No abstract

Heat stress (HS) stimulates mitochondrial reactive oxygen species (ROS) production and protein degradation in skeletal muscle. The present study investigated the stimulatory effects of HS-induced mitochondrial ROS production on the ubiquitin-proteasome protein degradation system in primary cultured avian muscle cells. Cells were isolated from the breast muscle of neonatal chicks, and then grown for 48 h. Thereafter, the cells were subjected to 37℃ or 41℃ (HS). Exposure to 6 h of HS treatment significantly decreased the cellular protein content compared to that of normal cells, an effect was completely suppressed by the addition of a proteasome-specific inhibitor. Whereas the mRNA levels of the 20S proteasome C2 subunit, which is one of the subunits of the 26S proteasome, did not change at any time during HS treatment (1, 3, 6 h), the mRNA levels of atrogin-1 and muscle ring-finger protein 1, both of which are muscle-specific ubiquitin ligases, increased after 1 h of HS but then decreased to near-normal values with time. Intracellular ROS production (the sum of H 2 O 2 , hydroxyl radicals, peroxyl radicals, peroxynitrite) did not change in the 1 h HS-exposed cells, but was significantly increased after 3 h and 6 h of HS. Mitochondrial superoxide production was significantly increased after 1 h of HS, which might increase the mRNA expression of ubiquitin ligase in muscle cells. In cells pretreated with 4-hydroxy TEMPO, which is able to decrease mitochondrial superoxide production, the increases in mitochondrial superoxide production and ubiquitin ligase mRNA levels observed after 1 h of HS were suppressed. The protein content of these cells was not decreased, which was observed after the longest period of HS (6 h). These findings suggest that mitochondrial superoxide production may play an important role in activating the ubiquitin-proteasome system, probably via the induction of ubiquitin ligases, in HS-exposed muscle cells.

Plasmid-like DNA (plDNA) was found in 10 out of 61 field isolates of Fusarium oxysporum. These 10 isolates were distributed among 6 formae speciales. Electron microscopic analysis revealed that all these plDNAs were linear molecules. The sizes of plDNAs found were varied from 1.9 to 8.0kb. The sequence homology among four 1.9kb plDNAs, pFOA, pFOL, pFOC and pFOR found in four different F. oxysporum formae speciales was examined by Southern blot analysis, using nick-translated plDNAs as probes. Considerable sequence homology was observed among pFOA, pFOL and pFOC DNA, but pFOR had no homology with three other 1.9kb plasmid DNAs. pFOM and pFOB DNAs of the sizes of 8.0 and 2.2kb, respectively, had no sequence homology with four plDNAs of 1.9kb.

No abstract

No abstract