Developmental stage-specific expression and tissue distribution of pierisin-1, a guanine-specific ADP-ribosylating toxin, in Pieris rapae

Abstract

The cabbage butterfly (Pieris rapae) produces pierisin-1, an apoptosis-inducing protein against mammalian cells. In order to clarify the biological role of pierisin-1 in P. rapae, its expression during developmental stages was examined. Low levels of pierisin-1 mRNA and protein were detected in first-instar larvae. During growth until the fifth-instar larval stage, the amounts of the mRNA steadily increased to reach about 50-100 times the initial level. Then it rapidly decreased before pupation. The levels of mRNA in the pupae and the adults were as low as in the first-instar larvae. Levels of pierisin-1 protein also increased around 100 times from the first-instar to the fifth-instar larvae and then gradually decreased by over 90% during the pupal stage. Immunostaining of pierisin-1 demonstrated the protein to be mainly located in fat bodies of fifth-instar larvae and early-phase pupae. Although the staining intensity was low, fat bodies of early instars of the larvae and adults were also found to be positive. Moreover, examination of isolated fat body and other tissue samples of the insects were consistent with the above observations. Thus, the results indicate that mRNA of pierisin-1 was highly expressed in late stages of larvae, and that the protein accumulated in fat bodies where it persists during pupation.