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Keilin's Organs (KO), are sensory structures found in some species of insects in the order Diptera, such as the fruit fly, Drosophila melanogaster. They are derived from rudimentary larval legs, and are innervated by five sensory neurons of the peripheral nervous system. They are present in each of the three thoracic segments of the fly embryo, close to the ventral midline. Each Keilin's organ consists of three short hairs that are approximately 5µM long. Keilin's organs are present in the larval stage of fruit fly development but disappear during metamorphosis. They were named after the influential entomologist, David Keilin.



Keilin's organs develop from cellular structures called imaginal discs. Imaginal discs are clusters of cells which organize in the embryonic stage of development and acquire specific patterns of gene expression. Imaginal discs persist in the larval stage of development, and subsequently give rise to macroscopic adult structures such as legs, wings, antennae, and halteres. The Keilin's organs arise from the same imaginal discs that later give rise to the three pairs of legs found in adult individuals of D. melanogaster.

Development of Keilin's organs requires expression of the homeotic gene gene Distalless (Dll), a member of the DLX gene family in Drosophila. The cells in the imaginal discs that develop into the legs and wings also require expression of Dll, however, activation of a specific enhancer element, DKO, will lead to development of the Keilin's organs in that specific subset of cells. Ectopic expression of these genes may lead to the ectopic development of Keilin's organs. In the absence of Dll expression, Keilin's organs fail to develop.