Opposing Morphogenetic Defects on Dendrites and Mossy Fibers of Dentate Granular Neurons in CRMP3-Deficient Mice.

Collapsin response mediator proteins (CRMPs) are highly expressed in the brain during early postnatal development and continue to be present in specific regions into adulthood, especially in areas with extensive neuronal plasticity including the hippocampus. They are found in the axons and dendrites of neurons wherein they contribute to specific signaling mechanisms involved in the regulation of axonal and dendritic development/maintenance. We previously identified CRMP3's role on the morphology of hippocampal CA1 pyramidal dendrites and hippocampus-dependent functions. Our focus here was to further analyze its role in the dentate gyrus where it is highly expressed during development and in adults. On the basis of our new findings, it appears that CRMP3 has critical roles both in axonal and dendritic morphogenesis of dentate granular neurons. In CRMP3-deficient mice, the dendrites become dystrophic while the infrapyramidal bundle of the mossy fiber shows aberrant extension into the stratum oriens of CA3. This axonal misguided projection of granular neurons suggests that the mossy fiber-CA3 synaptic transmission, important for the evoked propagation of the activity of the hippocampal trisynaptic circuitry, may be altered, whereas the dystrophic dendrites may impair the dynamic interactions with the entorhinal cortex, both expected to affect hippocampal function.

Altered expression of CRMPs in the brain of bovine spongiform encephalopathy-infected mice during disease progression.

While recent studies suggest that synaptic alterations are first events in the mechanisms of prion-mediated neurodegeneration, little is known on the identity of the neuronal plasticity-related genes potentially concerned. Here the expression of 4 Collapsin Response Mediator Proteins (CRMPs), a family of signal transduction proteins involved in brain development and altered in Alzheimer's disease, was studied in the brain of C57Bl/6 mice infected with the BSE strain of prion agent, using RT-PCR and Western-blot methods. At the terminal stage of the disease, gene expression of each CRMP had decreased, while at the mid-stage of the disease only CRMP4 (mRNA and protein) expression had increased, concomitant to the start of PrP(Sc) accumulation in the brainstem. Altogether our findings picked out originally CRMPs, and especially CRMP4, as potential contributors to prion pathogenesis.

Phosphorylation of collapsin response mediator protein 2 on Tyr-479 regulates CXCL12-induced T lymphocyte migration.

In the central nervous system, collapsin response mediator protein 2 (CRMP2) is a transducer protein that supports the semaphorin-induced guidance of axons toward their cognate target. However, we previously showed that CRMP2 is also expressed in immune cells and plays a crucial role in T lymphocyte migration. Here we further investigated the molecular mechanisms underlying CRMP2 function in chemokine-directed T-cell motility. Examining Jurkat T-cells treated with the chemokine CXCL12, we found that 1) CXCL12 induces a dynamic re-localization of CRMP2 to uropod, the flexible structure of migrating lymphocyte, and increases its binding to the cytoskeletal protein vimentin; 2) CXCL12 decreases phosphorylation of the glycogen synthase kinase-3beta-targeted residues CRMP2-Thr-509/514; and 3) tyrosine Tyr-479 is a new phosphorylation CRMP2 residue and a target for the Src-family kinase Yes. Moreover, phospho-Tyr-479 increased under CXCL12 signaling while phospho-Thr-509/514 decreased. The functional importance of this tyrosine phosphorylation was demonstrated by Y479F mutation that strongly reduced CXCL12-mediated T-cell polarization and motility as tested in a transmigration model and on neural tissue. We propose that differential phosphorylation by glycogen synthase kinase-3beta and Yes modulates the contribution of CRMP2 to cytoskeletal reorganization during chemokine-directed T-cell migration. In addition to providing a novel mechanism for T lymphocyte motility, our findings reveal CRMP2 as a transducer of chemokine signaling.

Processing and nuclear localization of CRMP2 during brain development induce neurite outgrowth inhibition.

Collapsin response mediator proteins (CRMPs) are believed to play a crucial role in neuronal differentiation and axonal outgrowth. Among them, CRMP2 mediates axonal guidance by collapsing growth cones during development. This activity is correlated with the reorganization of cytoskeletal proteins. CRMP2 is implicated in the regulation of several intracellular signaling pathways. Two subtypes, A and B, and multiple cytosolic isoforms of CRMP2B with apparent masses between 62 and 66 kDa have previously been reported. Here, we show a new short isoform of 58 kDa, expressed during brain development, derived from C-terminal processing of the CRMP2B subtype. Although full-length CRMP2 is restricted to the cytoplasm, using transfection experiments, we demonstrate that a part of the short isoform is found in the nucleus. Interestingly, at the tissue level, this short CRMP2 is also found in a nuclear fraction of brain extract. By mutational analysis, we demonstrate, for the first time, that nuclear translocation occurs via nuclear localization signal (NLS) within residues Arg(471)-Lys(472) in CRMP2 sequence. The NLS may be unmasked after C-terminal processing; thereby, this motif may be surface-exposed. This short CRMP2 induces neurite outgrowth inhibition in neuroblastoma cells and suppressed axonal growth in cultured cortical neurons, whereas full-length CRMP2 promotes neurite elongation. The NLS-mutated short isoform, restricted to the cytoplasm, abrogates both neurite outgrowth and axon growth inhibition, indicating that short nuclear CRMP2 acts as a dominant signal. Therefore, post-transcriptional processing of CRMP2 together with its nuclear localization may be an important key in the regulation of neurite outgrowth in brain development.

Differential expression of CRMP1, CRMP2A, CRMP2B, and CRMP5 in axons or dendrites of distinct neurons in the mouse brain.

CRMP1, CRMP2, and CRMP5 have been identified as cytosolic proteins relaying semaphorin 3A signalling, one of the molecular cues conducting axon and dendrite growth and guidance. They are highly expressed during brain ontogenesis, but, because of their lower levels in the adult, their distribution in the mature brain is poorly documented. By using specific antibodies, we investigated the cellular distribution of these CRMPs in different adult brain structures and in neural cell cultures with a special focus on the splice variants CRMP2A and CRMP2B. In brain sections of adult mouse, CRMP1, CRMP2B, and CRMP5 were located predominantly in dendrites of specific neuronal populations, such as cortical pyramidal neurons, hippocampal CA1 pyramidal cells, or Purkinje cerebellar cells. On the contrary, CRMP2A was specifically associated with axons of the corpus callosum, bundles of the striatum, and mossy fibers of the hippocampus. In cultures of cortical neurons, CRMP1, CRMP2A, CRMP2B, and CRMP5 were equally distributed throughout cell bodies, axons, or dendrites of neurons, whereas CRMP2A and CRMP5 were completely absent from Purkinje cerebellar cells in 12-day-old animals. By comparison, oligodendrocytes exclusively express CRMP2B and CRMP5 in cell bodies and processes both in situ in the adult brain and in primary cultures. Overall, our results demonstrate specific subcellular localizations of CRMP1, CRMP2A, CRMP2B, and CRMP5 depending on cell types, neuronal compartment, and developmental stage. This study suggests that, beyond their signalling function in axon outgrowth and guidance, CRMPs also play a role in mature neurons both in axons and in dendrites.