A Molecular Correlate of Ocular Dominance Columns in the Developing Mammalian Visual Cortex

Ocular dominance (OD) columns, alternating regions of left and right eye input in the visual cortex of higher mammals, have long been thought to develop from an initially intermingled state by an activity-dependent process. While indirect evidence points to potential alternative mechanisms based on molecular cues, direct proof for a molecular difference between left- and right eye columns is missing. Here, we show that heat shock protein 90 alpha (Hsp90) is expressed in a clustered fashion in the developing cat visual cortex. Clusters of Hsp90-positive cells are in register with OD columns of the ipsilateral eye as early as postnatal day 16, when OD columns have just appeared. Importantly, a periodic, clustered expression of Hsp90 is already present weeks before OD columns have started to form, suggesting that molecular differences between future left and right eye OD columns may contribute to the segregated termination of eye specific afferents in the developing visual cortex.