New study reveals microtubule retina band for energy transfer

A thick band of microtubules recently discovered in certain neurons in the retina could be the highway for mitochondria, organelles that provide energy to cells for vision.

Researchers from the National Heart, Lung, and Blood Institute and Yale University have discovered a microtubule band, a component of the cell’s cytoskeleton that extended from the axon of the neuron into the synaptic terminal and then looped around the interior periphery of the terminal. It appeared to associate with mitochondria in the synaptic terminal. The mitochondria accumulated in the axon of the neuron and did not reach the synaptic terminal upon the researchers’ administration of drug to inhibit the movement of certain “motor” proteins that transport mitochondria and other cargo within the cell by traveling along microtubules.

In addition to revealing the mitochondria transport medium function of these previously unknown microtubule structures, the study could help explain how bipolar synaptic terminals meet excessive energy demands.

The research, published in the July issue of The Journal of General Physiology (Graffe, M., et al. 2015. J. Gen. Physiol. doi:10.1085/jgp.201511396), examined the subcellular architecture of presynaptic terminals in retinal bipolar cells of live goldfish using cutting-edge 3D microscopy. The retinal bipolar cells of goldfish have giant presynaptic terminals that render them ideal for investigation.

The retina, a layer of tissue in the back of the eye that converts light into nerve impulses, contains small, specialized neurons called bipolar cells. These cells transmit information from light-sensitive photoreceptor cells to ganglion neurons, which in turn send information to the brain for interpretation. Unlike most other neurons, these cells are continuously active and require a constant supply of energy to mediate the sustained release of the contents of an enormous number of synaptic vesicles that store the transmitters conveying information between neurons.