Structural evidence for elastic tethers connecting separating chromosomes in crane-fly spermatocytes

Abstract

ABSTRACTDifferent types of anaphase bridges have been reported to form between segregating chromosomes during cell division. Previous studies using laser microsurgery suggested that elastic tethers connect the telomeres of separating anaphase chromosomes in many animal meiotic and mitotic cells. However, structural evidence is lacking for their existence. In this study, we correlated live imaging with electron tomography of crane-fly primary spermatocytes to examine whether visible structures connect separating telomeres in meiosis I. We found structures extending between separating telomeres in all stages of anaphase, from very early anaphase to late anaphase. Ultrastructural analysis revealed that the structures consist of two components: one is darkly stained, looking somewhat like chromatin, whereas the other is more lightly stained, appearing filamentous with internal thinner filaments. While in early anaphase both structures extend between telomeres, in later anaphase the darker structure extends shorter distances from the telomeres but the lighter structure still extends between the separating telomeres. From these observations, we deduced that these structures represent the ‘tethers’ inferred from the laser-cutting experiments in crane-fly spermatocytes. Since the presence of elastic tethers are suggested in a variety of animal cells, they probably are present during anaphase in all animal cells.