Bag cell peptide acts directly on ovotestis of Aplysia californica: Basis for an in vitro bioassay

Abstract

Extracts of the parietovisceral ganglion (PVG) of Aplysia californica cause release of eggs from isolated fragments of ovotestis. Spontaneous release of eggs by ovotestis in vitro is similar in artificial sea water (ASW) and hemolymph; PVG extracts increase egg release in ASW and hemolymph similarly. PVG-induced egg release is dose dependent in vitro. The number of eggs released in vitro by PVG extract or by ASW alone increases with time after oviposition. Extracts of genital or pleural ganglia or of branchial nerve do not increase egg release above control levels in ASW; isolated bag cell clusters are most effective at inducing egg release. PVG-induced egg release persists after the extract is boiled but not after incubation with trypsin or protease. These in vitro results are consistent with previous in vivo studies on egg-laying and provide evidence that a bag cell peptide acts directly on the ovotestis. Therefore, egg release in vitro appears to be a function of peptide concentration and oviposition history. The logarithmic relation between PVG concentration and relative egg release provides an in vitro bioassay for the bag cell peptide(s).