Switching from Blue to Green

Science Signaling  29 Jul 2008:
Vol. 1, Issue 30, pp. ec271
DOI: 10.1126/scisignal.130ec271

Fly larvae have "eyes" that help the larvae avoid light and contribute to entraining the circadian clock to light. Each eye is composed of four photoreceptor cells that sense blue light and eight photoreceptor cells that sense green light. The wavelength of light detected is controlled by the presence of particular rhodopsins, specifically Rh5 for blue light and Rh6 for green light. This larval eye metamorphoses into an organ called the eyelet that contains four Rh6 photoreceptors and is involved only in entraining the circadian clock in the adult. By tagging the eye cells in the larvae, Sprecher and Desplan found that the eight Rh6 photoreceptor cells died and the four Rh5 photoreceptor cells switched their rhodopsin expression profile to become Rh6 photoreceptor cells in the adult eyelet. The hormone ecdysone, which is a master regulator of metamorphosis, was required for the development of the eyelet. If the function of the ecdysone receptor (EcR) was compromised in the larval Rh6 cells, then an eyelet formed with 12 Rh6 photoreceptor cells. If EcR function was blocked only in the Rh5 cells, then these cells failed to undergo the switch to become Rh6 photoreceptor cells, thus producing a four-cell eyelet with Rh5 photoreceptors. The transcription factor Senseless (Sens), which was only present in the larval Rh5 photoreceptor cells, was required for survival of the Rh5 photoreceptor cells. If misexpressed in the larval Rh6 photoreceptor cells, those cells survived, producing the enlarged Rh6 photoreceptor eyelet with 12 cells. The change from Rh5 to Rh6 photoreceptor is an example of sensory plasticity and fate switching of differentiated cells.

S. G. Sprecher, C. Desplan, Switch of rhodopsin expression in terminally differentiated Drosophila sensory neurons. Nature 454, 533-537 (2008). [PubMed]