Beacon Molecule Nephronectin Guides Optic Nerve Cells to the Superior Colliculus during Development

Article: Scientists identify beacon molecule that prevents vision, behavioral problems in mice 
Source: Virginia Polytechnic Institute
Published: October 20, 2021 

Diagram of eye-specific retinocollicular projections

The superior colliculi (SC) are a pair of eminences at the "roof" of the midbrain where visual, auditory, and somatosensory information are integrated to initiate and coordinate movement. This brain region plays a central role in visual processing, receiving binocular input from 85-90% of retinal ganglion cells (as studied in the mouse brain), and projecting output signals to a variety of motor control centers in the cerebrum. The SC's processing capability stems from the precise organization of its cellular layers to refine signaling patterns. Neuroscientists are studying how axons from the eyes migrate during early brain development to form the optic nerve, including extending to regions such as the superior colliculus, in the hopes of identifying new ways to regenerate injured optic nerve fibers. Senior investigator of the study states, “If our goal is to one day regenerate damaged brain circuits to restore vision, then first we need to know how to get the cell’s axons to grow into a precise destination in the brain.” In particular, his team looked at how a specific subtype of optic nerve cells, ipsilateral retinal ganglion cells (ipsiRGCs), find their way to the superior colliculus during brain development. Using a viral tag, they identified two chaperon proteins that guide the circuit formation. One protein, a beacon molecule called nephronectin emitted by a type of excitatory neuron in the superior colliculus, attracts the optic nerve cells. Once the migrating cell has moved to the right location, nephronectin docks with a receptor protein on the migrating cell's membrane, telling the cell that it has reach its destination. Absence of nephronectin in mouse models results in the superior colliculus's visual layer not forming properly. The superior colliculus in the human brain occupies less relative volume, though it is also thought to play a role in "stabilizing our image of a moving world by controlling head, neck, and eye movements." Nonetheless, because the superior colliculus is present in all mammals, study of the signaling mechanisms that guide axons of different types of retinal neurons into segregated layers of brain regions provides a better understanding of the organizing principles of the visual system's segregated, parallel pathways. 

My rating of this study: ⭐⭐⭐

Su J, Sabbagh U, Liang Y, et al. "A cell–ECM mechanism for connecting the ipsilateral eye to the brain." PNAS.  118(42):e2104343118. 19 October 2021. https://doi.org/10.1073/pnas.2104343118