An actin-like component in spermatocytes of a crane fly (Nephrotoma suturalis Loew)

Decorated actin-like filaments were seen in spindles after crane fly spermatocytes were glycerinated and then treated with rabbit skeletal muscle heavy meromyosin (HMM). Both ATP and pyrophosphate inhibited the HMM reaction. In prometaphase, metaphase, and mid-anaphase cells, actin-like filaments were seen near regions where chromosomal spindle fibres are seen in living cells, and were oriented in the pole-to-pole direction. In the interzone of anaphase cells, actin-like filaments were not oriented in a preferential direction when they were not associated with the microtubules attached to the sex chromosomes. No filaments were seen in glycerinated spindles not treated with HMM. We discuss reasons why filaments might not be seen without prior HMM treatment, and we discuss the possible role of the actin-like filaments in the spindles. — Spindle microtubules often were not seen in cells treated with HMM. This depended on the stage of division: in prometaphase no microtubules were seen; in metaphase microtubules were seen, in apparently normal numbers; in mid-anaphase, microtubules between the autosomes and the poles were seen in reduced numbers, those associated with the equatorial sex-chromosomes were seen in apparently normal numbers, while those between the separating autosomal half-bivalents were not seen. Microtubules were not seen in glycerinated spindles not treated with HMM, suggesting that HMM in some way affects microtubule stability. The question of microtubule stability is briefly discussed.