Thursday, December 1, 2011

Chance Aspects of Cell Fate

Ranging from bacteria to humans, cell fate is generally reached through a hard-wired program. However, in a review on stochasticity and cell fate, Losick and Desplan (p. 65) describe how the surroundings and cell lineage may have a lesser impact on cell fate than normally assumed. Instead, the differentiation pathway may be stochastically or randomly attained. Examples are seen in the entry of Bacillus subtilis into a state of competence or the generation of alternative colorvision photoreceptors in Drosophila melanogaster. There are varied reasons as to why a cell lacks a deterministic program, for example, "bet hedging" in bacteria to anticipate adverse changes in the environment. A stochastic mechanism for cell fate may be advantageous or, in some cases, necessary for the organism's or species survival.

Early Iron Deficit

The timing and processes of the formation of the solar system can be mapped out by measuring long-lived isotopes in meteorites. One such system is 60Fe-60Ni, with a half-life of 1.5 million years; 60Fe only forms in stars. Bizzarro et al. (p. 1178; see the news story by Kerr) find that differentiated meteorites show a very minor deficit of 60Fe compared to Earth, Mars, and chondrites. The authors suggest that the oldest solar system material formed in the absence of 60Fe and that 60Fe was injected into the proto-planetary disk about 1 million years after the solar system formed. This material may have come from a neighboring star, such as a particularly iron-rich supernova.

Acid Buried in Base

Chemists often tailor reaction conditions by manipulating the temperature or acidity of the medium. In contrast, enzymes cannot grossly alter their surroundings, and rely instead on internal cavities that tune the molecular environment of an individual docked substrate. Pluth et al. (p. 85) mimic this strategy using a synthetic cage-like cluster that self-assembles from ligands and metal ions in solution. The electrostatic environment inside the cluster stabilizes cations, and so favors protonation of guest molecules. The cage can function as an acidic enclave in a basic solution and be used to perform acid-catalyzed orthoformate hydrolysis in a surrounding basic medium.