Isolation of an egg-laying hormone-binding protein from the gonad of Aplysia californica and its localization in oocytes

Abstract

A protein solubilized from a membrane preparation of the gonad of Aplysia californica has been isolated by affinity chromatography, using bag cell egg-laying hormone (ELH) as the bound ligand, and partially purified and characterized by gel electrophoresis. The protein has an apparent molecular weight of 52 kDa and consists of two disulfide-linked subunits of about 30 kDa each. The protein is glycosylated and has an acidic pI. Approximately 10-15 micrograms of this protein can be isolated from a single ovotestis, representing less than 1% of the total protein in the gonad; but the protein could not be detected in buccal mass or body wall, tissues which do not have apparent response to ELH. Antibodies generated against this ELH-binding protein (ELHBP) were used to localize sites in the ovotestis which might contain this molecule and thus represent targets for egg-laying hormone. Immunocytochemical results indicate that the oocytes are a rich source of this protein, since their cytoplasm was the only detectable site of immunoreactivity. Whether this binding protein represents an egg-laying hormone receptor is uncertain, but its prevalence in oocytes suggests that ELH plays a signaling role on these gametes.

Egg-laying-hormone immunoreactivity in the neural ganglia and ovary of Haliotis asinina Linnaeus

“…5e). In higher gastropods (Lymnaea and Aplysia) the ELHs were also detected in the female reproductive tract (the oothecal gland, muciparous gland, pars contorta, and ovotestis, respectively) but none have been reported in the ovarian tissue (Choate et al 1993;Van Minnen et al 1989). It was suggested that ELH expressed in the reproductive tissues of these higher gastropods might belong to a different isotype from that expressed in the neural tissues (Fisher et al 1988).…”

The neuroendocrine bag cells of Aplysia: a model system for neural control of hormone secretion

“…The afterdischarge then triggers the secretion of a number of bag-cell peptides, including ELH, into the hemolymph (Kupfermann 1970, Chiù et al 1979, Newcomb & Scheller 1990, Wayne 1994. ELH then diffuses to the ovotestis where it triggers ovulation (Coggeshall 1970, Choate et al 1993. Whether there are steroid secretions from the ovotestis that feedback on either the cerebral ganglion or bag cells to regulate ELH secretion has not been determined.…”

Nitric oxide induces aspects of egg-laying behavior in Aplysia

“…It has been suggested that the sequencing of egg laying, and its interactions with other behaviors, arises through the actions of a number of neuroendocrine bag cell peptides (Scheller et al, 1983;Scheller and Axel, 1984). Support for this hypothesis comes from the finding that different bag cell peptides directly affect a variety of neural targets (Branton et al, 1978;Sigvardt et al, 1986;, as well as directly affecting the gonad and causing the release of eggs (Choate et al, 1993;Coggeshall, 1970;Rothman et al, 1983b). However, other experiments also showed that aspects of egg-laying behavior are initiated or regulated neurally, as feed-forward or feedback responses to stimuli originating in other portions of the sequence (Cobbs and Pinsker, 1982b;Ter Maat and Ferguson, 1996).…”

“…The direct effects of a variety of bag cell peptides on a number of tissues has been shown, supporting this idea. For example, ELH directly affects the gonads and causes egg release (Choate et al, 1993;Coggeshall, 1970;Rothman et al, 1983b), and directly affects central neurons in the buccal and cerebral ganglia and thereby inhibits feeding (Ram, 1982;Ram, 1983;Teyke et al, 1991), whereas additional peptides cause depolarization of the bag cells as part of a positive feedback loop Kauer et al, 1987;Rothman et al, 1983a). It has also been suggested that egg laying is coordinated by feed-forward and feedback loops (Cobbs and Pinsker, 1982b;Ferguson et al, 1989b;Ter Maat and Ferguson, 1996).…”