bims-replis 2025-06-15 papers

Cell Rep. 2025 Jun 10. pii: S2211-1247(25)00587-X. [Epub ahead of print]44(6): 115816

Regulation of epigenetics and chromosome structure by human ORC2.

Zhangli Su, Mengxue Tian, Etsuko Shibata, Yoshiyuki Shibata, Tianyi Yang, Zhenjia Wang, Fulai Jin, Chongzhi Zang, Anindya Dutta.

We report a multi-omics study in a human cell line with mutations in three subunits of origin-recognition complex (ORC). Although the ORC subunits should bind DNA as part of a common six-subunit ORC, there are thousands of sites in the genome where one subunit binds but not another. DNA-bound ORC2 compacts chromatin and attracts repressive histone marks to focal areas of the genome, but ORC2 also activates chromatin at many sites and protects the genes from repressive marks. These epigenetic changes regulate hundreds of genes, including some epigenetic regulators, adding an indirect mechanism by which ORC2 regulates epigenetics without local binding. DNA-bound ORC2 also prevents the acquisition of CTCF at focal sites in the genome to regulate chromatin loops and indirectly affect epigenetics. Thus, individual ORC subunits may bind to DNA to act as epigenetic and chromosome structure regulators independent of the role of the six-subunit ORC in DNA replication.

Keywords: CP: Genomics; CP: Molecular biology; CTCF; DNA replication; Hi-C; ORC; epigenetics; gene regulation; genomics; higher-order chromatin organization; histone modifications; origin-recognition complex

DOI: https://doi.org/10.1016/j.celrep.2025.115816

NAR Mol Med. 2025 Apr;2(2): ugaf019

Rare SNP in the HELB gene interferes with RPA interaction and cellular function of HELB.

Bertha Osei, Benjamin H May, Joseph S Beard, Matthew D Thompson, Duah Alkam, Maroof Khan Zafar, Erik Bergstrom, Stephanie D Byrum, Eric J Enemark, Kirk L West, Alicia K Byrd.

HELB is a human helicase involved in initiation of DNA replication, the replication stress response, and regulation of double-strand DNA break repair. rs75770066 is a low-frequency single-nucleotide polymorphism (SNP) in the HELB gene that affects age at natural menopause (ANM). rs75770066 results in a D506G substitution in a HELB-specific motif in the 1A domain of the helicase that contains amino acids known to interact with RPA. We found that this amino acid change has no effect on the enzymatic activity of HELB on naked DNA substrates but reduces the rate of unwinding by HELB on RPA coated substrates, likely because D506G substitution in HELB reduces interaction with RPA. This impaired interaction of D506G HELB with RPA dramatically impairs the cellular function of HELB and likely results in the effects of rs75770066 as this reduces recruitment of HELB to sites of DNA damage. Reduced recruitment of D506G-HELB to double-strand DNA breaks and the concomitant increase in homologous recombination likely alters the levels of meiotic recombination, which affects the viability of gametes. Because menopause occurs when oocyte levels drop below a minimum threshold, altered repair of meiotic double-stranded DNA breaks has the potential to directly affect the ANM.

DOI: https://doi.org/10.1093/narmme/ugaf019

Front Cell Infect Microbiol. 2025 ;15 1584812

Stage-specific MCM protein expression in Trypanosoma cruzi: insights into metacyclogenesis and G1 arrested epimastigotes.

Bruno Alves Santarossa, Évelin Mariani, Artur da Paixão Corrêa, Fernanda C Costa, Martin C Taylor, John M Kelly, Maria Carolina Elias, Simone Guedes Calderano.

Trypanosoma cruzi is a protozoan parasite that is the etiological agent of Chagas disease, which is endemic to Latin America with reported cases in non-endemic regions such as Europe, Asia, and Oceania due to migration. During its lifecycle, T. cruzi alternates between replicative and non-replicative infective lifeforms. Metacyclogenesis is the most studied transition of the T. cruzi life cycle, where replicative epimastigotes differentiate into infective metacyclic trypomastigotes inside the gut of the triatomine vector. This early-branching organism expresses a divergent pre-replication complex (pre-RC) where the only conserved component is the MCM2-7 protein family. Given the role of pre-RC components in cell cycle regulation, we investigated whether MCM expression and location could be involved in proliferation control in epimastigotes and during metacyclogenesis. Using CRISPR/Cas9, we tagged MCM subunits and tracked their expression and subcellular localization. Our findings reveal that MCM subunits are consistently expressed and localized to the nucleus throughout the epimastigote cell cycle, including in G1/G0-arrested cells. However, MCM subunits are degraded during metacyclogenesis as cells enter the G0 state, marking the transition to replication arrest. Therefore, epimastigotes arrested in G1/G0 can either maintain MCM complex expression and resume the cell cycle when conditions become favorable, or they can undergo metacyclogenesis, exiting the cell cycle and entering a G0 state, where MCM subunits are degraded as part of the replication repression mechanism.

Keywords: G0; G1 arrest; MCM; Mini-Chromosome Maintenance; Trypanosoma cruzi; cell cycle arrest; metacyclogenesis; replication control

DOI: https://doi.org/10.3389/fcimb.2025.1584812