Molecular cloning, expression pattern, and immunocytochemical localization of a gonadotropin-releasing hormone-like molecule in the gastropod mollusk, Aplysia californica

Abstract

Successful reproduction in vertebrates depends upon the actions of gonadotropin-releasing hormone (GnRH). Despite the wide presence of GnRH in Phylum Chordata, GnRH has not been isolated in protostomes other than the common octopus. To provide information on the evolution of this critical hormone, we isolated the full-length cDNA of a GnRH-like molecule from the central nervous system of a gastropod mollusk, the sea hare Aplysia californica. The open reading frame of this cDNA encodes a protein of 147 amino acids. The molecular architecture of the deduced protein is highly homologous to that reported for the prepro-octopus GnRH (oct-GnRH) and consists of a putative signal peptide, a GnRH dodecapeptide, a downstream processing site, and a GnRH-associated peptide (GAP). The deduced amino acid sequence of the Aplysia GnRH (ap-GnRH) is QNYHFSNGWYAG and differs from oct-GnRH by only two amino acids. The transcript for ap-GnRH is widely expressed in the central nervous system (CNS), the ovotestis, and the atrial gland, an exocrine gland. Immunocytochemistry (ICC) using an antiserum against oct-GnRH detected immunoreactive neurons in all CNS ganglia examined, and the staining was abolished by the preadsorption of the antiserum with synthetic ap-GnRH. In sum, ap-GnRH sequence is the first gastropod GnRH-like molecule to be elucidated. Further, it represents one of the only two GnRH-like molecules found outside Phylum Chordata. These data refute the possibility that oct-GnRH arose singly in cephalopods by convergent evolution and provide valuable support for an ancient origin of GnRH during metazoan evolution.

Evolutionary origin of a functional gonadotropin in the pituitary of the most primitive vertebrate, hagfish

“…If this is indeed the case, a key point of interest would be to elucidate the early evolution of the HPG axis, or more simply, the GnRH-GTHgonadal axis. Indeed, GnRHs, including GnRH-like peptides, have been found not only in chordates including amphioxus (26) and tunicates but also in multiple invertebrate phyla (27). Moreover, amphioxus has a complete set of genes for sex steroid hormone-synthesizing enzymes (17), as well as two genes for steroid hormone receptors, one more closely related to vertebrate estrogen receptors (17).…”

Existence and distribution of gonadotropin-releasing hormone-like peptides in the central nervous system and ovary of the Pacific white shrimp, Litopenaeus vannamei

“…Currently, 28 GnRH isoforms have been reported, consisting of 15 isoforms in vertebrates and 13 isoforms in invertebrates Zhang et al 2008;Sower et al 2009;Lindemans et al 2009). All chordate and most invertebrate GnRH isoforms comprise 10 amino acids with an N-terminal pyroglutamyl and C-terminal amidated glycine residue (King and Millar 1995;Tsai 2006).…”

The identification and distribution of gonadotropin-releasing hormone-like peptides in the central nervous system and ovary of the giant freshwater prawn, Macrobrachium rosenbergii

“…The gonadotropins are then released into blood stream and act on the gonads to stimulate gametogenesis and steroidogenesis (Fernald and White 1999). To date, the primary structures of 14 and 11 GnRHs have been identified in vertebrates and invertebrates, respectively (Gorbman and Sower 2003;Tsai 2006;Kah et al 2007;Zhang et al 2007). Among invertebrate GnRHs, nine isoforms identified in the tunicates are decapeptides, whereas two isoforms discovered in the octopus and aplysia are dodecapeptides (Powell et al 1996;Iwakoshi et al 2002;Adams et al 2003;Kavanaugh et al 2005;Zhang et al 2007).…”