lncRNA and the consequences of FMR1 repeat expansions.

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