Understanding the Structural and Developmental Aspect of Simple Eye of Drosophila: The Ocelli

Among various photoreceptors present in arthropods Drosophila eye undergoes certain modification to provide high resolution and sensitivity to the animal. Along with the compound eye Drosophila possess three ocelli for its vision, navigation and locomotion purpose. These ocelli are arranged in a triangular manner in between the compound eye. During third instar larvae, from the eye antenna imaginal disc several conserved genes and complex regulatory genetic network help in ocellar patterning. Like compound eye ocelli possess cornea, corneagenous cell, photoreceptor cells (rhabdom). The visual pigment present in ocelli is Rh2 and is responsible for the functioning of ocelli. Although rhabdomere are the photoreceptor organ of the ocelli the arrangement of the rhabdomere in ocelli differs from the compound eye. Interrhabdomereal space which is present between the rhabdomeres of photoreceptor cells are absent in ocelli. The rhabdom is confined only to the apical one-third of the ocelli whereas it expands throughout the length in compound eye. The structural difference present in the compound eye and ocelli enable us to study the functioning of one gene in different photoreceptors within an animal. Thus understanding the mechanism of ocellar development, genes involved in the functioning of ocelli will help us to understand the functioning of various genes in different photoreceptor. The current article summarises the structure, function and genes involved in the development of ocelli.