Microglial Interactions with Synapses Are Modulated by Visual Experience

Microglia, the brain's immune cells, show unique interactions with nearby synaptic elements under non-pathological conditions that are sensitive to changes in sensory experience

Cryptic speciation in a model invertebrate chordate

We applied independent species concepts to clarify the phylogeographic structure of the ascidian Ciona intestinalis, a powerful model system in chordate biology and for comparative genomic studies. Intensive research with this marine invertebrate is based on the assumption that natural populations globally belong to a single species. Therefore, understanding the true taxonomic classification may have implications for experimental design and data management. Phylogenies inferred from mitochondrial and nuclear DNA markers accredit the existence of two cryptic species: C. intestinalis sp. A, genetically homogeneous, distributed in the Mediterranean, northeast Atlantic, and Pacific, and C. intestinalis sp. B, geographically structured and encountered in the North Atlantic. Species-level divergence is further entailed by cross-breeding estimates. C. intestinalis A and B from allopatric populations cross-fertilize, but hybrids remain infertile because of defective gametogenesis. Although anatomy illustrates an overall interspecific similarity lacking in diagnostic features, we provide consistent tools for in-field and in-laboratory species discrimination. Finding of two cryptic taxa in C. intestinalis raises interest in a new tunicate genome as a gateway to studies in speciation and ecological adaptation of chordates

Specific involvement of postsynaptic GluN2B-containing NMDA receptors in the developmental elimination of corticospinal synapses

The GluN2B (GluRε2/NR2B) and GluN2A (GluRε1/NR2A) NMDA receptor (NMDAR) subtypes have been differentially implicated in activity-dependent synaptic plasticity. However, little is known about the respective contributions made by these two subtypes to developmental plasticity, in part because studies of GluN2B KO [Grin2b−/− (2b−/−)] mice are hampered by early neonatal mortality. We previously used in vitro slice cocultures of rodent cerebral cortex (Cx) and spinal cord (SpC) to show that corticospinal (CS) synapses, once present throughout the SpC, are eliminated from the ventral side during development in an NMDAR-dependent manner. To study subtype specificity of NMDAR in this developmental plasticity, we cocultured Cx and SpC slices derived from postnatal day 0 (P0) animals with different genotypes [2b−/−, Grin2a−/− (2a−/−), or WT mice]. The distribution of CS synapses was studied electrophysiologically and with a voltage-sensitive dye. Synapse elimination on the ventral side was blocked in WT(Cx)-2b−/−(SpC) pairs but not in WT(Cx)-2a−/−(SpC) or 2b−/−(Cx)-WT(SpC) pairs. CS axonal regression was also observed through live imaging of CS axons labeled with enhanced yellow fluorescent protein (EYFP) through exo utero electroporation. These findings suggest that postsynaptic GluN2B is selectively involved in CS synapse elimination. In addition, the elimination was not blocked in 2a−/− SpC slices, where Ca2+ entry through GluN2B-mediated CS synaptic currents was reduced to the same level as in 2b−/− slices, suggesting that the differential effect of GluN2B and GluN2A in CS synapse elimination might not be explained based solely on greater Ca2+ entry through GluN2B-containing channels