Initiation Of New Cycles Research Articles

A Rab39-Klp98A-Rab35 endocytic recycling pathway is essential for rapid Golgi-dependent furrow ingression.

Ingression of the plasma membrane is an essential part of the cell topology-distorting repertoire and a key element in animal cell cytokinesis. Many embryos have rapid cleavage stages in which they are furrowing powerhouses, quickly forming and disassembling cleavage furrows on timescales of just minutes. Previous work has shown that cytoskeletal proteins and membrane trafficking coordinate to drive furrow ingression, but where these membrane stores are derived from and how they are directed to furrowing processes has been less clear. Here, we identify an extensive Rab35/Rab4>Rab39/Klp98A>trans-Golgi network (TGN) endocytic recycling pathway necessary for fast furrow ingression in the Drosophila embryo. Rab39 is present in vesiculotubular compartments at the TGN where it receives endocytically derived cargo through a Rab35/Rab4-dependent pathway. A Kinesin-3 family member, Klp98A, drives the movements and tubulation activities of Rab39, and disruption of this Rab39-Klp98A-Rab35 pathway causes deep furrow ingression defects and genomic instability. These data suggest that an endocytic recycling pathway rapidly remobilizes membrane cargo from the cell surface and directs it to the trans-Golgi network to permit the initiation of new cycles of cleavage furrow formation.

Identifying and Characterizing Cyclicality and Seasonality in Environmental Data with An Adaptive Filter Implementation of A Phase Locked Loop

Phase Locked Loops are provided as a manner of assessing, monitoring and forecasting with seasonal or cyclical data. Phase Locked Loops using adaptive filtering were initially utilized for gravitational wave data analysis. In this paper we examine this implementation as an alternative approach for identifying the presence of one or more cycles in environmental data. Unlike most techniques for assessing seasonality phase lock loops can identify the presence of cycles without prior suspicion of their nature and existence. This is important for identifying either the initiation of new cycles or changes in existing cycles. As environmental data can be impacted by the presence of numerous cyclical phenomena and these cycles can change over time, this is a suitable and valuable technique. The technique can be used on existing data sets or assessing data streams. Phase Locked Loops are advantageous over many currently as the presence of multiple different cycles can be identified without prior suspicion and specification of the nature of the cyclicality of the data. The speed and parsimonious nature of the technique makes Phase Lock Loops ideal for Big Data and data flows that are so large that they must be assessed on a real time basis. The technique can manage and advise of changes in frequency, amplitude and phase shifts. The technique is illustrated utilizing weather data.

Preventing diversification of malignant tumor cells during therapy.

One of the most difficult problems arising during cancer therapy is the emergence of unique tumor cell subpopulations that express altered malignant and therapeutic properties. In model tumor systems cytotoxic therapies that eliminate all but a few tumor cells seem to stimulate cell diversification to yield heterogeneous cell populations with divergent properties. Clinically the use of repeated cycles of cytotoxic therapies followed by intervening recovery periods often results in the eventual emergence of highly resistant and increasingly malignant tumor cells. To circumvent tumor cell diversification during therapeutic recovery periods we suggest that cytostatic agents might be employed. Although cytostatic agents such as differentiation modulators, hormones, growth factors, vitamins, and other natural products are unlikely to be effective therapeutic agents if used alone, they could be used during therapeutic recovery periods to modulate the diversification of surviving tumor cells so that these periods might be characterized by less extensive tumor cell diversification. At the end of recovery periods after the removal of cytostatic agents, surviving tumor cells could be briefly restimulated by growth factors, hormones or mitogens, just prior to initiation of new cycles of therapy using cytotoxic agents.

Protein synthesis and the arrest of bacterial DNA synthesis by bacteriophage ∅X174

Bacterial DNA synthesis is totally arrested 12–15 min after ∅X infection at 40°, while the synthesis of RNA, protein, and phage single-stranded DNA continue. Chloramphenicol (30 μg/ml) prevents such inhibition: host DNA synthesis persists, including the initiation of new cycles of replication. This effect is observed only at low multiplicities of infection (3–5). At higher multiplicities, it is obscured by an immediate general impairment of macromolecular synthesis, which is not prevented by chloramphenicol. The specific arrest of host DNA synthesis requires protein synthesis at two stages of the latent period. Chloramphenicol added 10 min after infection interferes with the arrest, whereas its later addition does not. Thus the arrest is dependent on protein whose synthesis begins at about 10 min. Furthermore, protein synthesis is also required before this, for chloramphenicol prohibits some essential step which normally takes place during the delay before the arrest. The identities of the proteins involved are unknown. Experiments with appropriate phage mutants show that the arrest occurs normally in cells infected with strains unable to replicate the two-stranded “replicative form” of the phage DNA or synthesize progeny single-stranded DNA.

Initiation of DNA replication cycles in Escherichia coli following DNA synthesis inhibition

The pattern of initiation of new growing points in the bacterial chromosome has been studied in a temperature-sensitive DNA replication-deficient mutant of Escherichia coli, strain TAU-bar t3. In particular, the effect of a period at the restrictive temperature upon this pattern has been examined. Selected regions of the chromosome were marked by radioisotopic labeling in cultures synchronized by amino acid starvation. The subsequent pattern of DNA replication was determined by equilibrium sedimentation of isolated DNA in a CsCl density gradient after a period of DNA synthesis in the presence of 5-bromouracil. The relative amount of label in the hybrid 5-bromouracil DNA band indicated the replication of the marked regions. New growing points were preferentially initiated at the chromosomal origin, as defined by amino acid starvation, following a period of DNA synthesis inhibition. A period of inhibition obtained by placing the mutant at the restrictive temperature had the identical effect to that of a period of thymine starvation upon the subsequent premature initiation of new replication cycles. Our results support the hypothesis that the initiation of new cycles is independent of the presence or locations of existing points of replication and that it is dependent entirely upon cytoplasmic factors, such as protein synthesis and possibly membrane synthesis.

DNA synthesis in Lactobacillus acidophilus in the absence of RNA and protein synthesis: a study with rifampicin.

Synthesis of DNA in Lactobacillus acidophilus R-26 was investigated in the presence of rifampicin which inhibits RNA and protein synthesis. Increments in DNA of between 140 and 200% were found under these conditions. Indirect evidence is presented that these large increments are not due to the presence of several replication points in the bacterial chromosome at the time of addition of the drug. Incubation with rifampicin was found to result in a progressive decrease in the capacity for DNA synthesis. This decrease was independent of the amount of DNA synthesized during incubation with rifampicin but was dependent on the time of incubation in the presence of the drug. It is proposed that inhibition of protein and RNA synthesis in L. acidophilus does not inhibit initiation of new cycles of chromosome replication but results in a progressive loss of the capacity to replicate DNA.

Chromosome transfer and the DNA replication cycle in [formula omitted], [formula omitted

Phenethyl alcohol (PEA) has been employed as an inhibitor of DNA synthesis in order to elucidate the relationship between the synthesis of DNA in Hfr strains of Escherichia , coli and the transfer of chromosomal markers during conjugation ( Bouck and Adelberg, 1963; and Jacob, Brenner, and Cuzin, 1963). Treick and Konetzka (1964) have shown recently that PEA inhibits the initiation of new cycles of DNA replication in E . coli but permits the completion of those cycles initiated before addition of PEA to the medium. Therefore, cycles of DNA replication can be controlled by the addition, removal, and readdition of PEA to a culture at specific time intervals. The relationship of the DNA replication cycle to the ability of the Hfr to transfer chromosomal markers constitutes the subject of this investigation.