Ultrasound Monitoring of Thymus Involution in Septic Mice

Thymus involution is characterized by a progressive regression of thymus size and contributes to immunosuppression in sepsis. High-frequency ultrasonography is a non-invasive monitoring system in multiple organs, including the thymus, in mice. However, thymus involution has not been studied using ultrasonography in septic mice. This study reports ultrasound approaches to monitoring septic thymus involution in mice. Sepsis was induced by cecum ligation and puncture (CLP). Mice were euthanized at three time points: baseline and days 3 and 10 after CLP. Thymus areas and volumes were measured using 2-D and 3-D ultrasound approaches. Thymus weights were measured ex vivo. Compared with values at baseline, both thymus area and volume decreased significantly at days 3 and 10. In addition, thymus areas and volumes correlated positively with thymus weights. In conclusion, ultrasonography provides reliable thymus measurements and is an optimal technique for monitoring thymus involution in septic mice.     

Long and branched polyamines are required for maintenance of the ribosome,tRNAHis and tRNATyr in Thermus thermophilus cells at high temperatures

Thermus thermophilus is an extremely thermophilic eubacterium that produces various polyamines. Aminopropylagmatine ureohydrolase (SpeB) and SAM decarboxylase‐like protein 1 (SpeD1) are involved in the biosynthesis of spermidine from arginine. Because long and branched polyamines in T. thermophilus are synthesized from spermidine, the speB and speD1 gene‐deleted strains (ΔspeB and ΔspeD1, respectively) cannot synthesize long and branched polyamines. Although neither strain grew at high temperatures (>75°C) in minimal medium, both strains survived at 80°C when they were cultured at 70°C until the mid‐log phase and then shifted to 80°C. We therefore prepared the ΔspeB and ΔspeD1 cells using this culture method. Microscopic analysis showed that both strains can survive for 10 h after the temperature shift. Although the modification levels of 2′‐O‐methylguanosine at position 18, N⁷‐methylguanosine at position 46, 5‐methyluridine at position 54 and N¹‐methyladenosine at position 58 in the class I tRNA from both strains were normal, amounts of tRNA^Tyr, tRNA^His, rRNAs and 70S ribosomes were decreased after the temperature shift. Furthermore, in vivo protein synthesis in both strains was completely lost 10 h after the temperature shift. Thus, long and branched polyamines are required for at least the maintenance of 70S ribosome and some tRNA species at high temperatures.