COORDINATED MOVEMENTS BETWEEN AUTOSOMAL HALF-BIVALENTS IN CRANE-FLY SPERMATOCYTES - EVIDENCE THAT STOP SIGNALS ARE SENT BETWEEN PARTNER HALF-BIVALENTS

During anaphase-I in crane-fly spermatocytes, sister half-bivalents se parate and move to opposite poles, When we irradiate a kinetochore spi ndle fibre with an ultraviolet microbeam, the associated half-bivalent temporarily stops moving and so does the partner half-bivalent with w hich it was paired during metaphase, To test whether a 'signal' is tra nsmitted between partner half-bivalents we irradiated the spindle twic e, once in the interzone (the region between separating partner half-b ivalents) and once in a kinetochore fibre, For both irradiations we us ed light of wavelength 290 mu m and a dose that, after irradiating a s pindle fibre only, altered movement in 63% of irradiations (12/19); in 11 of the 12 cells both partner half-bivalents stopped moving after t he irradiation. In control experiments we irradiated the interzone onl y: these irradiations generally did not stop chromosomal poleward moti on but sometimes (14/29) caused poleward movement to each pole to be a bruptly reduced to about half the velocity prior to irradiation. In do uble irradiation experiments we varied the order of the irradiations. In some double irradiation experiments we irradiated the interzonal re gion first and the spindle fibre second; in 75% (9/12) of the cells th e half-bivalent associated with the irradiated fibre stopped moving wh ile the partner half-bivalent moved normally, i.e. in 9/12 cells the i nterzonal irradiations uncoupled the movements of the partner half-biv alents. In other double irradiation experiments we irradiated the spin dle fibre first and the interzone second: in 80% (4/5) of the cells th e half-bivalents not associated with the irradiated spindle fibre resu med movement immediately after the irradiation while the other half-bi valent remained stopped, Interzonal irradiations therefore uncouple th e poleward movements of sister half-bivalents and the uncoupling does not depend on the order of the irradiation, Our experiments suggest th erefore that the irradiation of a spindle fibre causes negative ('stop ') signals to be transmitted across the interzone and that irradiation of the interzone blocks the transmission of the stop signal.