This investigation has resulted in the chemical identificationand isolation of the egg-laying hormone from Aplysia californica,Aplysia vaccaria, and Aplysia dactylomela. The hormone, which wasoriginally identified as the Bag Cell-Specific protein (BCS protein)on polyacrylamide gels, is a polypeptide of molecular weight ≈ 6000,which is localized in the neurosecretory bag cells of the parietovisceralganglion and the surrounding connective tissue sheath whichcontains the bag cell axons. All three species produce a hormone ofsimilar molecular weight, but varying electrophoretic mobility as determinedon polyacrylamide gels. As tested, the hormone is completelycross-reactive among the three species.
Although the bag cells of sexually immature animals contain theactive hormone, sexual maturation of the animal results in a 10-foldincrease in the BCS protein content of these neurons.
A seasonal variation in the BCS protein content was also observed,with 150 times more hormone contained in the bag cells ofAplysia californica in August than in January. This correlates wellwith the variation in the animals' ability to lay eggs throughout theyear (Strumwasser et al., 1969). There are some indications that thereceptivity of the animal to the available hormone also fluctuatesduring the year, being lower in winter than in swmner. The seasonalrhythm of the other species, Aplysia vaccaria and Aplysia dactylomela,has not been investigated.
A polyacrylamide gel electrophoresis analysis of water-solubleproteins in Aplysia californica revealed several other nerve-specificproteins. One of these is also located in the bag cell somas and stainsturquoise with Amido Schwarz. The function of this protein has not beeninvestigated.
