Building mitotic chromosomes

Abstract

Mitotic chromosomes are the iconic structures into which the genome is packaged to ensure its accurate segregation during mitosis. Although they have appeared on countless journal cover illustrations, there remains no consensus on how the chromatin fiber is packaged during mitosis. In fact, work in recent years has both added to existing controversies and sparked new ones. By contrast, there has been very significant progress in determining the protein composition of isolated mitotic chromosomes. Here, we discuss recent studies of chromosome organization and provide an in depth description of the latest proteomics studies, which have at last provided us with a definitive proteome for vertebrate chromosomes.

Figure 1

Functional subdomains in mitotic chromosomes (a), include, (b) Centromeres, Telomeres, (c) the Chromosome periphery and (d) chromosome arms. (e) The 9 classes of proteins found in chromosomes. (f) Estimated percentages of total chromosomal protein mass in the major classes of proteins [32^••].

Figure 2

Combining classifiers in 3-dimensions increases specificity. In this case the axes plot Enrichment (ratio of each protein in chromosomes versus that in an equal protein mass of cytoplasm) versus SMC2 dependency (amount of each protein in wild type chromosomes divided by its amount in chromosomes from SMC2-depleted cells) versus the Combined random forest score (calculated by combining all proteomic classifiers with nearest neighbor analysis and quantitative bioinformatic analysis of protein domains) [32^••]. Core histones and condensin subunits cluster in the analysis.