Circadian Oscillator

Structural Insights into a Circadian Oscillator
Science 31 October 2008 p697

This particular piece concerns the structures and components by which cells keep time. It is not necessarily time as much as rhythmic milestones.

Endogenous (produced from growth of deep tissue) circadian system in cyanobacteria control processes. A circadian rhythm is by definition endogendous and refers to a roughly 24 hour cycle. This machinery can be reconstructed just with proteins KaiA, KaiB, and KaiC. They work through conformational changes and phosphorylation (of what). The mechanism can be deduced as a racheting mechanism and ticks unidirectionally.

Biological processes are dictated by daily, self-sustaining circadian clocks of 24 hour cycles. They show a difference for day and night mediated by dark and light cycles to phase with the environment.

The study concerned prokaryotic cyanobacterium Synechoccus elongates. The rhythm conforms optimally to the daily cycle, including photosynthesis, nitrogen fixation, and gene expression.

This study used competition assays that are…

Any competition assay takes advantage of the fact that that some
signal you can measure depends on the _total_ concentration of
substance. Thus, by introducing a range of _known_ amounts of that
substance and therefore _diluting_ the same substance present in the
sample at unknown concentration, one can extract the number in the
sample.

that demostrate that this clock system significantly enhanced the fitness of the cells in rhythmic environments, but not in non-selective environments.

Clocks have been seen to influence:
- the topology of the entire cyanobacterial chromosome
- the superhelical status of DNA, such as large scale torsion that modulates transcription rates. Therefore, gene-expression patterns are mediated by caily changes in the topology of the gene.
- The chromosome might be envisioned as an oscillating nucleoid that regulates all promoter.
- KaiABC controls the phosphorylation status of RpaA that is a down transcriptional regulator. This is the SasA/RpaA two-component system mediating signals from KaiABC.

Thioredoxin- Thioredoxins are proteins that act as antioxidants by facilitating the reduction of other proteins by cysteine thiol-disulfide exchange.

Phosporylation occurs on the serine and theronine.

Triclosan

Triclosan is the most common chemical in antibacterial products. Genetic mutations can arise in bacteria exposed to triclosan. Triclosan and its close chemical relative triclocarban have been found in 60% of US streams and rivers (Rolf Halden-John Hopkins Bloomberg School of Public Health). Triclosan has been found in human breast milk and blood plasma. It can comprise the hormone system. Scientific American Februaru 200 8 page 96.Triclosan is alcohol soluable and is comprised of phenols, which have antibacterial properties. It is a biocide, with cytoplasm and membrane targets.

Neutrophil Follow-up

There are three types of white blood cells: Granulocytes, Monocytes, and Lymphocytes. 

Neutrophils are a type of granulocyte that is also called polymorphonuclear leucocyte. They are the most common. They phagocytose and destroy microorganisms -especially bacteria. 

The other types of granulocytes are the basophil - that secrete histamine and mediate inflammatory reactions and eosinophils that destroy parasites.

Monocytes mature into macrophages. Macrophages and Neutrophils make up the main phagocytes in the body.

Neutrophil Soldiers or Trojan Horses?

Science 

15 August 2008

p917

We know that biting insects transmits viral, bacterial, and parasitic infections. We do not know the initial events that occur as pathogens are introduced by these vectors into the wounds. It is under investigation that early events in vector mediated injury influence the outcome of sandfly-transmitted parasite Leishmania major. 

Neutrophils are the first wave of inflammatory cells that migrate into these sites. They have phagocytic actions are regarded as foot solders armed with oxygen radicals, lytic enzymes, and cationic proteins. Unfortunetly, they are short lived. Their corpes are phagocytosed by macrophages. L. major internalizes by entering neurophils and become phagocytosed. 

This was possible with transgenic mice with fluorescent neutrophils and deep tissue immaging. 

Was the phagocytic events independent of sand fly bite and L. major internalization? Yes, because they discovered that by injecting beads, a similar accumulation event of neutrophils occured. 

Does any interfere with neutrophils accumulate?  Tissue damage was proposed as an alternative that overrid the effect of sandfly bite. But sustained recruitment was observed compared with less from just a needle stick. 

Most cells that contained L. major were neutrophils after 18 hours. (So there was a time dependance)

and soon after most cells that had L. major were macrophages in 6 to seven days. 

What was unexpected was that instead of engulfing dying infected neutrophils, macrophages acquired the parasites that had been released from neutrophils undergoing apoptosis. 

BUT, macrophages were not predominant, others were: interleukin-1. Since there was an absence of neutrophils, it hindered the ability to infect macrophages. 

An alternative mechanism is that parasites are better adapted to survive in macrophages. (?)

Dendritic cells and Langerhans cells are important to transport the parasite to lymph nodes. 

Most parasites die in the neutrophil by oxidative burst. 

The Trojan Horse theory is also applicable to Ehrlichia and Francisella tularensis.

Beena John and Christopher A. Hunter

University of Pennsylvania Vet Med

What I Learned

Infections can have a model of entry

The Trojan Horse Theory - Immune cells can care infection

Because something happens (neutrophil recruitment) it might not lead to the next step (macrophage recruitment). Paradoxically, it leads to other recruitment but a less infection. 

Just because something should do something (phagocytose) it might not.

What are the Questions I Learned

Every Step needs another explaination. Neutrophils accumlate at wound site, infection or not. 

What interfers with accumlation? Possible tissue damage.

What are the things that can hinder the steps?