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Cadherins implement afferent-target matching in invertebrates, but proof for this concept in mammalian circuits has remained elusive. Two new studies in this issue of Neuron show that cadherin-6 mediates retinal ganglion cell target selection and that cadherin-9 promotes synapse specificity in the hippocampus. [ABSTRACT FROM AUTHOR]

A surprising new mechanism that regulates the plasticity of postnatal neurons is reported in this issue by . These authors show in mice that visual experience triggers cell-to-cell transfer of the homeoprotein Otx2 to cortical interneurons, where it promotes maturation of inhibitory neural circuitry and opens the critical period for plasticity in the visual cortex. [Copyright &y& Elsevier]

Stable genomic integration of exogenous transgenes is essential in neurodevelopmental and stem cell studies. Despite tools driving increasingly efficient genomic insertion with DNA vectors, transgenesis remains fundamentally hindered by the impossibility of distinguishing integrated from episomal transgenes. Here, we introduce an integration-coupled On genetic switch, iOn, which triggers gene expression upon incorporation into the host genome through transposition, thus enabling rapid and accurate identification of integration events following transfection with naked plasmids. In vitro , iOn permits rapid drug-free stable transgenesis of mouse and human pluripotent stem cells with multiple vectors. In vivo , we demonstrate faithful cell lineage tracing, assessment of regulatory elements, and mosaic analysis of gene function in somatic transgenesis experiments that reveal neural progenitor potentialities and interaction. These results establish iOn as a universally applicable strategy to accelerate and simplify genetic engineering in cultured systems and model organisms by conditioning transgene activation to genomic integration. • A gene expression switch powered by genomic integration • Accelerated readout of additive transgenesis with one or multiple vectors • Faithful lineage tracing and mosaic analysis by somatic transfection • Near-universal applicability in cultured cells and animal models Kumamoto et al. introduce iOn, a genetic switch that conditions exogenous transgene expression to integration in the host cell genome by DNA transposition. This system radically simplifies stable transgenesis with one or multiple plasmid vectors, opening new options to genetically manipulate cells in cultured systems and model organisms. [ABSTRACT FROM AUTHOR]