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

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.