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

Koichi Tomita,Mark Hübener,Tobias Bonhoeffer,Max Sperling,Sidney B Cambridge

doi:10.1093/cercor/bhs232

Abstract

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 (Hsp90α) is expressed in a clustered fashion in the developing cat visual cortex. Clusters of Hsp90α-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 Hsp90α 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.

Highlights

The brain contains a number of sensory maps in which the outside world is represented in an orderly fashion
In order to identify candidate molecules differentially expressed in ocular dominance (OD) columns serving both eyes in the developing cat visual cortex, we devised a PCR-based differential screen followed by several confirmation steps to eliminate falsepositive clones (Fig. 1A) (Dulac and Axel 1995; Tanabe et al 1998)
The specificity of these clones was further examined by amplifying their cDNA inserts by PCR and subjecting the PCR products to Southern blots hybridized with the same cDNA probes from ipsi- and contralateral OD columns that were used in the differential screen (Fig. 1B)

Summary

Introduction

The brain contains a number of sensory maps in which the outside world is represented in an orderly fashion. Many of these maps develop under tight control of molecular cues, which guide growing axons toward their correct termination sites in the target region (Sperry 1963; Cheng et al 1995; Drescher et al 1995; Mombaerts et al 1996). Too, topographic map formation in sensory areas depends on the graded distribution of membrane bound guidance factors (Prakash et al 2000; Vanderhaeghen et al 2000; Dufour et al 2003; Cang, Kaneko et al 2005). OD columns are thought to develop from an initially uniform

Methods

Results

Conclusion