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Journal of Cell Science, Vol 88, 441-452, Copyright © 1987 by Company of Biologists

Submitted on June 1, 1987
Accepted on July 24, 1987

Sex-chromosome anaphase movements in crane-fly spermatocytes are coordinated: ultraviolet microbeam irradiation of one kinetochore of one sex chromosome blocks the movements of both sex chromosomes

JULIA A. M. SWEDAK 1 and ARTHUR FORER 1

1 Biology Department, York University, Downsview, Ontario, Canada, M3J 1P3

Sex chromosomes in crane-fly spermatocytes move polewards at anaphase after the autosomes have reached the poles. In Nephrotoma abbreviate the sex chromosomes are 8 µm long by 3.5 µm wide and have two orientations when they move: the long axis of the sex chromosome is either perpendicular or parallel to the spindle axis. We assume (1) that when a sex chromosome is perpendicular to the spindle axis it has a chromosomal spindle fibre to each pole, one from each kinetochore, as in other species; and (2) that when a sex chromosome is parallel to the spindle axis each kinetochore has spindle fibres to both poles, i.e. that the latter sex chromosomes are maloriented.

We irradiated one kinetochore of one sex chromosome using an ultraviolet microbeam. When both sex chromosomes were normally oriented, irradiation of a single kinetochore permanently blocked movement of both sex chromosomes. Irradiation of non-kinetochore chromosomal regions or of spindle fibres did not block movement, or blocked movement only temporarily. We argue that ultraviolet irradiation of one kinetochore blocks movement of both sex chromosomes because of effects on a ‘signal’ system. The results were different when one sex chromosome was maloriented. Irradiation of one kinetochore of a maloriented sex chromosome did not block motion of either sex chromosome. On the other hand, irradiation of one kinetochore of a normally oriented sex chromosome permanently blocked motion of both that sex chromosome and the maloriented sex chromosome. We argue that for the signal system to allow the sex chromosomes to move to the pole each sex chromosome must have one spindle fibre to each pole.

Key words: sex chromosome movement, spermatocytes, crane-fly, ultraviolet microbeam

Submitted on June 1, 1987
Accepted on July 24, 1987




This article has been cited by other articles:


Home page
 J. Cell Sci.Home page
B Yin and A Forer
Coordinated movements between autosomal half-bivalents in crane-fly spermatocytes: evidence that 'stop' signals are sent between partner half-bivalents
J. Cell Sci., January 1, 1996; 109(1): 155 - 163.
[Abstract] [PDF]


© The Company of Biologists Ltd 1987