Genome-Wide Target Analyses of Otx2 Homeoprotein in Postnatal Cortex

Abstract

Juvenile brain has a unique time window, or critical period, in which neuronal circuits are remodeled by experience. Mounting evidence indicates the importance of neuronal circuit rewiring in various neurodevelopmental disorders of human cognition. We previously showed that Otx2 homeoprotein, essential for brain formation, is recaptured during postnatal maturation of parvalbumin-positive interneurons (PV cells) to activate the critical period in mouse visual cortex. Cortical Otx2 is the only interneuron-enriched transcription factor known to regulate the critical period, but its downstream targets remain unknown. Here, we used ChIP-seq (chromatin immunoprecipitation sequencing) to identify genome-wide binding sites of Otx2 in juvenile mouse cortex, and interneuron-specific RNA-seq to explore the Otx2-dependent transcriptome. Otx2-bound genes were associated with human diseases such as schizophrenia as well as critical periods. Of these genes, expression of neuronal factors involved in transcription, signal transduction and mitochondrial function was moderately and broadly affected in Otx2-deficient interneurons. In contrast to reported binding sites in the embryo, genes encoding potassium ion transporters such as KV3.1 had juvenile cortex-specific binding sites, suggesting that Otx2 is involved in regulating fast-spiking properties during PV cell maturation. Moreover, transcripts of oxidative resistance-1 (Oxr1), whose promoter has Otx2 binding sites, were markedly downregulated in Otx2-deficient interneurons. Therefore, an important role of Otx2 may be to protect the cells from the increased oxidative stress in fast-spiking PV cells. Our results suggest that coordinated expression of Otx2 targets promotes PV cell maturation and maintains its function in neuronal plasticity and disease.

Experience‐dependent transcriptional regulation in juvenile brain development

“…In contrast to the prevailing notion that PNN inhibits the plasticity as a physical barrier, a new study using mice lacking a key CS‐synthesizing enzyme, chondroitin sulfate N ‐acetylgalactosaminyltransferase 1 (CSGalNAcT1), showed that a small amount of PNN is essential to open the critical period by promoting accumulation of Otx2 in PV cells (Hou et al., ; Igarashi, Takeuchi, & Sugiyama, ). As CSGalNAcT1 is a target gene of Otx2 (Sakai et al., ), continuous internalization of Otx2 then accelerates further PNN formation, which in turn consolidates PV cell function and closes the critical period. Inhibition of Otx2 internalization in adults, by infusing a peptide that interferes with PNN interaction or by exogenous antibody to trap Otx2, leads to a decrease of PV circuits and reactivation of the critical period (Bernard et al., ; Beurdeley et al., ; Hou et al., ).…”

“…Otx2 co‐localizes mainly with PV cells across cortical regions such as somatosensory, motor, auditory and cingulate cortexes, and the emergence of Otx2 signals correlates with PV cell development (Sakai et al., ; Spatazza et al., ). Notably, it has been shown that auditory and medial prefrontal cortexes require localization of Otx2 in PV cells for the critical period (Lee et al., ).…”

“…Meanwhile, as a PV‐cell specific transcription factor during the maturation, Otx2 is the only known regulator. In order to explore genes under transcriptional regulation by Otx2, genomic regions bound by Otx2 were comprehensively analyzed by ChIP‐seq (chromatin immunoprecipitation—sequencing) using juvenile cortex (Sakai et al., ). Analysis of Otx2 bound genes, in combination with the interneuron‐specific transcriptome, suggests that Otx2 broadly affects expression of genes for transcription, neural development, signaling, and metabolism.…”

“…Remarkably, comparison of Otx2 binding sites between postnatal interneurons and embryonic progenitors (Hoch, Lindtner, Price, & Rubenstein, ) revealed that some potassium channel genes with postnatal‐specific Otx2 binding sites tended to be up‐regulated during PV cell maturation (Okaty et al., ). These included Kv3.1 family responsible for fast‐spiking of PV cells (Rudy & McBain, ), indicating that Otx2 may directly regulate genes for PV cell‐specific functions (Sakai et al., ; Figure b).…”

“…Interestingly, Otx2 defective interneurons showed dysregulated expression of genes for mitochondrial components and energy metabolism. Moreover, Otx2 binds to genes implicated in autophagy/mitophagy in a postnatal‐specific manner (Sakai et al., ). As PV cells have the fast‐spiking property, there is a high demand for energy metabolism, and as a result, the cells have a high risk of oxidative stress.…”