Rearing Mesostoma ehrenbergii and studying chromosome movements during meiosis in their spermatocytes

"The Mesostoma ehrenbergii spermatocyte is an advantageous cell for studying meiosis. Its many unique features include regular and persistent bivalent kinetochore oscillations, distance segregation of univalents and the presence of a precocious cleavage furrow. In studying these unconventional aspects of meiosis in one cell, I concentrated on studying which components are involved in the force production driving chromosome movement, using bivalent kinetochore oscillations as a measurable conversion. Mesostoma spermatocytes had not been well studied and there are only a handful of articles in the literature that describe them so l first had to characterize their normal behaviour. I determined that kinetochore movement to the pole is faster than kinetochore movement away from the pole; bivalents enter into anaphase in the middle of an oscillation cycle as there is no definable metaphase; bivalents reorient (and kinetochores switch poles) after achieving bipolar orientation; and univalents move multiple times between spindle poles. After characterizing kinetochore oscillations in these spermatocytes, I used an ultraviolet microbeam, an optical cutting laser and an optical trapping laser as tools to study the components involved in driving kinetochore movements to and away from the pole. The results from my UV microbeam and laser microbeam experiments suggest that different mechanisms are required to produce kinetochore movement to the pole versus away from the pole, and that non-microtubule components and/or a spindle matrix are involved as kinetochores still moved to the pole in the absence of microtubule continuity between kinetochore and pole. Comparisons of normal bivalent reorientations, where partner kinetochores switch poles, with laser-induced reorientations, where partners retain their original orientations, suggest that the segregation of bivalents is non-random. UV irradiations indicated that the cleavage furrow changes positions in response to alterations in spindle components. Severed chromosome arms moved to the other arm, indicating that there is a connection (""tether"") between bivalent arms. The results from my optical trapping experiments determined that the force produced by the spindle to move chromosomes to the pole is one one-hundredth of 700pN that was originally measured and is close to the theoretical values."