Compartmentalization of HP1 Proteins in Pluripotency Acquisition and Maintenance

• Published in: Stem cell reports 2018-02, Vol.10 (2), p.627-641
• Main Authors: Zaidan, Nur Zafirah, Walker, Kolin J., Brown, Jaime E., Schaffer, Leah V., Scalf, Mark, Shortreed, Michael R., Iyer, Gopal, Smith, Lloyd M., Sridharan, Rupa
• Format: Article
• Language: English
• Subjects: Animals; Cellular Reprogramming - genetics; Chromatin - chemistry; Chromatin - genetics; Chromosomal Proteins, Non-Histone - chemistry; Chromosomal Proteins, Non-Histone - genetics; Dppa4; Endopeptidases - chemistry; Endopeptidases - genetics; Exoribonucleases; H3.3; H3K9M; Histone-Lysine N-Methyltransferase - chemistry; Histone-Lysine N-Methyltransferase - genetics; Histones - genetics; HP1α knockout; HP1β knockout; HP1γ knockout; Humans; Induced Pluripotent Stem Cells - chemistry; Induced Pluripotent Stem Cells - cytology; iPSC; Mice; Mice, Knockout; Multiprotein Complexes - chemistry; Multiprotein Complexes - genetics; Nuclear Proteins - genetics; Octamer Transcription Factor-3 - chemistry; Octamer Transcription Factor-3 - genetics; pluripotency; Proteins - chemistry; Proteins - genetics; Repressor Proteins; reprogramming; Resource; Ribonucleases; Senp7; Transcription Factors
• ISSN: 2213-6711; 2213-6711
• DOI: 10.1016/j.stemcr.2017.12.016

The heterochromatin protein 1 (HP1) family is involved in various functions with maintenance of chromatin structure. During murine somatic cell reprogramming, we find that early depletion of HP1γ reduces the generation of induced pluripotent stem cells, while late depletion enhances the process, with a concomitant change from a centromeric to nucleoplasmic localization and elongation-associated histone H3.3 enrichment. Depletion of heterochromatin anchoring protein SENP7 increased reprogramming efficiency to a similar extent as HP1γ, indicating the importance of HP1γ release from chromatin for pluripotency acquisition. HP1γ interacted with OCT4 and DPPA4 in HP1α and HP1β knockouts and in H3K9 methylation depleted H3K9M embryonic stem cell (ESC) lines. HP1α and HP1γ complexes in ESCs differed in association with histones, the histone chaperone CAF1 complex, and specific components of chromatin-modifying complexes such as DPY30, implying distinct functional contributions. Taken together, our results reveal the complex contribution of the HP1 proteins to pluripotency. •Release of HP1γ from anchoring by Senp7 increases reprogramming efficiency•HP1γ switches enrichment from histone H1 to histone H3.3 in pluripotent cells•HP1γ interacts with OCT4 and DPPA4 independent of HP1α, HP1β, and H3K9 methylation•Proteomic characterization of HP1 protein family in pluripotent cells In this article, Sridharan and colleagues perform proteomic characterization of the heterochromatin protein 1 (HP1) family in reprogramming and pluripotency. Depletion of HP1γ or its interacting partner SENP7, which anchors it to heterochromatin, increased iPSC generation. In pluripotent cells, HP1γ is highly nucleoplasmic and enriched with histone H3.3. HP1γ interacts with OCT4 and DPPA4 independent of HP1α, HP1β, and H3K9 methylation. HP1α and HP1γ differ in association with specific components of chromatin-modifying complexes such as DPY30.