We observed in vitro that after treatment with the Arg-Gly-Asp (RGD) peptide, non-spreading Crassostrea gigas hemocytes underwent cell death. Utilizing a combination of a Hoechst staining method and a DNA fragmentation assay, the typical features of apoptosis were shown, i.e. cell shrinkage, membrane blebbing, chromatin condensation, and DNA fragmentation. The hemocyte cell death caused by the RGD peptide appears to be sequence-specific, since no induction was shown in the alanine-substituted control peptide (RAD) treatment. Interestingly, the glutamic acid-substituted control peptide (RGE) also induced hemocytic cell death, but a different type of the death to that induced by the RGD peptide. This is the first report that specific peptides induce cell death in molluscan hemocytes.
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