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Neuron Sep 2019We performed RNA sequencing on 40,000 cells to create a high-resolution single-cell gene expression atlas of developing human cortex, providing the first single-cell...
We performed RNA sequencing on 40,000 cells to create a high-resolution single-cell gene expression atlas of developing human cortex, providing the first single-cell characterization of previously uncharacterized cell types, including human subplate neurons, comparisons with bulk tissue, and systematic analyses of technical factors. These data permit deconvolution of regulatory networks connecting regulatory elements and transcriptional drivers to single-cell gene expression programs, significantly extending our understanding of human neurogenesis, cortical evolution, and the cellular basis of neuropsychiatric disease. We tie cell-cycle progression with early cell fate decisions during neurogenesis, demonstrating that differentiation occurs on a transcriptomic continuum; rather than only expressing a few transcription factors that drive cell fates, differentiating cells express broad, mixed cell-type transcriptomes before telophase. By mapping neuropsychiatric disease genes to cell types, we implicate dysregulation of specific cell types in ASD, ID, and epilepsy. We developed CoDEx, an online portal to facilitate data access and browsing.
Topics: Autism Spectrum Disorder; Cell Cycle; Cerebral Cortex; Databases, Genetic; Ependymoglial Cells; Epilepsy; Female; Gene Expression Profiling; Gene Expression Regulation, Developmental; Gene Regulatory Networks; Gestational Age; Humans; Intellectual Disability; Interneurons; Neocortex; Neural Stem Cells; Neurogenesis; Neurons; Pregnancy; Pregnancy Trimester, Second; RNA-Seq; Single-Cell Analysis; Telophase
PubMed: 31303374
DOI: 10.1016/j.neuron.2019.06.011 -
Cells Apr 2022A conserved feature of virtually all higher eukaryotes is that the centromeres are embedded in heterochromatin. Here we provide evidence that this tight association... (Review)
Review
A conserved feature of virtually all higher eukaryotes is that the centromeres are embedded in heterochromatin. Here we provide evidence that this tight association between pericentric heterochromatin and the centromere is essential for proper metaphase exit and progression into telophase. Analysis of chromosome rearrangements that separate pericentric heterochromatin and centromeres indicates that they must remain associated in order to balance Cohesin/DNA catenation-based binding forces and centromere-based pulling forces during the metaphase-anaphase transition. In addition, a centromere embedded in heterochromatin facilitates nuclear envelope assembly around the entire complement of segregating chromosomes. Because the nuclear envelope initially forms on pericentric heterochromatin, nuclear envelope formation proceeds from the pole, thus providing time for incorporation of lagging and trailing chromosome arms into the newly formed nucleus. Additional analysis of noncanonical mitoses provides further insights into the functional significance of the tight association between heterochromatin and centromeres.
Topics: Anaphase; Centromere; Heterochromatin; Metaphase; Mitosis
PubMed: 35406810
DOI: 10.3390/cells11071247 -
Archives of Biochemistry and Biophysics Jun 2011At mitosis, cells undergo drastic alterations in morphology and cytoskeletal organization including cell rounding during prophase, mitotic spindle assembly during... (Review)
Review
At mitosis, cells undergo drastic alterations in morphology and cytoskeletal organization including cell rounding during prophase, mitotic spindle assembly during prometaphase and metaphase, chromatid segregation in anaphase, and cytokinesis during telophase. It is well established that myosin II is a motor responsible for cytokinesis. Recent reports have indicated that myosin II is also involved in spindle assembly and karyokinesis. In this review, we summarize current understanding of the functions of myosin II in mitosis and cytokinesis of higher eukaryotes, and discuss the roles of possible upstream molecules that control myosin II in these mitotic events.
Topics: Animals; Cytokinesis; Humans; Mitosis; Myosin Type II; Myosin-Light-Chain Kinase; Myosin-Light-Chain Phosphatase
PubMed: 21396909
DOI: 10.1016/j.abb.2011.03.002 -
Frontiers in Cell and Developmental... 2023Cell division events require regulatory systems to ensure that events happen in a distinct order. The classic view of temporal control of the cell cycle posits that... (Review)
Review
Cell division events require regulatory systems to ensure that events happen in a distinct order. The classic view of temporal control of the cell cycle posits that cells order events by linking them to changes in Cyclin Dependent Kinase (CDK) activities. However, a new paradigm is emerging from studies of anaphase where chromatids separate at the central metaphase plate and then move to opposite poles of the cell. These studies suggest that distinct events are ordered depending upon the location of each chromosome along its journey from the central metaphase plate to the elongated spindle poles. This system is dependent upon a gradient of Aurora B kinase activity that emerges during anaphase and acts as a spatial beacon to control numerous anaphase/telophase events and cytokinesis. Recent studies also suggest that Aurora A kinase activity specifies proximity of chromosomes or proteins to spindle poles during prometaphase. Together these studies argue that a key role for Aurora kinases is to provide spatial information that controls events depending upon the location of chromosomes or proteins along the mitotic spindle.
PubMed: 36994100
DOI: 10.3389/fcell.2023.1139367 -
G3 (Bethesda, Md.) Feb 2021Homoeologous recombination, aneuploidy, and other genetic changes are common in resynthesized allopolyploid Brassica napus. In contrast, the chromosomes of cultivars...
Homoeologous recombination, aneuploidy, and other genetic changes are common in resynthesized allopolyploid Brassica napus. In contrast, the chromosomes of cultivars have long been considered to be meiotically stable. To gain a better understanding of the underlying mechanisms leading to stabilization in the allopolyploid, the behavior of chromosomes during meiosis can be compared by unambiguous chromosome identification between resynthesized and natural B. napus. Compared with natural B. napus, resynthesized lines show high rates of nonhomologous centromere association, homoeologous recombination leading to translocation, homoeologous chromosome replacement, and association and breakage of 45S rDNA loci. In both natural and resynthesized B. napus, we observed low rates of univalents, A-C bivalents, and early sister chromatid separations. Reciprocal homoeologous chromosome exchanges and double reductions were photographed for the first time in meiotic telophase I. Meiotic errors were non-uniformly distributed across the genome in resynthesized B. napus, and in particular homoeologs sharing synteny along their entire length exhibited multivalents at diakinesis and polysomic inheritance at telophase I. Natural B. napus appeared to resolve meiotic errors mainly by suppressing homoeologous pairing, resolving nonhomologous centromere associations and 45S rDNA associations before diakinesis, and reducing homoeologous cross-overs.
Topics: Aneuploidy; Brassica napus; Chromosomes, Plant; Genome, Plant; Meiosis; Polyploidy
PubMed: 33704431
DOI: 10.1093/g3journal/jkaa011 -
International Journal of Molecular... Mar 2021Several lines of evidence suggest the existence in the eukaryotic cells of a tight, yet largely unexplored, connection between DNA replication and sister chromatid... (Review)
Review
Several lines of evidence suggest the existence in the eukaryotic cells of a tight, yet largely unexplored, connection between DNA replication and sister chromatid cohesion. Tethering of newly duplicated chromatids is mediated by cohesin, an evolutionarily conserved hetero-tetrameric protein complex that has a ring-like structure and is believed to encircle DNA. Cohesin is loaded onto chromatin in telophase/G1 and converted into a cohesive state during the subsequent S phase, a process known as cohesion establishment. Many studies have revealed that down-regulation of a number of DNA replication factors gives rise to chromosomal cohesion defects, suggesting that they play critical roles in cohesion establishment. Conversely, loss of cohesin subunits (and/or regulators) has been found to alter DNA replication fork dynamics. A critical step of the cohesion establishment process consists in cohesin acetylation, a modification accomplished by dedicated acetyltransferases that operate at the replication forks. Defects in cohesion establishment give rise to chromosome mis-segregation and aneuploidy, phenotypes frequently observed in pre-cancerous and cancerous cells. Herein, we will review our present knowledge of the molecular mechanisms underlying the functional link between DNA replication and cohesion establishment, a phenomenon that is unique to the eukaryotic organisms.
Topics: Animals; Cell Cycle Proteins; Chromatids; Chromosomal Proteins, Non-Histone; Chromosome Segregation; DNA Replication; G1 Phase; Humans; Telophase; Cohesins
PubMed: 33802105
DOI: 10.3390/ijms22062810 -
Cell Cycle (Georgetown, Tex.) 2014
Topics: Anaphase; Animals; Aurora Kinase B; Chromosome Segregation; Feedback, Physiological; Humans; Nuclear Envelope
PubMed: 25486554
DOI: 10.4161/15384101.2014.959853 -
Nucleus (Austin, Tex.) 2011The nucleolus is a large nuclear domain in which transcription, maturation and assembly of ribosomes take place. In higher eukaryotes, nucleolar organization in three... (Review)
Review
The nucleolus is a large nuclear domain in which transcription, maturation and assembly of ribosomes take place. In higher eukaryotes, nucleolar organization in three sub-domains reflects the compartmentation of the machineries related to active or inactive transcription of the ribosomal DNA, ribosomal RNA processing and assembly with ribosomal proteins of the two (40S and 60S) ribosomal subunits. The assembly of the nucleoli during telophase/early G(1) depends on pre-existing machineries inactivated during prophase (the transcription machinery and RNP processing complexes) and on partially processed 45S rRNAs inherited throughout mitosis. In telophase, the 45S rRNAs nucleate the prenucleolar bodies and order the dynamics of nucleolar assembly. The assembly/disassembly processes of the nucleolus depend on the equilibrium between phosphorylation/dephosphorylation of the transcription machinery and on the RNP processing complexes under the control of the CDK1-cyclin B kinase and PP1 phosphatases. The dynamics of assembly/disassembly of the nucleolus is time and space regulated.
Topics: Animals; Cell Cycle; Cell Nucleolus; Humans; Mitosis; RNA, Ribosomal; Time Factors; Transcription, Genetic
PubMed: 21818412
DOI: 10.4161/nucl.2.3.16246 -
Journal of Cell Science Sep 2021Dephosphorylation of lamin A, which triggers nuclear lamina reconstitution, is crucial for the completion of mitosis. However, the specific phosphatase and regulatory...
Dephosphorylation of lamin A, which triggers nuclear lamina reconstitution, is crucial for the completion of mitosis. However, the specific phosphatase and regulatory mechanism that allow timely lamin A dephosphorylation remain unclear. Here, we report that RepoMan (also known as CDCA2), a regulatory subunit of protein phosphatase 1γ (PP1γ) is transiently modified with SUMO-2 at K762 during late telophase. SUMOylation of RepoMan markedly enhanced its binding affinity with lamin A. Moreover, SUMOylated RepoMan contributes to lamin A recruitment to telophase chromosomes and dephosphorylation of the mitotic lamin A phosphorylation. Expression of a SUMO-2 mutant that has a defective interaction with the SUMO-interacting motif (SIM) resulted in failure of the lamin A and RepoMan association, along with abrogation of lamin A dephosphorylation and subsequent nuclear lamina formation. These findings strongly suggest that RepoMan recruits lamin A through SUMO-SIM interaction. Thus, transient SUMOylation of RepoMan plays an important role in the spatiotemporal regulation of lamin A dephosphorylation and the subsequent nuclear lamina formation at the end of mitosis.
Topics: Lamin Type A; Mitosis; Nuclear Proteins; Sumoylation; Telophase
PubMed: 34387316
DOI: 10.1242/jcs.247171 -
ELife Jul 2021Through membrane sealing and disassembly of spindle microtubules, the Endosomal Sorting Complex Required for Transport-III (ESCRT-III) machinery has emerged as a key...
Through membrane sealing and disassembly of spindle microtubules, the Endosomal Sorting Complex Required for Transport-III (ESCRT-III) machinery has emerged as a key player in the regeneration of a sealed nuclear envelope (NE) during mitotic exit, and in the repair of this organelle during interphase rupture. ESCRT-III assembly at the NE occurs transiently during mitotic (M) exit and is initiated when CHMP7, an ER-localised ESCRT-II/ESCRT-III hybrid protein, interacts with the Inner Nuclear Membrane (INM) protein LEM2. Whilst classical nucleocytoplasmic transport mechanisms have been proposed to separate LEM2 and CHMP7 during interphase, it is unclear how CHMP7 assembly is suppressed in mitosis when NE and ER identities are mixed. Here, we use live cell imaging and protein biochemistry to examine the biology of these proteins during M-exit. Firstly, we show that CHMP7 plays an important role in the dissolution of LEM2 clusters that form at the NE during M-exit. Secondly, we show that CDK1 phosphorylates CHMP7 upon M-entry at Ser3 and Ser441 and that this phosphorylation reduces CHMP7's interaction with LEM2, limiting its assembly during M-phase. We show that spatiotemporal differences in the dephosphorylation of CHMP7 license its assembly at the NE during telophase, but restrict its assembly on the ER at this time. Without CDK1 phosphorylation, CHMP7 undergoes inappropriate assembly in the peripheral ER during M-exit, capturing LEM2 and downstream ESCRT-III components. Lastly, we establish that a microtubule network is dispensable for ESCRT-III assembly at the reforming nuclear envelope. These data identify a key cell-cycle control programme allowing ESCRT-III-dependent nuclear regeneration.
Topics: CDC2 Protein Kinase; Endosomal Sorting Complexes Required for Transport; HeLa Cells; Humans; Membrane Proteins; Microtubules; Mitosis; Nuclear Envelope; Nuclear Proteins; Telophase
PubMed: 34286694
DOI: 10.7554/eLife.59999