Molecularly Defined Circuitry Reveals Input-Output Segregation in Deep Layers of the Medial Entorhinal Cortex

Deep layers of the medial entorhinal cortex are considered to relay signals from the hippocampus to other brain structures, but pathways for routing of signals to and from the deep layers are not well established. Delineating these pathways is important for a circuit level understanding of spatial cognition and memory. We find that neurons in layers 5a and 5b have distinct molecular identities, defined by the transcription factors Etv1 and Ctip2, and divergent targets, with extensive intratelencephalic projections originating in layer 5a, but not 5b. This segregation of outputs is mirrored by the organization of glutamatergic input from stellate cells in layer 2 and from the hippocampus, with both preferentially targeting layer 5b over 5a. Our results suggest a molecular and anatomical organization of input-output computations in deep layers of the MEC, reveal precise translaminar microcircuitry, and identify molecularly defined pathways for spatial signals to influence computation in deep layers. •The transcription factors Etv1 and Ctip2 distinguish entorhinal layers 5a and 5b•Layer 5a has extensive intratelencephalic projections, but layer 5b does not•Terminals of layer 2 stellate, but not pyramidal cells, are enriched in deep layers•Hippocampal and stellate cell inputs preferentially target layer 5b neurons Sürmeli et al. demonstrate that input and output functions of the deep layers of the medial entorhinal cortex are divided between two cell populations that are distinguished by their molecular identity, lamina position, translaminar and hippocampal inputs, and telencephalic targets.