External Sensory Organ Development
The Drosophila external sensory organ is a sensory structure in the peripheral nervous system that consists of four cells; a neuron, a sheath cell that surrounds the dendrite, and hair and socket cells, which are considered the “outer” support cells. All four cell fates are descendants of the sensory organ precursor (SOP) cell. In response to the proper cues, SOPs first divide into two secondary precursor cells. The posterior daughter cell is called the pIIa cell and the anterior daughter cell is called the pIIb. The pIIa cell divides to produce a bristle cell and a socket cell, while the pIIb cell divides to produce a neuron and a glial cell. The asymmetric division of the SOP into daughter cells with distinct fates is dependent upon the distribution of Numb. Numb is distributed uniformly in the cytoplasm until mitotic division, when it is selectively localized to the anterior pole of the cell. Thus, Numb is selectively segregated into the pIIb daughter cell upon division of the SOP.
Loss of Numb function causes inappropriate differentiation of SOP cells into all pIIa cells, producing four outer support cells and no neurons or glia. In SOP loss of function Numb mutants, flies have a significant decrease in sensory neurons, leaving them “numb.” Gain of function Notch mutants express a similar phenotype. Ectopic expression of Numb during SOP division has the opposite effect, producing all pIIb cells and no outer support cells. In support of previous experiments demonstrating the role of Numb in Notch signaling inhibition, functional loss of Notch signaling components result in SOP division into two pIIb cells, suggesting Numb promotes acquisition of the pIIb cell fate through inhibition of Notch signaling. Thus, the asymmetric distribution of Numb into IIb secondary precursors during SOP division is necessary for daughter cells to acquire distinct cell fates.
Famous quotes containing the words development, organ, external and/or sensory:
“The development of civilization and industry in general has always shown itself so active in the destruction of forests that everything that has been done for their conservation and production is completely insignificant in comparison.”
—Karl Marx (18181883)
“What we commonly call man, the eating, drinking, planting, counting man, does not, as we know him, represent himself, but misrepresents himself. Him we do not respect, but the soul, whose organ he is, would he let it appear through his action, would make our knees bend.”
—Ralph Waldo Emerson (18031882)
“When a person hasnt in him that which is higher and stronger than all external influences, it is enough for him to catch a good cold in order to lose his equilibrium and begin to see an owl in every bird, to hear a dogs bark in every sound.”
—Anton Pavlovich Chekhov (18601904)
“Ours is a culture based on excess, on overproduction; the result is a steady loss of sharpness in our sensory experience. All the conditions of modern lifeits material plenitude, its sheer crowdednessconjoin to dull our sensory faculties.”
—Susan Sontag (b. 1933)