“…• Cyanobacteria (Cadoret et al, 2005) • α-proteobacteria (Marden et al, 2011) • γ-proteobacteria (An et al, 2013) • UV-stress adaption (Cadoret et al, 2005) • Cyst formation (Marden et al, 2011) • Biofilm and virulence (An et al, 2013) 3 ,5 -cCMP 3 ,5 -cUMP Using modern mass spectrometry detected in various mammalian cell lines and different organs (Burhenne et al, 2011;Bähre et al, 2015). Additionally also found in zebrafish (Dittmar et al, 2015) and cUMP in a plant (Hartwig et al, 2014) • In general functions are currently mostly unknown (Seifert, 2017) • Both can activate some cAMP/cGMP effectors in vitro (Wolter et al, 2011;Zong et al, 2012) • cCMP potentially involved in processes such as tissue development and cell proliferation, immune responses modulation and platelet aggregation (Bloch et al, 1974;Anderson, 1982;Desch et al, 2010) • Specific cytidylate and uridylate cyclases just recently discovered in species of various phyla (Tal et al, 2021) • Synthesis stimulated by phage infection; activate downstream defense mechanisms (Tal et al, 2021) • Bacterial toxins [e.g., ExoY from P. aeruginosa (Beckert et al, 2014), CyaA from Bordetella pertussis (Göttle et al, 2010), edema factor from Bacillus anthracis (Göttle et al, 2010)] have been demonstrated to be capable of forming cCMP and cUMP 3 ,5 -cIMP Identified in isolated porcine coronary arteries (Chen et al, 2014) • In general functions are currently mostly unknown (Leung et al, 2015) • Involved in hypoxia−induced constriction of porcine coronary arteries (Chen et al, 2014;Nan et al, 2020) • Only very few data available • Detected in Corynebacterium murisepticum (Newton et al, 1998); specificity of the used method is however questioned (Seifert, 2015) 3 ,5 -cTMP 3 ,5 -cXMP Not yet detected in any biological samples using modern and sensitive mass spectrometry techniques…”