Functional analysis of chromosomal proteins and cations on mitotic chromosome structure based on imaging techniques

Abstract

Chromosome condensation is essential for the faithful transmission of genetic information to daughter cells during cell division. However, the chromosome condensation process is still poorly understood. This review discusses the functions of two major factors involved in chromosome condensation, chromosomal proteins and divalent cations. Proteome analysis of the human metaphase chromosome revealed its protein components and identified proteins were functionally calcified. The chromosome scaffold, an axial structure of the chromosome that is composed of several proteins, is important for constructing the X-shaped chromosome morphology. Through conventional fluorescence microscopy, the scaffold structure in a single chromatid has been observed as a single thick axis. However, using super-resolution microscopy and electron microscopy, the scaffold structure was found to be formed of two thin axes. It will generate both stiffness and elasticity to chromosome. Although chromosome structure is severely altered without the scaffold structure, chromosome condensation can also be achieved by divalent cations. Depletion of one of the divalent cations, Ca²⁺, causes defects in mitotic progression and chromosome condensation after the breakdown of the nuclear envelope. Fluorescence lifetime imaging microscopy-Förster resonance energy transfer and electron microscopy experiments demonstrated that chromosome condensation is influenced by Ca²⁺. Ca²⁺ is also required for the stabilization of kinetochore microtubules by loading CENP-F into the kinetochore.