title: Localization and functional characterization of a novel adipokinetic hormone in the mollusk, Aplysia californica.
abstract: Increasing evidence suggests that gonadotropin-releasing hormone (GnRH), corazonin, adipokinetic hormone (AKH), and red pigment-concentrating hormone all share common ancestry to form a GnRH superfamily. Despite the wide presence of these peptides in protostomes, their biological effects remain poorly characterized in many taxa. This study had three goals. First, we cloned the full-length sequence of a novel AKH, termed Aplysia-AKH, and examined its distribution in an opisthobranch mollusk, Aplysia californica. Second, we investigated in vivo biological effects of Aplysia-AKH. Lastly, we compared the effects of Aplysia-AKH to a related A. californica peptide, Aplysia-GnRH. Results suggest that Aplysia-AKH mRNA and peptide are localized exclusively in central tissues, with abdominal, cerebral, and pleural ganglia being the primary sites of Aplysia-AKH production. However, Aplysia-AKH-positive fibers were found in all central ganglia, suggesting diverse neuromodulatory roles. Injections of A. californica with Aplysia-AKH significantly inhibited feeding, reduced body mass, increased excretion of feces, and reduced gonadal mass and oocyte diameter. The in vivo effects of Aplysia-AKH differed substantially from Aplysia-GnRH. Overall, the distribution and biological effects of Aplysia-AKH suggest it has diverged functionally from Aplysia-GnRH over the course of evolution. Further, that both Aplysia-AKH and Aplysia-GnRH failed to activate reproduction suggest the critical role of GnRH as a reproductive activator may be a phenomenon unique to vertebrates.
authors.affiliation: Department of Integrative Physiology and Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Joshua I
authors.initials: JI
authors.lastname: Johnson
authors.affiliation: Department of Integrative Physiology and Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Scott I
authors.initials: SI
authors.lastname: Kavanaugh
authors.affiliation: Department of Integrative Physiology and Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Cindy
authors.initials: C
authors.lastname: Nguyen
authors.affiliation: Department of Integrative Physiology and Center for Neuroscience, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Pei-San
authors.initials: PS
authors.lastname: Tsai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001048:Aplysia / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001835:Body Weight / Q000187:drug effects*; D019143:Evolution, Molecular; D005247:Feeding Behavior / Q000187:drug effects*; D017952:Ganglia, Invertebrate / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism
chemical_list: D009842:Oligopeptides; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; C022059:red pigment-concentrating hormone; D011761:Pyrrolidonecarboxylic Acid