Anne Dejean

The progression from the one-cell to the two-cell stage constitutes a remarkable transition, accompanied by the activation of a specific set of embryonic genes, epigenome reprogramming and nuclear architecture reorganization. Some of these characteristics are recapitulated in vitro with the spontaneous emergence of two-cell-like cells from mouse embryonic stem cells, which exhibit a transcriptomic signature resembling the two-cell stage, including the expression of genes such as Dux, Zscan4 and the repetitive element MERVL, as well as a more relaxed chromatin state. Here we show that interchromosomal and intrachromosomal interactions driven by Zscan4 chromatin factors form during this transition and segregate into a distinct genomic compartment, the Z compartment, independently of cohesin and CCCTC-binding factor. Mechanistically, the formation of Z-DNA, an alternative DNA conformation regulated by polyamine levels, appears to promote the emergence of totipotent-like cells and the establishment of the Z compartment. This compartment is characterized by a decrease in active histone marks and a reduced expression of genes associated with differentiation and late developmental processes. Overall, these findings suggest that Z-DNA formation may have a dual role, first in initiating zygotic genome activation (ZGA) and later in guiding genome compartmentalization to safeguard the totipotent-like state by restricting the expression of non-ZGA genes within a permissive chromatin environment.

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive and debilitating muscle disease for which no cure currently exists. In the majority of cases, FSHD is associated with the contraction of the D4Z4 macrosatellite repeat array at the 4q35 locus, leading to the inappropriate activation of DUX4 , normally expressed during early embryogenesis. In FSHD, the genetic contraction is accompanied by hypomethylation of the D4Z4 array. Although a connection between DNA hypomethylation and DUX4 expression has been suggested, the precise mechanisms that regulate DUX4 transcription remain incompletely defined. The post-translational modification by SUMO was shown previously to repress the expression of Dux , the DUX4 homolog, in mouse embryonic stem cells. Based on these findings, we explored here the contribution of SUMOylation in the regulation of DUX4 in human muscle cells. We demonstrate that TAK⍰981 (subasumstat), a selective SUMOylation inhibitor, promotes transcriptional reprogramming of the 4q35 locus and induces DUX4 expression. Importantly, this activation occurs independently of changes in DNA methylation or SMCHD1 ATPase activity. Our findings identify SUMOylation inhibition as a novel regulatory pathway driving DUX4 expression. This work uncovers the importance of SUMOylation in the epigenetic control of the 4q35 locus and DUX4 transcription, providing a potential therapeutic strategy to modulate DUX4 expression in FSHD.

The SUMO pathway mainly functions to repress innate immunity in myeloid cells. Inactivating sumoylation triggers a strong, noncanonical, type I interferon (IFN1) response, amplified and coupled with inflammation upon stimulation. These findings transposed to pre-clinical models with the demonstration that sumoylation inhibitors activate antitumor immunity in an IFN1-dependent manner. Yet, how sumoylation represses immune signaling remains largely unknown. Here, we identified MORC3, a negative regulator of IFNB1, as the top SUMO2/3 substrate in myeloid cells. We show that, in monocytes, SUMO functions to repress basal IFNB1 in cis through a single long tandem repeat regulated by MORC3 [MORC3-regulated element (MRE)] that concentrates multiple motifs for the myeloid-enriched PU.1 factor. Inhibiting sumoylation induces a 3D genome reorganization nucleated from the MRE, which acquires both insulator and PU.1-activated enhancer activities, together with loss of H3.3 and H3K9me3 repressive marks and recruitment of PU.1. Paradoxically, MORC3, that interacts with PU.1, is massively recruited, yet unable to repress the MRE. Finally, we show that both sumoylation and MORC3 ATPase cycle are critical for MORC3 repressive activity. Our study thus uncovers an unconventional mechanism in which sumoylation, in concert with MORC3, orchestrates a metastable H3.3/H3K9me3 heterochromatin state on a multi-PU.1 binding platform to prevent an uncontrolled myeloid-specific immune response.

A remarkable transition during murine development is the progression from the 1-cell embryo to the 2-cell stage, accompanied by the activation of a specific set of embryonic genes, epigenome reprogramming, and nuclear architecture reorganization. Some of these characteristics are recapitulated in vitro with the spontaneous emergence of 2-cell-like cells from mouse embryonic stem cells, which exhibit a transcriptomic signature resembling the 2-cell stage, including the expression of genes such as Dux , Zscan4 , and the repetitive element MERVL , and a more relaxed chromatin state. Here, we show that inter- and intra-chromosomal interactions, driven by Zscan4 chromatin factors, form during this transition and segregate into a distinct genomic compartment (Z compartment). Mechanistically, the formation of Z-DNA, an alternative DNA conformation regulated by polyamine levels, promotes the emergence of totipotent-like cells and the establishment of the Z compartment. This compartment is characterized by a decrease in active histone marks and a reduced expression of genes associated with differentiation and late developmental processes. Overall, these findings suggest that Z-DNA formation may play a dual role, first in activating ZGA genes and later in guiding genome compartmentalization to safeguard the totipotent-like state by restricting the expression of non-ZGA genes within a permissive chromatin environment.

Sumoylation is an essential posttranslational modification in eukaryotes that has emerged as an important pathway in oncogenic processes. Most human cancers display hyperactivated sumoylation and many cancer cells are remarkably sensitive to its inhibition, thus supporting application of chemical sumoylation inhibitors in cancer treatment. Here we show, first, that transformed embryonic fibroblasts derived from mice haploinsufficient for Ubc9, the essential and unique gene encoding the SUMO E2 conjugating enzyme, exhibit enhanced proliferation and transformed phenotypes in vitro and as xenografts ex vivo. To then evaluate the possible impact of loss of one Ubc9 allele in vivo, we used a mouse model of intestinal tumorigenesis. We crossed Ubc9^+/− mice with mice harboring a conditional ablation of Apc either all along the crypt–villus axis or only in Lgr5⁺ crypt-based columnar (CBC) cells, the cell compartment that includes the intestinal stem cells proposed as cells-of-origin of intestinal cancer. While Ubc9^+/− mice display no overt phenotypes and no globally visible hyposumoylation in cells of the small intestine, we found, strikingly, that, upon loss of Apc in both models, Ubc9^+/− mice develop more (>2-fold) intestinal adenomas and show significantly shortened survival. This is accompanied by reduced global sumoylation levels in the polyps, indicating that Ubc9 levels become critical upon oncogenic stress. Moreover, we found that, in normal conditions, Ubc9^+/− mice show a moderate but robust (15%) increase in the number of Lgr5⁺ CBC cells when compared to their wild-type littermates, and further, that these cells display higher degree of stemness and cancer-related and inflammatory gene expression signatures that, altogether, may contribute to enhanced intestinal tumorigenesis. The phenotypes of Ubc9 haploinsufficiency discovered here indicate an unanticipated tumor-suppressive role of sumoylation, one that may have important implications for optimal use of sumoylation inhibitors in the clinic.