Differential accumulation of transcripts encoding sulfur assimilation enzymes upon sulfur and/or nitrogen deprivation in Arabidopsis thaliana.

Expression of nine genes encoding enzymes involved in the sulfur assimilation pathway was examined by RNA blot hybridization. Significantly increased levels of transcripts encoding ATP sulfurylase and APS reductase were apparent under sulfur deprivation. However, in the absence of nitrogen, their responsiveness to sulfur deprivation was markedly reduced. Results suggest that the sulfur assimilation pathway is regulated at the transcriptional level by both nitrogen and sulfur sources.

In vivo and in vitro invasiveness of human lung carcinoma cell lines.

Eight cell lines derived from human non-small cell lung carcinomas were used to compare their in vivo invasiveness, in vitro chemoinvasive abilities and type IV collagenase activity. For the evaluation of the in vivo invasive potential, the tumor cells were seeded into deepithelialized rat tracheas and transplanted subcutaneously into nude mice. The invasive behavior of the cells was observed at 4, 8 and 12 weeks and assessed histologically by determination of the levels of penetration of tumor cells into the different layers of the tracheal wall. Except for two cell lines that did not grow at all in vivo, there was a very good correspondence between the levels of in vivo tracheal wall penetration and the in vitro chemoinvasion assay using fibronectin as chemoattractant and Matrigel as barrier. This also correlated very well with the capacity of the cells to secrete type IV collagenase. The in vivo evaluation of invasion using tracheal transplants, although requiring several weeks of experimentation, proved to be very reliable, yielding homogeneous results with little internal variation, and is proposed as a dependable in vivo invasion assay that closely mimics the in vivo human conditions in which most carcinomas develop and eventually invade neighboring tissues.