Andrea Alonzo 812000494
Ria Ramcharitar 812000177
Kamine Saroop 812002265
Short Distance Communication Between Cells
The Drosophila, also commonly known as the fruit fly, has very complex eyes called Compound Eyes. These compound eyes contain 750 ommatida arranged in a spherical formation. Each ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The pigment cells separate each ommatidium from its neighbors. When visual information enters the eye via the retina, which contains photoreceptors R1-8 in individual ommatidium (six out of the eight photoreceptors are white, R7 is purple and R8 is green).
There are many cell communications happening in the compound eye in order for vision to occur, however we will be focusing specifically on the communication between the photoreceptor cells and its neighboring pigment cells. This will be local signaling since the cells are close to each other.
Autocrine signaling- cell secretes chemical messengers (autocrine agent) which binds to autocrine receptors of the same type of cell. A Photoreceptor cell will use autocrine signaling to communicate with another photoreceptor cell. There are 3 stages of signaling => signal transduction pathway:
· Reception of the signal by a cell
Communication between R8 and R7: the autocrine agent [transmembrane ligand Bride of Sevenless (Boss)] binds to the receptor known as Tyrosin Kinase Sevenless (SEV).
· Transduction (from the outside of the cell to the inside)
This mechanism is trasduced by Ras activation within the R7 cell.
Recall: R7 is purple photoreceptor cell
Less light will be absorbed so that the fly is not blinded by ambient light.
Paracrine signaling– this is a type of cell-cell communication where cells produces signals to induce a change in neighboring cells (altering the behavior or differentiation of those cells).
Responsible for color vision
Below is a video discussing the structure and function of the ommatidium.
Importance of communication between photoreceptor cells and pigment cells
The red screening pigment of the pigment cells optically isolates the ommatida. The photoreceptor cells contain yellow screening pigment which is responsible for papillary responses. The light sensitive region of the photoreceptor cell is known as the rhabdomere. The Rhabdomere is composed of 30,000 microvilli which are responsible for capturing photons of light to a quantum bump, which is then responsible for the depolarization of the photoreceptor cell membrane. The membrane is packed with approximately 1000 pigment cells that make the Rhabdomere optically dense and provide a guide for light. The pigment cells ensures that only light entering the ommatidium parallel or nearly parallel to its long axis reaches the visual cells and triggers nerve impulses. Expression of pigments in photoreceptor cells determines color vision in the fruit fly.
Below shows the structure of the ommatidia.