Movement of chromosomes with severed kinetochore microtubules

Experiments from as early as 1966 and thereafter showed that anaphase chromosomes continued to move poleward after their kinetochore microtubules were severed by ultraviolet microbeam irradiation; these conclusions were initially met with skepticism as this contradicted the prevailing view that kinetochore fibre microtubules pulled chromosomes to the pole. However recent experiments using visible-light laser microbeam irradiations have corroborated these earlier experiments as anaphase chromosomes again were shown to move poleward after their kinetochore microtubules were severed. Thus multiple independent studies using different techniques have shown that chromosomes can indeed move poleward without direct microtubule connections to the pole with only a kinetochore ‘stub’ of microtubules. An issue not yet settled is: what propels the disconnected chromosome? There are two not necessarily mutually-exclusive proposals in the literature: (1) chromosome movement is propelled by the kinetochore stub interacting with non-kinetochore microtubules and (2) chromosome movement is propelled by a spindle matrix acting on the stub. In this review we summarize the data indicating that chromosomes can move with severed kinetochore microtubules and we discuss proposed mechanisms of chromosome movement with severed kinetochore microtubules.