For many years, mRNA abundance has been used as the surrogate measure of gene expression in biological systems. However, recent genome-scale analyses in both bacteria and eukaryotes have revealed that mRNA levels correlate with steady-state protein abundance for only 50-70% of genes, indicating that translation and post-translation processes also play important roles in determining gene expression. What is not yet clear is whether dynamic processes such as cell cycle progression, differentiation, or response to environmental changes change the relationship between mRNA and protein abundance. Here, we describe a systems approach to interrogate promastigote-to-amastigote differentiation in the obligatory intracellular parasitic protozoan Leishmania donovani. Our results indicate that regulation of mRNA levels plays a major role early in the differentiation process, while translation and post-translational regulation are more important in the latter part. In addition, it appears that the differentiation signal causes a transient global increase in the rate of protein synthesis, which is subsequently down-regulated by phosphorylation of α-subunit of translation initiation factor 2. Thus, Leishmania dynamically changes the relationship between mRNA and protein abundance as it adapts to new environmental circumstances. It is likely that similar mechanisms play a more important role than previously recognized in regulation of gene expression in other organisms.

SummaryThe transcription factor ChAP1 of the fungal pathogen of maize, Cochliobolus heterostrophus, responds to oxidative stress by migration to the nucleus and activation of antioxidant genes. Phenolic and related compounds found naturally in the host also trigger nuclear localization of ChAP1, but only slight upregulation of some antioxidant genes. ChAP1 thus senses phenolic compounds without triggering a strong antioxidant response. We therefore searched for genes whose expression is regulated by phenolic compounds and/or ChAP1. The C. heterostrophus genome contains a cluster of genes for metabolism of phenolics. One such gene, catechol dioxygenase CCHD1, was induced at least 10-fold by caffeic and coumaric acids. At high phenolic concentrations (Ն 1.6 mM), ChAP1 is needed for maximum CCHD1 expression. At micromolar levels of phenolics CCHD1 is as strongly induced in chap1 mutants as in the wild type. The pathogen thus detects phenolics by at least two signalling pathways: one causing nuclear retention of ChAP1, and another triggering induction of CCHD1 expression. The low concentrations required for induction of CCHD1 indicate fungal receptors for plant phenolics. Symbiotic and pathogenic bacteria are known to detect phenolics, and our findings generalize this to a eukaryotic pathogen. Phenolics and related compounds thus provide a ubiquitous plant-derived signal.

The major purpose of this study was a) to identify the types and frequency of caregiving problems and associated stress and coping effectiveness. Secondary purposes were a) to examine changes in problem frequency, stress, and coping effectiveness, over time; and b) to identify relationships between problem stress and personal, illness, coping, and well-being variables. A stress and coping model guided the study. Fifty-eight caregivers participated during the first four months caregiving. Caregiver and stroke survivor demographic and well-being data were collected during acute rehabilitation. Three problem-related themes emerged: interpersonal disruptions (IPD), sustaining the self and family (SS&F), and stroke survivor functioning (SF), Although SS&F problems were most frequent, IPD problems were rated most stressful and lowest in coping effectiveness. A component of emotional distress, either anxiety or depression, was related significantly (p <.05) to the stress level of each problem theme. Counseling on problem solving strategies may improve caregiver well-being.