Ciliate metallothioneins: unique microbial eukaryotic heavy-metal-binder molecules.

This article represents an updated review of ciliate metallothioneins (Tetrahymena species) including a comparative analysis with regard to well-known metallothioneins (MTs) from other organisms and discussion of their exclusive features. It opens with an introduction to ciliates, summarizing the main characteristics of these eukaryotic microorganisms and their use as cellular models to study metallothioneins and metal-eukaryotic cell interactions. It has been experimentally proved that at least three different metal resistance mechanisms exist in ciliates, of which bioaccumulation is the most studied. Structural comparative analysis reveals that Tetrahymena MTs have unique characteristics, such as longer length, a considerably higher cysteine content, different metal-MT stoichiometry values, the presence of new cysteine clusters, and a strictly conserved modular-submodular structure. Gene expression analysis reveals a multistress and differential response to diverse metals and other environmental stressors, which corroborates the classification of these MTs. An in silico analysis of the promoter sequences of some MT genes reveals the presence of conserved motifs that are probably involved in gene expression regulation. We also discuss the great advantages of the first ciliate whole-cell biosensors based on MT promoters from Tetrahymena thermophila to detect heavy metal ions in environmental samples.

MR imaging of the central nervous system in divers.

A group of 70 professional divers and 47 healthy control subjects who had never dived were examined with magnetic resonance (MR) imaging to determine the prevalence of focal white matter changes in the brain. Spots of high signal intensity in white matter on proton density- and/or T2-weighted spin-echo images were detected in 42% of the control subjects and in 34% of the divers. In the control subjects, the prevalence of more than three changes was related to smoking, use of alcohol, head trauma, age of more than 35 years, and a combination of several cerebrovascular risk factors. This relationship was not present in the divers. The prevalence of changes in divers was inversely related to diving depth, amount of diving, participation in "unsafe diving," and decompression sickness. The reasons for these results could not be ascertained. The results are compared with those of MR imaging studies of white matter changes recently presented by other research groups.