Table 1. Specific roles for FMRP in neural circuit formation.
These studies demonstrate how specific neural circuits develop in FMRP-deficient organisms (dfmr1 null drosophila or Fmr1 null mice) or in wild-type organisms with dfmr1 or Fmr1 mutated in specific neuron populations.
| Organism | Circuit | Mutant phenotype | FMRP function | FMRP location | Ref. |
|---|---|---|---|---|---|
| Drosophila | NMJ | Increased connectivity; small terminal size; axon overgrowth | Restricts axon growth; presynaptic terminal growth | Axon | [43] |
| Drosophila | NMJ | Increased neurotransmission | - | Dendrite | [43] |
| Drosophila | MB | Axon overgrowth; increased connectivity | Restricts axon growth; axon pruning | Axon | [45] |
| Drosophila | CC | Axon overgrowth; increased connectivity | Synapse pruning | - | [46] |
| Mouse | SSC | Reduced connectivity; diffuse axon arbors; reduced plasticity | Activity-dependent axon refinement | - | [42] |
| Mouse | SSC | Reduced connectivity; hyperexcitability; decreased synchrony | - | - | [44] |
| Mouse | SSC | Increased spine turnover; immature spine shape | Spine stabilization; synapse maturation | - | [47] |
| Mouse | SSC | Increased spine turnover | Spine stabilization; synapse refinement | - | [48] |
| Mouse | DG | Increased connectivity; immature spine shape | Synapse maturation | - | [49] |
| Mouse* | CA1 | Increased connectivity | Synapse pruning | Dendrite | [50] |
| Mouse | SSC | Immature synapses; altered plasticity | Synapse maturation | - | [51] |
| Mouse | OBGC | Increased spines; immature spines; increased connectivity | Spine formation; synapse growth; dendrite refinement | Dendrite | [52] |
*
FMRP or FMRP mutant constructs were re-introduced into organotypic hippocampal slices from Fmr1 null mice. The mutant phenotypes and, when possible, the proposed function and location of FMRP are listed. NMJ: neuromuscular junction, MB: mushroom body, CC: circadian clock, SSC: somatosensory cortex, DG: dentate gyrus, CA1: hippocampus CA1 region, OBGC: olfactory bulb granule cells.