FHA-RING ubiquitin ligases in cell division cycle control

Despite the common occurrence of forkhead associated (FHA) phosphopeptide-binding domains and really interesting new gene (RING) E3 ubiquitin ligase domains, gene products containing both an N-terminal FHA domain and C-terminal RING domain constitute a highly distinctive intersection. Characterized FHA-RING ligases include the two vertebrate proteins, Checkpoint with FHA and RING (Chfr) and RING finger 8 (Rnf8), as well as three fungal proteins, Defective in mitosis (Dma1), Chf1 and Chf2. These FHA-RING ligases play roles in negative regulation of the cell division cycle, apparently by coupling protein phosphorylation events to specific ubiquitylation of target proteins. Here, the available data on upstream and downstream regulation of and by FHA-RING ligases are reviewed. Received 24 April 2008; received after revision 18 June 2008; accepted 20 June 2008     

Rate of sister chromatid exchanges in mammalian cells differing in diploid numbers

Summary The rate of sister chromatid exchanges (SCE) under identical experimental conditions is the same in various mammalian species irrespective of their diploid chromosome numbers.Supported in part by Research grants VC-21 from American Cancer Society and DEB-76-10580 from National Science Foundation.     

Dimethyl sulphoxide effect on division cells

Resumen Dimetil sulfóxido, potente antimetabolito, a distintas concentraciones altera significativamente la cinética de poblaciones meristemáticas radicales deAllium cepa L., produciendo un cuatro de alteraciones morfológicas y figuras mitóticas atípicas.     

Toward an understanding of cell growth and the cell division cycle of unicellular photoautotrophic cyanobacteria

The cell division cycle of Synechococcus sp. strain PCC 6301 in light is characterized by the sequential and orderly appearance of macromolecular synthesis periods. In the dark, macromolecular synthesis and cell division are severely curtailed. When dark-incubated cultures are reexposed to light, a new cell cycle is initiated. The pattern of the cell events displayed by Synechococcus in light and the absence of sustained growth in dark incubation conditions suggests that light-activated regulatory molecules control macromolecular synthesis and the cell division cycle. For example, ribosomal RNA synthesis is stimulated by a light-activated DNA binding factor in light but not in the dark. Light/dark conditions induce cell synchrony in Prochlorococcus. Distinct G1, S and G2 phases characterize cell cycles of marine Synechococcus and Prochlorococcus. Cell division in Synechococcus elongatus PCC 7942 and marine Synechococcus is controlled by circadian oscillators.     

Induction of sister chromatid exchanges in vivo in bone marrow cells of AKR mice]

Induction of sister chromatid exchanges (SCEs) in bone-marrow cells of AKR Mice receiving in vivo four drugs well-known for their mutagenesis activity has been tested. A decreasing activity in SCE was shown by the drugs tested in the order cyclophosphamide, procarbazine, methylmethane sulfonate and diethylnitrosamine. This technique presents an encouraging method for testing the effect of chemical agents in vivo.     

Chromatin assembly during S phase: contributions from histone deposition, DNA replication and the cell division cycle

During S phase of the eukaryotic cell division cycle, newly replicated DNA is rapidly assembled into chromatin. Newly synthesised histones form complexes with chromatin assembly factors, mediating their deposition onto nascent DNA and their assembly into nucleosomes. Chromatin assembly factor 1, CAF-1, is a specialised assembly factor that targets these histones to replicating DNA by association with the replication fork associated protein, proliferating cell nuclear antigen, PCNA. Nucleosomes are further organised into ordered arrays along the DNA by the activity of ATP-dependent chromatin assembly and spacing factors such as ATP-utilising chromatin assembly and remodelling factor ACF. An additional level of controlling chromatin assembly pathways has become apparent by the observation of functional requirements for cyclin-dependent protein kinases, casein kinase II and protein phosphatases. In this review, we will discuss replication-associated histone deposition and nucleosome assembly pathways, and we will focus in particular on how nucleosome assembly is linked to DNA replication and how it may be regulated by the cell cycle control machinery.     

High shortening velocity of isolated single arterial muscle cells

Summary Surprisingly high shortening velocities (<200 msec contraction-relaxation cycles) were found in isolated vascular muscle cells cultured from rat or chick aorta. All of the small fraction of cells with such quick contractions had membrane excitation by short duration spikes, rather than the slower graded depolarization of the other cells which produced 20-fold slower contractions.This research was supported by grant HL16328 from the National Institutes of Health. I wish to thank Aurita Puga and Paige DeCino for their excellent contributions to the cell culture aspects of these experiments.     

High shortening velocity of isolated single arterial muscle cells

Surprisingly high shortening velocities (less than 200 msec contraction-relaxation cycles) were found in isolated vascular muscle cells cultured from rat or chick aorta. All of the small fraction cells with such quick contractions had membrane excitation by short duration spikes, rather than the slower graded depolarization of the other cells which produced 20-fold slower contractions.     

Atypic chronology of the mitotic cycle of neoplastic mouse mast cells

Zusammenfassung Im mitotischen Zyklus vollständig asynchroner, exponentiell proliferierender neoplastischer Manusmastzellen des Stamms P815Y ist dieG1-Phase vollständig abwesend. DNA-Synthese (S-Phase) beansprucht 84%,G2-Phase 14% und Mitose 4% der vollen Dauer des Zell-Zyklus.

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This investigation was supported by the Office of Naval Research under contract No. Nonr-266(76) and by the Health Research Council of the City of New York under contract No. I-428, and carried out at Columbia University (Department of Biochemistry).

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Recipient of Career Scientist Award of the Health Research Council of the City of New York under Contract No. I-428.     

Cell cycle progression by the repression of primary cilia formation in proliferating cells

In most cell types, primary cilia protrude from the cell surface and act as major hubs for cell signaling, cell differentiation, and cell polarity. With the exception of some cells ciliated during cell proliferation, most cells begin to disassemble their primary cilia at cell cycle re-entry. Although the role of primary cilia disassembly on cell cycle progression is still under debate, recent data have emerged to support the idea that primary cilia exert influence on cell cycle progression. In this review, we emphasize a non-mitotic role of Aurora-A not only in the ciliary resorption at cell cycle re-entry but also in continuous suppression of cilia regeneration during cell proliferation. We also summarize recent new findings indicating that forced induction/suppression of primary cilia can affect cell cycle progression, in particular the transition from G0/G1 to S phase. In addition, we speculate how (de)ciliation affects cell cycle progression.     

Observations on division of mitochondria in dedifferentiating cells ofSplachnum ampullaceum (L.) Hedw

Zusammenfassung Während der Dedifferenzierung von Blattzellen des Gametophoren vonSplachnum ampullaceum (L.) Hedw. sind Teilungen von Mitochondrien durch Sprossung beobachtet worden. Mit Hilfe dieses Vorganges bilden sich Mitochondrieninitialen. Auf Grund dieser Beobachtungen wird die Reversibilität der Mitochondrienentwicklung und die Kontinuität von Mitochondrien während der Regeneration wahrscheinlich gemacht.