title: Measurements of forces produced by the mitotic spindle using optical tweezers.
abstract: We used a trapping laser to stop chromosome movements in Mesostoma and crane-fly spermatocytes and inward movements of spindle poles after laser cuts across Potorous tridactylus (rat kangaroo) kidney (PtK2) cell half-spindles. Mesostoma spermatocyte kinetochores execute oscillatory movements to and away from the spindle pole for 1-2 h, so we could trap kinetochores multiple times in the same spermatocyte. The trap was focused to a single point using a 63× oil immersion objective. Trap powers of 15-23 mW caused kinetochore oscillations to stop or decrease. Kinetochore oscillations resumed when the trap was released. In crane-fly spermatocytes trap powers of 56-85 mW stopped or slowed poleward chromosome movement. In PtK2 cells 8-mW trap power stopped the spindle pole from moving toward the equator. Forces in the traps were calculated using the equation F = Q'P/c, where P is the laser power and c is the speed of light. Use of appropriate Q' coefficients gave the forces for stopping pole movements as 0.3-2.3 pN and for stopping chromosome movements in Mesostoma spermatocytes and crane-fly spermatocytes as 2-3 and 6-10 pN, respectively. These forces are close to theoretical calculations of forces causing chromosome movements but 100 times lower than the 700 pN measured previously in grasshopper spermatocytes.
authors.affiliation: Department of Biology, York University, Toronto, ON M3J 1P3, Canada. ferraroj@yorku.ca
authors.forename: Jessica
authors.initials: J
authors.lastname: Ferraro-Gideon
authors.forename: Rozhan
authors.initials: R
authors.lastname: Sheykhani
authors.forename: Qingyuan
authors.initials: Q
authors.lastname: Zhu
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Duquette
authors.forename: Michael W
authors.initials: MW
authors.lastname: Berns
authors.forename: Arthur
authors.initials: A
authors.lastname: Forer
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002460:Cell Line; D004175:Diptera; D018386:Kinetochores / Q000502:physiology; D008297:Male; D008938:Mitosis; D052898:Optical Tweezers; D010986:Platyhelminths; D048328:Potoroidae; D013090:Spermatocytes / Q000648:ultrastructure; D008941:Spindle Apparatus / Q000502:physiology* / Q000648:ultrastructure