We had previously identified the cDNA for a novel protein called osteoblast-specific factor 2 (OSF-2) from an MC3T3-E1 cDNA library using subtraction hybridization and differential screening techniques. Here we describe the localization, regulation, and potential function of this protein. Immunohistochemistry using specific antiserum revealed that in adult mice, the protein is preferentially expressed in periosteum and periodontal ligament, indicating its tissue specificity and a potential role in bone and tooth formation and maintenance of structure. Based on this observation and the fact that other proteins have been called OSF-2, the protein was renamed "periostin." Western blot analysis showed that periostin is a disulfide linked 90 kDa protein secreted by osteoblasts and osteoblast-like cell lines. Nucleotide sequence revealed four periostin transcripts that differ in the length of the C-terminal domain, possibly caused by alternative splicing events. Reverse transcription-polymerase chain reaction analysis revealed that these isoforms are not expressed uniformly but are differentially expressed in various cell lines. Both purified periostin protein and the periostin-Fc recombinant protein supported attachment and spreading of MC3T3-E1 cells, and this effect was impaired by antiperiostin antiserum, suggesting that periostin is involved in cell adhesion. The protein is highly homologous to ig-h3, a molecule induced by transforming growth factor  (TGF-) that promotes the adhesion and spreading of fibroblasts. Because TGF- has dramatic effects on periosteal expansion and the recruitment of osteoblast precursors, this factor was tested for its effects on periostin expression. By Western blot analysis, TGF- increased periostin expression in primary osteoblast cells. Together, these data suggest that periostin may play a role in the recruitment and attachment of osteoblast precursors in the
A photo-hydrogen-evolving molecular device made up of a tris(2,2'-bipyridine)ruthenium(II) derivative and a dichloro(2,2'-bipyridine)platinum(II) derivative has been found to serve as the first effective model of a "molecular device" which evolves molecular hydrogen from water in the presence of a sacrificial electron donor (EDTA), under the visible-light illumination.
Cysts of Azotobacter vinelandii are resting cells that are surrounded by a protective coat, conferring resistance to various chemical and physical agents. The major chemical components of the cyst coat are alkylresorcinols, which are amphiphilic molecules possessing an aromatic ring with a long aliphatic carbon chain. Although alkylresorcinols are widely distributed in bacteria, fungi, plants, and animals, no enzyme systems for their biosynthesis are known. We report here an ars operon in A. vinelandii that is responsible for the biosynthesis of the alkylresorcinols in the cysts. The ars operon consisted of four genes, two of which encoded a type III polyketide synthase, ArsB and ArsC. In vitro experiments revealed that ArsB and ArsC, sharing 71% amino acid sequence identity, were an alkylresorcinol synthase and an alkylpyrone synthase, respectively, indicating that ArsB and ArsC are not isozymes but enzymatically distinct polyketide synthases. In addition, ArsB and ArsC accepted several acyl-CoAs with various lengths of the side chain as a starter substrate and gave corresponding alkylresorcinols and alkylpyrones, respectively, which suggests that the mode of the ring folding is uninfluenced by the structure of the starter substrates. The importance of the alkylresorcinols for encystment was confirmed by gene inactivation experiments; the lack of alkylresorcinols synthesis caused by ars mutations resulted in the formation of severely impaired cysts, as observed by electron microscopy.
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