Cell cycle behavior of human HP1 subtypes: distinct molecular domains of HP1 are required for their centromeric localization during interphase and metaphase

Abstract

Heterochromatin protein 1 (HP1) plays an important role in heterochromatin formation. Three subtypes of HP1, namely HP1α, β, and γ, have been identified in humans. In this study, using yellow fluorescent protein(YFP) fusion constructs, we examined the intracellular localization of human HP1 subtypes during the cell cycle. During interphase, all three HP1 subtypes were localized to centromeric heterochromatin and to promyelocytic leukemia(PML) nuclear bodies. Different preferences, however, were observed among the subtypes: during interphase HP1β localized most preferentially to centromeric heterochromatin, whereas HP1α and γ were more preferentially localized to PML nuclear bodies. During metaphase, only HP1α, was localized to the centromere. We thus determined which molecular domains of HP1 were necessary for their intracellular localization. Our results showed that the C-terminal fragment (amino acid residues 101-180)of HP1α was necessary for localization to the metaphase centromere and the N-terminal fragment (amino acid residues 1-76) of HP1β was necessary for localization to the interphase centromere. Interestingly, simultaneous observations of residues 101-180 of HP1α and residues 1-76 of HP1βin living HeLa cells revealed that during late prophase, the HP1βfragment dissociated from centromeric regions and the HP1α fragment accumulated in centromeric regions. These results indicate that different specific regions of human HP1α and HP1β mediate localization to metaphase and interphase centromeric regions resulting in association of different subtypes of HP1 with the centromere at different times during the cell cycle.

Drosophila HP1c isoform interacts with the zinc-finger proteins WOC and Relative-of-WOC to regulate gene expression

“…Moreover, ubiquitously expressed HP1 isoforms show differential chromosomal distributions, as HP1a is mainly associated to heterochromatin, while HP1c is excluded from centromeric heterochromatin and HP1b is found both at euchromatic and heterochromatic domains (Smothers and Henikoff 2001). A similar situation is observed in mammals, where the patterns of localiza-tion of the three HP1 isoforms (HP1␣, HP1␤, and HP1␥) overlap only partially and show differential dynamics during differentiation and cell cycle progression (Minc et al 1999;Hayakawa et al 2003;Dialynas et al 2007). On the other hand, in the nematode Caenorhabditis elegans, two HP1 isoforms exist (HPL1 and HPL2), showing preferential euchromatic association, partially nonoverlapping expression and localization patterns, and distinct mutant phenotypes Schott et al 2006).…”

Epigenome and chromatin structure in human embryonic stem cells undergoing differentiation

“…Also intriguing is the dissociation between chromatin condensation and HP1␤ accumulation observed during the early phases of chromatin remodeling caused by nuclear transfer (Martin et al, 2006). Unlike metaphase chromosomes (Minc et al, 1999), HP1␤-abundant chromocenters are restored in somatic cells and in mESCs at G1 phase (Hayakawa et al, 2003;Martin et al, 2006). This is not observed during the G1 phase after nuclear transfer into the oocyte.…”

Dynamic Regulation of Effector Protein Binding to Histone Modifications: The Biology of HP1 Switching

“…Different studies using different cell lines and experimental approaches have shown partial to complete loss of HP1 from mitotic chromatin. [43][44][45][46][47][48] The consensus seems that at this stage of the cell cycle, all of HP1b and HP1g, as well as the majority of HP1a, dissociate from chromatin. Only a fraction of HP1a remains localized at the centromeres.…”