Previous studies of the avian reovirus strain S1133 (ARV-S1133) S1 genome segment revealed that the open reading frame (ORF) encoding the C viral cell attachment protein initiates over 600 nucleotides distal from the 5 end of the S1 mRNA and is preceded by two predicted small nonoverlapping ORFs. To more clearly define the translational properties of this unusual polycistronic RNA, we pursued a comparative analysis of the S1 genome segment of the related Nelson Bay reovirus (NBV). Sequence analysis indicated that the 3-proximal ORF present on the NBV S1 genome segment also encodes a C homolog, as evidenced by the presence of an extended N-terminal heptad repeat characteristic of the coiled-coil region common to the cell attachment proteins of reoviruses. Most importantly, the NBV S1 genome segment contains two conserved ORFs upstream of the C coding region that are extended relative to the predicted ORFs of ARV-S1133 and are arranged in a sequential, partially overlapping fashion. Sequence analysis of the S1 genome segments of two additional strains of ARV indicated a similar overlapping tricistronic gene arrangement as predicted for the NBV S1 genome segment. Expression analysis of the ARV S1 genome segment indicated that all three ORFs are functional in vitro and in virus-infected cells. In addition to the previously described p10 and C gene products, the S1 genome segment encodes from the central ORF a 17-kDa basic protein (p17) of no known function. Optimizing the translation start site of the ARV p10 ORF lead to an approximately 15-fold increase in p10 expression with little or no effect on translation of the downstream C ORF. These results suggest that translation initiation complexes can bypass over 600 nucleotides and two functional overlapping upstream ORFs in order to access the distal C start site.The orthoreoviruses consist of a number of diverse virus species, all of which have a similar capsid structure and a genome composed of 10 double-stranded RNA (dsRNA) segments (38). For the most part, the genome segments of reoviruses are monocistronic, each encoding a single unique polypeptide. The mammalian reovirus (MRV) S1 genome segment, however, is bicistronic and encodes two unrelated polypeptides from overlapping open reading frames (ORFs). The 1 viral cell attachment protein is encoded by a large ORF that originates near the 5Ј end of the mRNA and spans almost the complete length of the S1 mRNA (12, 37). A second small ORF, beginning at nucleotide position 71, is nested within the 1 ORF in a ϩ1 reading frame and encodes the small nonstructural 1NS protein of MRV (14,23).Since the translation start site for 1 is in a nonpreferred context (a pyrimidine at position Ϫ3), leaky scanning by the preinitiation complex most likely accounts for translation of the downstream 1NS ORF from the MRV S1 mRNA (28). In addition to leaky scanning, there is evidence suggesting that translation of the 1 protein from the bicistronic S1 mRNA is modulated by ribosomal pausing at the downstream 1NS start site (7, 15).As wit...

To date, mesenchymal stem cells (MSCs) from various tissues have been reported, but the yield and differentiation potential of different tissue-derived MSCs is still not clear. This study was undertaken in an attempt to investigate the multilineage stem cell potential of bone and cartilage explant cultures in comparison with bone marrow derived mesenchymal stem cells (BMSCs). The results showed that the surface antigen expression of tissue-derived cells was consistent with that of mesenchymal stem cells, such as lacking the hematopoietic and common leukocyte markers (CD34, CD45) while expressing markers related to adhesion (CD29, CD166) and stem cells (CD90, CD105). The tissue-derived cells were able to differentiate into osteoblast, chondrocyte and adipocyte lineage pathways when stimulated in the appropriate differentiating conditions. However, compared with BMSCs, tissue-derived cells showed less capacity for multilineage differentiation when the level of differentiation was assessed in monolayer culture by analysing the expression of tissuespecific genes by reverse transcription polymerase chain reaction (RT-PCR) and histology. In high density pellet cultures, tissue-derived cells were able to differentiate into chondrocytes, expressing chondrocyte markers such as proteoglycans, type II collagen and aggrecan. Taken together, these results indicate that cells derived from tissue explant cultures reserved certain degree of differentiation properties of MSCs in vitro.

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