FMRP, the protein missing in fragile X syndrome, is proving to be one of the brain's best multitaskers: it's needed for the birth of new neurons, to regulate protein translation, and for maintaining the structural integrity of spiny neuronal projections, according to several new studies.Scientists have been trying to pinpoint the role of FMRP, or fragile X mental retardation protein, since they first linked it to fragile X syndrome 19 years ago. The new work supports the prevailing model that FMRP helps the brain make proteins at the synapse, the junction between neurons, even when the genetic instructions for doing so are located far away, in the nucleus.FMRP is an RNA-binding protein, and cell-culture experiments have found that its presence curbs the translation of RNA into protein. Bolstering this observation, mice that lack FMRP have excessive amounts of protein in their synapses, the junctions between neurons. The mutant mice also have abnormally long and dense dendritic spines — neuronal projections that receive signals from other cells — suggesting that FMRP aids in synaptic pruning, a crucial part of learning.The new studies suggest that FMRP acts as a kind of switch to repress translation of RNA into protein as the RNA is shuttled out of the nucleus, and reactivate translation once the RNA reaches its synaptic target.Read more at...SFARI, June 2010.