(A) In situ mRNA hybridization showing the expression pattern for Robo1, Robo2 and Slit1,2,3 in the early postnatal and mature mouse hippocampus. Robo2, Slit1,3 are expressed in all CA regions in the hippocampus, Robo1 and Slit2 expression is confined to CA3. Robo2 expression increases between P4 and P14. Scale bar: 50μm.
(B) Immunohistochemistry for FLRT2 (red) and Robo2 (green) proteins in the rat hippocampus at P35. While FLRT2 is expressed throughout all layers in CA1, expression of Robo2 is confined to SO and SR. Scale bar: 100μm. SR, stratum radiatum; SLM, stratum lacunosum-moleculare; ML, molecular layer of DG; SO, stratum oriens; SP, stratum pyramidale.
(C) Subcellular localizationofRobo2 in vitro. Ex utero electroporation of Robo2-pHluorin and Homer1-c-tdtomato in pyramidal neurons in vitro. Robo2-pHluorin colocalizes with the excitatory post-synapticmarker Homer1c at the majority of dendritic spines at 14 DIV. Scale bar: 15μm.
(D) Synaptic fractionation and immunoblot for Robo2, Slit2 and synaptic markers. Successful isolation of pre-and postsynaptic compartments is validated by presence of synaptophysin and PSD95 respectively. Robo2 localizes to pre-and post-synaptic compartments, its ligand Slit2 is enriched presynaptically.
(E) Schematic of hippocampal circuit connectivity.