Effect of colcemid exposure and methanol acetic acid fixation on human metaphase chromosome structure

Abstract

Distribution of human lymphoid cells in the mitotic subphases, prophase, prometaphase, metaphase and anatelophase, was examined, when cells had been cultured and without colcemid exposure. A higher average length of chromosome no. I was found after overnight fixation than after short time fixation with 3:1 methanol acetic acid fixative. The probability of observing banded chromosomes on slides that had not been exposed to any postfixational band induction was higher after overnight fixation than after short time fixation. Since an increase in the extraction of histones caused by the methanol acetic acid fixation of metaphase cells led to an increase of average chromosome length as well as more frequent banding of chromosomes, it is suggested that not only non-histone proteins but also histones are involved in the formation of chromosome bands. In cells harvested without having been exposed to colcemid. most of the observed chromosomes were banded prometaphase chromosomes. It is suggested that the chromosome condensation process, which is delayed or partly inhibited when inhibitors of RNA or protein synthesis are added to the growth medium, continues as long as colcemid exposed cells remain arrested at the meta-anaphase border with free -SH groups available for oxidation.