Microtubules and Sensory Transduction

Abstract

Cockroach legs bear tactile spines equipped with campaniform sensilla-mechanoreceptors associated with the cuticle-which function by a single bipolar neuron from whose dendrite tip extends a modified cilium packed with 350-1000 parallel cytoplasmic microtubules. These microtubules, which can be chemically disassembled with colchicine and vinblastine, are intimately associated with the site of mechanical stimulation. Treatment of living sensilla with colchicine and vinblastine abolishes their ability to respond to mechanical stimulation 1-2 hr after drug application. Loss of function is accompanied by large-scale disassembly of microtubules in the modified cilium. The experimental evidence strongly suggests that microtubules play an important role in the process of sensory transduction in campaniform sensilla.The purpose of this study is to investigate the role of microtubules, if any, in mechanoreception. We selected campaniform sensilla on cockroach legs as an experimental system because they are accessible for investigation and have numerous microtubules at the site of stimulus reception. Each sensillum functions with only one bipolar neuron. This primary sense cell singly handles the functions of stimulus reception, transduction, and impulse transmission. The dendrite tip, like that of other ciliated mechanoreceptors, contains a basal body from which extends a long, microtubule-packed, modified cilium. The tip of the modified cilium, called the sensory process, is a membrane-limited bundle of 350-1000 parallel microtubules that attaches directly to the site of mechanical stimulation on the cuticle (Figs. 1 and 2). In order to determine whether microtubules are necessary components for mechanoreception in campaniform sensilla, we investigated the effects of chemical disassembly of microtubules. Our experimental evidence shows that chemical disassembly of the microtubules of the sensory process by colchicine or vinblastine is accompanied by loss of mechanosensitivity of sensilla. ity from a single campaniform sensillum located in the cuticle at the front of the base of the spine. Because of the geometry of the spine and the placement of its campaniform sensillum, touching the tactile spine effectively stimulates the sensillum to produce a burst of nerve impulses. Fig. 1

Cytofluorometric studies on the action of podophyllotoxin and epipodophyllotoxins (VM-26, VP-16-213) on the cell cycle traverse of human lymphoblasts.

“…cal (1,12,16,23), biochemical, and physiological changes (5,(17)(18)(19)24) seen apparently as a direct consequence of this affinity between tubulin and the c-mitotic agents such as colchicine and the vinca alkaloids, vinblastine and vincristine. At the morphological level, a prominent manifestation of this affinity between some of the c-mitotic drugs and tubulin is seen in the destruction of the mitotic spindle and accumulation of cells in mitosis.…”

Laser-induced spreading arrest of Mytilus gill cilia.

“…Similar events without permanent injury probably occur after mechanical stimulation. This is the type of transduction sequence that has been considered for mechanoreceptive phenomena in ciliary-based systems in general (Thurm, 1968;Eckert, 1972;Moran and Varela, 1971;Gilula and Satir, 1972;Mackie et al, 1974).…”

The dynein–tubulin motor powers active oscillations and amplification in the hearing organ of the mosquito

“…To identify the molecular machinery underlying the SOs, we have studied the temperature-dependence of the SOs and their sensitivity to colchicine, which is known to depolymerize the microtubules in the cilia of scolopidial units (Moran & Varela 1971) and would perturb the SO if it receives contributions from the active beat of sensory cilia.…”