Discovery of a Critical Switch for Eye Development - Rhianna Knable, 42041094

Scientists from the John Hopkins University School of Medicine and the Washington University School of Medicine have reached a breakthrough after identifying a vital step in the development of the human eye - the protein Pias3 has been found to regulate how light sensing nerve cells form in the retina, potentially allowing researchers to correct inherited blindness.

Pias3, or ‘protein inhibitor of activated stat3’, was known to affect gene control in the eye by adding a chemical tag to proteins responsible for switching genes on and off in a process called ‘SUMOylation’. Because Pias3 was only found in two other cells of the eye – developing rod and cone cells - the research team hypothesized that it might have an affect on what type of cells they eventually became. Rod cells function in less intense light than cone cells, and are responsible for vision at night or in dim/dark light, whereas cone cells help us see in brighter light and in colour. Dr Seth Blackshaw, a member of the research team, explains that "the loss of cone cells in particular can lead to irreversible blindness."

The structure of a cone cell (in this case from a bird), illustrating how it is responsible for the perception of colour.

The structure of a rod cell. 

To test their hypothesis about Pias3, the team experimented on mice, discovering that when they reduced the amount of Pias3 in the developing mice eyes, cells that might otherwise have been rod cells instead developed into cone cells. After reaching the conclusion that Pias3 must promote rod cell development and suppress cone cell development, the team wanted to understand exactly how this worked. By altering the Pias3 protein to disrupt its’ SUMOylation activity, it was found that the eyes did not develop the correct amount of rod cells, showing that SUMOylation is critical for its ability to repress cone development.

The researchers hope that these findings will contribute to clinical research into treatment options for blinding conditions caused by rod and cone cell death. Dr Blackshaw says "future treatments might be designed to manipulate Pias3-dependent SUMOylation and potentially convert photoreceptors to a cone fate, thus providing a treatment for forms of inherited blindness that selectively result in the death of cone photoreceptors."

Sources:
Original article: ScienceDaily (2009, March 15) ‘Critical Switch in Eye Development Discovered’, retrieved March 16, 2009 from http://www.sciencedaily.com/releases/2009/03/090309162117.htm
Images: http://upload.wikimedia.org/wikipedia/commons/2/29/BirdCone.png, http://upload.wikimedia.org/wikipedia/en/b/bb/Rod%26Cone.jpg