The psbC start codon in Synechocystis sp. PCC 6803

AbstractThe translation start codon for psbC, the gene encoding CP43, a chlorophyll-binding protein of photosystem II, has been identified for the cyanobacterium Synechosystis sp. PCC 6803 using site-directed mutagenesis. An AUG codon, about 50 bases upstream from the end of psbD-I had previously been assumed to be the translation start site of psbC. However, the fact that the AUG codon is not present in psbC from several other organisms, whereas a GUG codon 14 bases upstream from the end of psbD-I is strictly conserved suggests that CP43 translation starts at the latter codon. Mutation of GUG, but not of AUG, led to a loss of CP43 and photoautotrophic growth, indicating that the GUG codon is the sole initiation site for translation of the CP43 protein in Synechocystis sp. PCC 6803

Mesenchymal Stem Cells from Different Organs are Characterized by Distinct Topographic Hox Codes

Mesenchymal stem cells (MSC) are multipotent cells found as part of the stromal compartment of the bone marrow and in many other organs. They can be identified in vitro as CFU-F (colony forming unit-fibroblast) based on their ability to form adherent colonies of fibroblast-like cells in culture. MSC expanded in vitro retain characteristics appropriate to their tissue of origin. This is reflected in their propensity for differentiating towards specific lineages, and their capacity to generate, upon retransplantation in vivo, a stroma supporting typical lineages of hematopoietic cells. Hox genes encode master regulators of regional specification and organ development in the embryo and are widely expressed in the adult. We investigated whether they could be involved in determining tissue-specific properties of MSC. Hox gene expression profiles of individual CFU-F colonies derived from various organs and anatomical locations were generated, and the relatedness between these profiles was determined using hierarchical cluster analysis. This revealed that CFU-F have characteristic Hox expression signatures that are heterogeneous but highly specific for their anatomical origin. The topographic specificity of these Hox codes is maintained during differentiation, suggesting that they are an intrinsic property of MSC. Analysis of Hox codes of CFU-F from vertebral bone marrow suggests that MSC originate over a large part of the anterioposterior axis, but may not originate from prevertebral mesenchyme. These data are consistent with a role for Hox proteins in specifying cellular identity of MSC