A Novel Gene, fudoh, in the SCCmec Region Suppresses the Colony Spreading Ability and Virulence of Staphylococcus aureus

Staphylococcus aureus colonies can spread on soft agar plates. We compared colony spreading of clinically isolated methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). All MSSA strains showed colony spreading, but most MRSA strains (73%) carrying SCCmec type-II showed little colony spreading. Deletion of the entire SCCmec type-II region from these MRSA strains restored colony spreading. Introduction of a novel gene, fudoh, carried by SCCmec type-II into Newman strain suppressed colony spreading. MRSA strains with high spreading ability (27%) had no fudoh or a point-mutated fudoh that did not suppress colony spreading. The fudoh-transformed Newman strain had decreased exotoxin production and attenuated virulence in mice. Most community-acquired MRSA strains carried SCCmec type-IV, which does not include fudoh, and showed high colony spreading ability. These findings suggest that fudoh in the SCCmec type-II region suppresses colony spreading and exotoxin production, and is involved in S. aureus pathogenesis

Heavy-ion-induced mutations in the gpt delta transgenic mouse: Effect of p53 gene knockout

The influence of the loss of p53 gene on heavy-ion-induced mutations was examined by constructing a new line of transgenic mice, p53 knockout (p53-/-) gpt delta. In this mouse model, deletions in lambda DNA integrated into the mouse genome are preferentially selected as Spi- phages, which can then be subjected to molecular analysis. Mice were exposed to 10 Gy of whole-body carbon-ion irradiation. The carbon ions were accelerated to 135 MeV/u by the RIKEN Ring Cyclotron. The p53 defect markedly enhanced the Spi- mutant frequency (MF) in the kidneys of mice exposed to C-ion irradiation: the Spi- MF increased 4.4- and 2.8-fold over the background level after irradiation in p53-/- and p53+/+ mice, respectively. There was no significant difference in the background Spi- MF between p53-/- and p53+/+ mice. Sequence analysis of the Spi- mutants indicated that the enhancement of kidney Spi- MF in p53-/- mice was primarily due to an increase in complex or rearranged-type deletions. In contrast to the kidney, the p53 defect had no effect on the Spi- MF in liver: Spi- MF increased 3.0- and 2.7-fold after the irradiation in p53-/- and p53+/+ mice, respectively. Our results suggest that p53 suppresses deletion mutations induced by heavy-ion irradiation in an organ-specific manner

Osteogenic Differentiation Capacity of Human Skeletal Muscle-Derived Progenitor Cells

<div><p>Heterotopic ossification (HO) is defined as the formation of ectopic bone in soft tissue outside the skeletal tissue. HO is thought to result from aberrant differentiation of osteogenic progenitors within skeletal muscle. However, the precise origin of HO is still unclear. Skeletal muscle contains two kinds of progenitor cells, myogenic progenitors and mesenchymal progenitors. Myogenic and mesenchymal progenitors in human skeletal muscle can be identified as CD56⁺ and PDGFRα⁺ cells, respectively. The purpose of this study was to investigate the osteogenic differentiation potential of human skeletal muscle-derived progenitors. Both CD56⁺ cells and PDGFRα⁺ cells showed comparable osteogenic differentiation potential in vitro. However, in an in vivo ectopic bone formation model, PDGFRα⁺ cells formed bone-like tissue and showed successful engraftment, while CD56⁺ cells did not form bone-like tissue and did not adapt to an osteogenic environment. Immunohistological analysis of human HO sample revealed that many PDGFRα⁺ cells were localized in proximity to ectopic bone formed in skeletal muscle. MicroRNAs (miRNAs) are known to regulate many biological processes including osteogenic differentiation. We investigated the participation of miRNAs in the osteogenic differentiation of PDGFRα⁺ cells by using microarray. We identified miRNAs that had not been known to be involved in osteogenesis but showed dramatic changes during osteogenic differentiation of PDGFRα⁺ cells. Upregulation of miR-146b-5p and -424 and downregulation of miR-7 during osteogenic differentiation of PDGFRα⁺ cells were confirmed by quantitative real-time RT-PCR. Inhibition of upregulated miRNAs, miR-146b-5p and -424, resulted in the suppression of osteocyte maturation, suggesting that these two miRNAs have the positive role in the osteogenesis of PDGFRα⁺ cells. Our results suggest that PDGFRα⁺ cells may be the major source of HO and that the newly identified miRNAs may regulate osteogenic differentiation process of PDGFRα⁺ cells.</p> </div

Changes in miRNA during osteogenic differentiation of PDGFRα⁺ cells.

<p>At the different time points during osteogenic differentiation of PDGFRα⁺ cells, the expressions of miRNAs indicated were quantified by qRT-PCR. Values are represented as the ratio to uninduced cells and shown as means ± s.d. of three independent preparations.</p

Immunohistological analysis of human HO sample.

<p>Human HO sample was subjected to immunofluorescent staining for PDGFRα and subsequently to H-E staining. (A) Image of H-E staining. Scale bar: 100 µm. Right panel shows high magnification image of square region in the left panel. (B) Image of PDGFRα staining. Arrows indicate PDGFRα⁺ cells surrounding ectopic bone tissue. Scale bar: 10 µm.</p