A marine diatom-derived aldehyde induces apoptosis in copepod and sea urchin embryos

The diatom-derived aldehyde 2-trans-4-trans-decadienal (DD) was tested as an apoptogenic inducer in both copepod and sea urchin embryos, using terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labelling (TUNEL), DNA fragmentation profiling (laddering) and an assay for caspase-3 activity. DD induced TUNEL positivity and DNA laddering, but not caspase-like activation, in copepod embryos spawned by females fed for 10-15 days the diatom diet Thalassiosira rotula Meunier (in vivo), or when newly spawned eggs were exposed for 1 h to 5 mug ml(-1) DD (in vitro). To our knowledge, this is the first time that evidence for an apoptotic process in copepods has been obtained by cytochemical (TUNEL) and biochemical (DNA fragmentation) approaches. The absence of caspase-like activity in copepod embryos suggests that caspase-independent programmed cell death occurs in these organisms. In sea urchin embryos, DD induced apoptosis and also activated a caspase-3-like protease. The saturated aldehyde decanal induced apoptosis at higher concentrations and after a longer incubation period than DD, indicating that alpha,beta-unsaturation of the molecule, coupled with the aldehyde group, is responsible for the greater biological activity of DD. Since diatoms are an important food source for marine herbivores such as copepods and sea urchins, these findings may help explain why unsaturated aldehydes; often induce reproductive failure, with important ecological consequences at the population level.