RESUMEN
During mitosis, condensin activity is thought to interfere with interphase chromatin structures. To investigate genome folding principles in the absence of chromatin loop extrusion, we codepleted condensin I and condensin II, which triggered mitotic chromosome compartmentalization in ways similar to that in interphase. However, two distinct euchromatic compartments, indistinguishable in interphase, emerged upon condensin loss with different interaction preferences and dependencies on H3K27ac. Constitutive heterochromatin gradually self-aggregated and cocompartmentalized with facultative heterochromatin, contrasting with their separation during interphase. Notably, some cis-regulatory element contacts became apparent even in the absence of CTCF/cohesin-mediated structures. Heterochromatin protein 1 (HP1) proteins, which are thought to partition constitutive heterochromatin, were absent from mitotic chromosomes, suggesting, surprisingly, that constitutive heterochromatin can self-aggregate without HP1. Indeed, in cells traversing from M to G1 phase in the combined absence of HP1α, HP1ß and HP1γ, constitutive heterochromatin compartments are normally re-established. In sum, condensin-deficient mitotic chromosomes illuminate forces of genome compartmentalization not identified in interphase cells.
Asunto(s)
Adenosina Trifosfatasas , Proteínas Cromosómicas no Histona , Proteínas de Unión al ADN , Heterocromatina , Mitosis , Complejos Multiproteicos , Adenosina Trifosfatasas/genética , Adenosina Trifosfatasas/metabolismo , Complejos Multiproteicos/genética , Complejos Multiproteicos/metabolismo , Proteínas de Unión al ADN/metabolismo , Proteínas de Unión al ADN/genética , Mitosis/genética , Humanos , Proteínas Cromosómicas no Histona/metabolismo , Proteínas Cromosómicas no Histona/genética , Heterocromatina/metabolismo , Heterocromatina/genética , Interfase/genética , Cromosomas/genética , Homólogo de la Proteína Chromobox 5 , Cromatina/metabolismo , Cromatina/genéticaRESUMEN
During mitosis, condensin activity interferes with interphase chromatin structures. Here, we generated condensin-free mitotic chromosomes to investigate genome folding principles. Co-depletion of condensin I and II, but neither alone, triggered mitotic chromosome compartmentalization in ways that differ from interphase. Two distinct euchromatic compartments, indistinguishable in interphase, rapidly emerged upon condensin loss with different interaction preferences and dependence on H3K27ac. Constitutive heterochromatin gradually self-aggregated and co-compartmentalized with the facultative heterochromatin, contrasting with their separation during interphase. While topologically associating domains (TADs) and CTCF/cohesin mediated structural loops remained undetectable, cis-regulatory element contacts became apparent, providing an explanation for their quick re-establishment during mitotic exit. HP1 proteins, which are thought to partition constitutive heterochromatin, were absent from mitotic chromosomes, suggesting, surprisingly, that constitutive heterochromatin can self-aggregate without HP1. Indeed, in cells traversing from M- to G1-phase in the combined absence of HP1α, HP1ß and HP1γ, re-established constitutive heterochromatin compartments normally. In sum, "clean-slate" condensing-deficient mitotic chromosomes illuminate mechanisms of genome compartmentalization not revealed in interphase cells.