Quantitative studies on the polarization optical properties of living cells II. The role of microtubules in birefringence of the spindle of the sea urchin egg.

Abstract

Birefringence of the mitotic apparatus (MA) and its change during mitosis in sea urchin [Clypeaster japonicus] eggs were quantitatively determined using the birefringence detection apparatus. The birefringence and the form of the MA are represented by 5 parameters: peak retardation (.delta.p), trough retardation (.delta.t), interpolar distance (D1) the distance (D2) between chromosome groups moving toward poles and the distance (D3) between 2 retardation peaks. Distributions of birefringence retardation and the coefficient of birefringence in the spindle were quantitatively determined in MAs isolated during metaphase and anaphase. The distribution of microtubules (MTs) contained in the spindle was determined in isolated MAs, assuming that the observed birefringence of the spindle is attributable to the form birefringence caused by regularly arranged MTs. The distribution coincided fairly well with the distribution of MTs in isolated MAs determined by EM. Under the same assumption, the distribution of MTs in the spindle in living cells during mitosis was determined. The distribution of MTs and the total amount of polymerized tubulin (MTs) in the spindle change during mitosis, suggesting the assembly and disassembly of MTs and the dislocation of MTs during mitosis.