Kinetochore microtubules in crane‐fly spermatocytes: Untreated, 2°C‐treated and 6°C‐grown spindles

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Abstract
We investigated the involvement of kinetochore microtubules (kMTs) in mediating chromosome‐to‐pole connections in crane‐fly (Nephrotoma suturalis and Nephrotoma ferruginea) spermatocytes. Two experimental treatments were used to yield spindles with reduced numbers of nonkinetochore microtubules (nkMTs). Short‐term (10–15 min) exposure of spermatocytes to 2°C caused depolymerization of the majority of nkMTs, resulting in a kMT:(kMT + nkMT) ratio of 0.76. Long‐term (24h) exposure to 2°C followed by recovery at 6°C resulted in a kMT:(kMT + nkMT) ratio of 0.55, the spindle having more nkMTs than a 2°C‐treated spindle but fewer than an untreated spindle, in which the kMT:(kMT + nkMT) ratio was 0.27. The numbers and lengths of kMTs in 6°C‐grown spindles were similar to those in untreated cells, suggesting that the overall inhibition of MT assembly at 6°C apparently did not affect the mechanism by which kMTs are formed. We observed most kMTs of early anaphase spindles to be long (>3 μm), and many extended to the polar regions of the spindle. Thus, the crane‐fly spindle appears not to be as atypical as it was previously suggested to be.