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The functional maturation process of medullary-type CD4(-)CD8(+) [CD8 single-positive (SP)] thymocytes remains largely uncharacterized. We describe a phenotypic analysis of CD8 SP medullary-type thymocytes and find a remarkable heterogeneity within this thymic cell population. While mature CD8(+) T cells in the periphery are relatively homogeneous (TCRalphabeta(+)CD3(+)Qa-2(+) HSA(-)3G11(-)6C10(-)CD69(-)), CD8 SP medullary-type thymocytes contain discrete subpopulations that can be identified by differential expression of several cell-surface markers. We have identified at least six discrete subpopulations in the subset of TCRalphabeta(+)CD3(+) CD8 SP cells in the thymus. According to the expressed phenotypes, a linear developmental pathway is predicted among these CD8 SP subpopulations as follows: 6C10(+)CD69(+)HSA(hi)3G11(+)Qa-2(-) --> 6C10(-)CD69(+)HSA(hi/int)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(int)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(lo)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(-/lo)3G11(-)Qa-2(-) --> 6C10(-)CD69(-)HSA(-/lo)3G11(-)Qa-2(+). This study provides a framework for understanding CD8 SP T cell maturation in the thymic medulla.

The recombination efficiency and cell specificity of Cre driver lines are critical for exploring pancreatic β cell biology with the Cre/LoxP approach. Some commonly used Cre lines are based on the short Ins2 promoter fragment and show recombination activity in hypothalamic neurons; however, whether this stems from endogenous Ins2 promoter activity remains controversial. In this study, we generated Ins2-Cre knockin mice with a targeted insertion of IRES-Cre at the Ins2 locus and demonstrated with a cell lineage tracing study that the Ins2 gene is not transcriptionally active in the hypothalamus. The Ins2-Cre driver line displayed robust Cre expression and activity in pancreatic β cells without significant alterations in insulin expression. In the brain, Cre activity was mainly restricted to the choroid plexus, without significant recombination detected in the hippocampus or hypothalamus by the LacZ or fluorescent tdTomato reporters. Furthermore, Ins2-Cre mice exhibited normal glucose tolerance and insulin secretion upon glucose stimulation in vivo. In conclusion, this Ins2-Cre driver line allowed high-fidelity detection of endogenous Ins2 promoter activity in vivo, and the negative activity in the hypothalamus demonstrated that this system is a promising alternative tool for studying β cell biology.

Phosphate-solubilizing bacteria (PSB) increase phosphate bioavailability, thereby reducing the application frequency of chemical fertilizers in the production of Nicotiana tabacum (tobacco). In this study, PSB were isolated from tobacco plants for the fi rst time. These PSB were screened in vitro for their ability to solubilize inorganic P (Pi) when grown in association with tobacco plants. Thirty-six PSB with the ability to solubilize P i were isolated and screened for their indolyl-3-acetic acid and siderophore-producing capabilities. In addition, all 36 PSB strains had a partial fragment of their 16S rRNA gene sequenced. The analysis revealed high sequence identity to 16S rDNA sequences from Bacillus, Arthrobacter, Providencia, Enterobacter, Proteus, Psychrobacter, Serratia, Rhodococcus, Pseudomonas, Ochrobactrum, and Acinetobacter. Of the 36 PSB strains analyzed, three (Psychrobacter alimentarius HB15, Enterobacter ludwigii HB21, and Ochrobactrum haematophilum HB36) were selected for a controlled plant inoculation experiment. Inoculation of tobacco plants with these bacterial strains signifi cantly increased plant dry weight. Additionally, inoculation increased P, K, and N uptake by tobacco seedlings as well as soil P availability. The increases observed with inoculation were even more pronounced when tricalcium phosphate (TCP) was added to the soil. The phosphate-solubilizing activity of these three strains was correlated with the release of gluconic, tartaric, acetic, and citric organic acids. Overall, co-inoculation of PSB and TCP appears to represent a promising option for increasing the yield of tobacco plants. The adoption of this technique could provide a pathway to reducing fertilizer input in agricultural settings.

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