Updated project metadata. Cajal-Retzius (CR) cells are a transient neuron type that populate the postnatal hippocampus. The role of transient cell types and circuits have been vastly addressed in neocortical regions, but poorly studied in the hippocampus. To understand how CR cells persistence influences the maturation of hippocampal circuits, we specifically ablated CR cells from the postnatal hippocampus. We observed layer-specific changes in the dendritic complexity and spine density of CA1 pyramidal cells. We were able to identify significant changes in the expression levels of Latrophilin-2, a postsynaptic guidance molecule known for its role in the entorhinal-hippocampal connectivity. Those findings were supported by changes in the overall synaptic proteomic content in CA1 Stratum Lacunosum-Moleculare.