In mammals, two classes of cGMPforming enzymes have been identified: the soluble, nitric oxide -dependent guanylyl cyclase and the particulate guanylyl cyclases that are activated by natriuretic peptides. cGMP has an impact on various physiological processes such as smooth muscle relaxation, platelet aggregation and phototransduction. Not surprisingly, the cGMP signaling cascade has become an important pharmacological target, with successful regimens developed for the therapy of heart failure, arterial hypertension and erectile dysfunction. C. elegans was first established as laboratory model organism by Sydney Brenner in 1974. It has become a favored model organism in genetic studies due, in part, to the completion of its genome sequence in 1998. Forty-two percent of the approximately 20,000 predicted C. elegans genes have homology to human genes, including those encoding guanylyl cyclases. Until now, it has not been shown biochemically that the daf-11 loss of function mutant indeed contains less cGMP than wild-type animals. Moreover, C. elegans studies using phosphodiesterase lossof-function mutants in phototransduction experiments or adenylyl cyclase-overexpressing mutants in axon regeneration experiments also assumed higher levels of cNMPs. While it may seem logical to assume that removal of one of the thirty-two guanylyl cyclase enzymes from C. elegans might result in lower intracellular levels of cGMP, studies from mammalian cardiac tissue highlight the complexity of cNMP metabolism. The intracellular concentrations of a given cNMP is a reflection of the balance between its synthesis its degradation, coordinated cross-talk between the cAMP and cGMP metabolic pathways, and of allosteric regulation of enzyme function. From the studies in mammalian cells, we can anticipate that the six different cAMP and cGMP phosphodiesterases in C. elegans are likely to be allosterically regulated by cGMP and cAMP, respectively, and subject to competitive inhibition as well. Thus, removal of the catalytic enzyme may produce unanticipated outcomes in cNMP concentrations. For example, it is feasible that a reduced level of cGMP synthesis might lead to an increase in intracellular cAMP, due to lack of allosteric inhibition by the corresponding phosphodiesterase. In such a situation, cAMP might unexpectedly be the effector molecule mediating biological functions. The relatively simpler C. elegans genetics system affords particular advantages for the analysis of such a complicated array of regulatory connections. However, even though C. elegans has fewer tissues and fewer gene splice Tulathromycin B variants than mammalian systems, there are inherent complexities in an organism with thirty-two guanylyl cyclases, four adenylyl cyclases, and six phosphodiesterase genes that are incompletely characterized biochemically. In the present study, we established a highly specific HPLC-coupled tandem mass-spectrometry method for the simultaneous detection and quantitation of cAMP and cGMP in C. elegans. We used the Folinic acid calcium salt pentahydrate nematode 
as a model organism to examine the influence of reactive oxygen species on cNMP metabolism and lifespan. The assays were directed towards a better understanding of the roles of the guanylyl cyclase daf-11, cGMP phosphodiesterase, and cGMP-dependent protein kinase within the oxidative stress response of the nematode. Tumor heterogeneity can be characterized by differential expression of cell surface markers, genetic and epigenetic differences, and/or differences in key signaling molecules or effectors of cell function. Cellular heterogeneity can be characterized by differences in the functional properties of cells. Whereas many investigations have opted to associate cell surface markers in tumor cells found at the primary tumor site with CSC-behavioral properties.