Isotropic susceptibility shift under MAS: the origin of the split water resonances in 1H MAS NMR spectra of cell suspensions

Bulk susceptibility variations in a multiphase system such as cultured cells and tissue have two manifestations: a dipolar field component outside the regular heterogenous region which introduces linebroadening, and an isotropic field part which results in a frequency shift. Previous NMR studies have emphasized the utility of magic angle spinning for averaging the dipolar component, particularly if the spins of interest are limited to one phase of a multiphase system such as a sample of liquid with air pockets or glass beads. However, in analyzing spectra from complex multiphase systems, such as cell suspensions and tissues, etc., the isotropic part is often neglected, leading to questionable interpretation of experimental results. The present study demonstrates that under magic angle spinning, the water resonance in NMR experiments of cell suspensions is split into two resolved peaks due to the isotropic susceptibility shift. These two peaks are assigned to a central core of cell free water and an outer cylindrical ring of tightly packed cells in close association with water. A comprehensive theory for this splitting is provided based on a coaxis cylinder model with different susceptibilities. The frequency difference is shown to be dependent on the susceptibility difference and also on the angle of the rotor in the magnetic field. The splitting distance of the two water peaks can be used to measure the susceptibility difference of water in these two phases. The susceptibility difference was measured for three different cell types: 3T3 F442A preadipocyte cells, mouse embryonic stem cells, and human red blood cells.

Biochemical correlates of thiazolidinedione-induced adipocyte differentiation by high-resolution magic angle spinning NMR spectroscopy

Thiazolidinediones, a class of synthetic ligands to the peroxisome proliferator-activated receptor-gamma, induce terminal adipocyte differentiation of 3T3 F442A cells, and have already been used as alternative therapeutic agents for the treatment of liposarcoma in clinical trials. The biochemical changes occurring in the 3T3 F442A cell line and well-differentiated liposarcoma following induction of adipocyte differentiation with the thiazolidinedione troglitazone were measured using high-resolution magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. 3T3 F442A cell differentiation was characterized by a large accumulation of intracellular triglyceride and withdrawal from the cell cycle. Phosphatidylcholine (PTC), phosphocholine (PC), myo-inositol, and glycerol were found to be possible biochemical markers for adipocyte differentiation induced by thiazolidenediones. The molar ratio of PTC to PC increased fourfold in differentiated 3T3 F442A cells compared to undifferentiated cells, suggesting a substantial increase in CTP:phosphocholine cytidylyltransferase activity with differentiation. A 2.8-fold increase in the PTC:PC ratio was observed in the lipoma-like well-differentiated liposarcoma of three patients who were treated with troglitazone when compared to liposarcoma from patients not treated with this drug. Thus, this ratio may be an NMR-detectable marker of troglitazone efficacy and response to differentiation therapy for liposarcoma.

A recyclable Candida albicans URA3 cassette for PCR product-directed gene disruptions

For some time, gene disruptions in Candida albicans have been made with the hisG-URA3-hisG ('Ura-blaster') cassette, which can be re-used in successive transformations of a single strain after homologous excision of URA3. However, the hisG repeats are too large for efficient PCR amplification of the entire cassette, so it cannot be used for PCR product-directed gene disruptions. We describe here a gene disruption cassette, URA3-dpl200, with 200 bp flanking repeats that permit efficient PCR amplification. After transformation and integration to produce both arg5::URA3-dpl200 and rim101::URA3-dpl200 alleles, we find that arg5::dpl200 and rim101::dpl200 segregants, respectively, can be obtained. We have used the cassette to create rim101::dpl200/rim101::URA3-dpl200 mutants exclusively through PCR product-directed disruption.