Our laboratory has been working for several years on the role of non-cell autonomous homeoprotein transcription factors in regulating cerebral cortex physiology. We have shown that in mice the OTX2 homeoprotein is expressed in the choroid plexus, secreted into cerebrospinal fluid, and transferred into parvalbumin (PV)-expressing interneurons. OTX2 participates in PV cell maturation and regulates the timing of plasticity critical periods. These juvenile periods allow for remodeling of circuitry in response to the environmental and genetic contexts. They not only occur in primary sensory cortices but also in associative cortices such as the medial prefrontal cortex (mPFC). Consequently, they are associated with disease outcomes and support the neurodevelopmental hypothesis for some psychiatric disorders. Although our initial OTX2 studies were primarily focused on mouse visual system critical periods, we have also investigated higher order circuits including mPFC. Indeed, other labs have recently reported causal links between OTX2 and anxiety-like behavior in rodents induced by early-life stress. I will detail what is known about OTX2 transfer in the postnatal brain regarding its target cells and genes, and will present recent findings showing that choroid plexus OTX2 affects adult mouse brain plasticity and animal behavior.