Yuh H. Nakanishi

A quantitative study on anaphase movement of chromosomes in living grasshopper spermatocytes.

SummaryThe present investigation has been undertaken to obtain data for the analysis of the chromosome movement at anaphase and the formation of a cleavage furrow. The study is based on simultaneous measurements of the spindle and cell diameters as well as of the chromosome separation in living spermatocyte divisions of the grasshoppers, Podisma sapporense and Acrydium japonicum.Evidence from the present investigation shows that the movement of chromosomes to the poles and the elongation of the spindle are separated in time; the spindle length remains unchanged through out anaphase. Spindle elongation is not associated with the separation of daughter chromosomes. The cell, and the spindle as well, elongate after the chromosomes have reached the poles. Cell elongation may follow the stretching of the spindle, and cause sufficient tension to distort the cell wall, resulting in the subsequent formation of a cleavage furrow.

Behavior of the mitochondria in relation to cytoplasmic division in grasshopper spermatocytes.

SummaryThe behavior of the mitochondria was followed in normal and experimentally induced abnormal divisions of grasshopper spermatocytes by phase microscopy, with particular reference to the formation of a cleavage furrow.By acriflavine-treatment the movement of the chromosomes to the poles is inhibited, while the elongation of the mitochondria remains unaffected, and the formation of a cleavage furrow occurs. In benzolor phenol-treated material the chromosomes can move to the poles, while the mitochondria are inhibited from elongating, and the cleavage furrow is not formed at all.From the sequence of events, normal and experimentally induced, the conclusion is possible that there is a close relationship between mitochondrial elongation, cell elongation and cleavage furrow, and that the elongation of the mitochondria induces cell elongation which in turn causes the formation of a cleavage furrow.

Structural changes of deoxyribonucleoprotein fibres following γ-irradiation under aerobic and hypoxic conditions

The DNP fibres γ-irradiated under aerobic condition showed a reduction of their diameter, while no remarkable changes were observed in the DNP fibres irradiated under hypoxic condition by scanning electron microscopy.