Project description:Faithful meiotic segregation requires pairwise alignment of the homologous chromosomes and Synaptonemal Complex assembly (SC) at their interface. Here, we investigate on new factors that promote and coordinate these events during C. elegans meiosis. We identify BRA-2 (BMP Receptor Associated family member 2) as an interactor of HIM-17, previously shown to promote double-strand break formation. We found that loss of bra-2 specifically impairs synapsis licensing without affecting homologs recognition, SC maintenance or chromosome movement. Double mutant analysis revealed a previously unrecognized role for HIM-17 in promoting homolog pairing under dysfunctional SC assembly, without perturbing nuclear envelope recruitment of factors required for chromosome movement. We provide evidence that bra-2 and him-17 act in distinct pathways, exerting partially redundant functions in SC licensing, as well as separable roles in regulating homologs pairing. Altogether, our findings unveil novel mechanisms that ensure stabilization of homologous chromosome interaction via SC licensing upon homology assessment.
Project description:Cell proliferation is tightly controlled by inhibitors that block cell cycle progression until growth signals relieve this inhibition, allowing cells to divide. In several tissues including the liver, cell proliferation is inhibited at mitosis by the transcriptional repressors E2F7 and E2F8, leading to formation of polyploid cells. Whether growth factors promote mitosis and cell cycle progression by relieving the E2F7/E2F8-mediated inhibition is unknown. We report here on a new mechanism of cell division control in the postnatal liver, in which Wnt/βcatenin signaling maintains active hepatocyte cell division through Tbx3, a Wnt target gene. Tbx3 directly represses transcription of E2F7 and E2F8, thereby promoting mitosis. This cascade of sequential transcriptional repressors, initiated by Wnt signals, provides a new paradigm for exploring how commonly active developmental signals impact cell cycle completion.
Project description:Unlike other bacteria, cell growth in rhizobiales is unipolar and asymmetric. The regulation of cell division, and its coordination with metabolic processes is an active field of research. In Rhizobium etli, gene RHE_PE00024, located in a secondary chromosome, is essential for growth. This gene encodes a hybrid histidine kinase sensor protein, participating in a, as yet undescribed, two-component signaling system. In this work, we show that a conditional knockdown mutant (cKD24) in RHE_PE00024 (hereby referred as rdsA, after rhizobium division and shape) generates a striking phenotype, characterized by cells with a round shape, with stochastic and uncoordinated cell division. A fraction of the cells showed also multiple ectopic polar growths, sometimes leading to growth from the old pole, a sector that is normally inactive for growth in a wild-type cell. Homodimerization of RdsA appears to be required for normal function. RNAseq analysis of mutant cKD24 reveals global changes, with differentially expressed genes in at least five biological processes: cell division, wall biogenesis, respiration, translation, and motility. These modifications may affect proper structuring of the divisome, as well as peptidoglycan synthesis. Together, these results indicate that the hybrid histidine kinase RdsA is an essential global regulator influencing cell division and cell shape in R. etli.
Project description:RecBCD protein complex is an important player of DSB repair in bacteria and bacteria that cannot repair DNA double-stranded breaks (DSB) have a low viability. Whole genome sequencing analyses showed a deficit in specific sequences of the chromosome terminus region in recB mutant cells, suggesting terminus DNA degradation during growth. We studied here the phenomenon of terminus DNA loss by 42 whole genome sequencing and microscopy analyses of exponentially growing bacteria. We tested all processes known to take place in the chromosome terminus region for a putative role in DNA loss: replication fork termination, dimer resolution, resolution of catenated chromosomes, and translocation of the chromosome arms in daughter cells during septum formation. None of the mutations that affect these processes prevents the phenomenon. However, we observed that terminus DNA loss is abolished in cells that cannot divide. We propose that in cells defective for RecBCD-mediated DSB repair the terminus region of the chromosome remains in the way of the growing septum during cell division, then septum closure triggers chromosome breakage and, in turn, DNA degradation.
Project description:Regulation of cell division in archaea: the small protein CdrS promotes cell division and controls multiple genes in Haloferax volcanii
Project description:Regulation of cell division in archaea: the small protein CdrS promotes cell division and controls multiple genes in Haloferax volcanii
Project description:Chromosome congression, a process of chromosome alignment at the spindle equator, is a key step in cell division. While much work has addressed the role of protein networks in controlling cell division, we have very little understanding how long noncoding RNAs (lncRNAs) and RNA binding proteins (RBPs) contribute to the fidelity of cell division. To investigate the role of lncRNA C1QTNF1-AS1 and its interacting protein partner RSRC2 in cell division, we depleted C1QTNF1-AS1 and RSRC2 with LNA gapmers and siRNAs, respectively, in HCT116 cells and analysed their impact on gene expression and splicing alterations.
Project description:During meiosis, chromosomes undergo extensive changes in structure and intranuclear positioning. How these chromosome organization changes occur and how they influence meiosis-specific chromosome events are not fully understood. Using Hi-C, we characterized chromosome architecture throughout mouse spermatogenesis at high temporal resolution. Our study revealed an intimate link between chromosome organization features and homolog pairing and alignment. We found that the meiotic chromosomes progressively reshape from TAD-like domains into linearly arranged loop arrays during prophase I. The transcriptionally active and inactive genomic regions exhibit distinct dynamics of loop growth, resulting in alternating domains consisting of shorter and longer chromosome loops. Such a domanial organization along meiotic chromosome axes is tightly correlated with the strength and precision of inter-homolog alignment. We further showed that a significant fraction of chromosomes near chromosome ends exhibit elevated inter-chromosomal association upon entering zygotene stage, while also exhibiting a higher degree of inter-homolog alignment. Using a mouse model defective in LINC complex component SUN1, we demonstrated that the prominent alignment of chromosome ends is dependent on the association of telomeres with the mechano-transducing LINC complex, but not the tethering of telomeres to the nuclear periphery. Taken together, our results suggest the 3D chromosome organization may provide a structural framework for the regulation of meiotic chromosome processes in higher eukaryotes.