title: A transgenerational endocrine signaling pathway in Crustacea.
abstract: BACKGROUND
  Environmental signals to maternal organisms can result in developmental alterations in progeny. One such example is environmental sex determination in Branchiopod crustaceans. We previously demonstrated that the hormone methyl farnesoate could orchestrate environmental sex determination in the early embryo to the male phenotype. Presently, we identify a transcription factor that is activated by methyl farnesoate and explore the extent and significance of this transgenerational signaling pathway.
  
  
  RESULTS
  Several candidate transcription factors were cloned from the water flea Daphnia pulex and evaluated for activation by methyl farnesoate. One of the factors evaluated, the complex of two bHLH-PAS proteins, dappuMet and SRC, activated a reporter gene in response to methyl farnesoate. Several juvenoid compounds were definitively evaluated for their ability to activate this receptor complex (methyl farnesoate receptor, MfR) in vitro and stimulate male sex determination in vivo. Potency to activate the MfR correlated to potency to stimulate male sex determination of offspring (pyriproxyfen>methyl farnesoate>methoprene, kinoprene). Daphnids were exposed to concentrations of pyriproxyfen and physiologic responses determined over multiple generations. Survivial, growth, and sex of maternal organisms were not affected by pyriproxyfen exposure. Sex ratio among offspring (generation 2) were increasingly skewed in favor of males with increasing pyriproxyfen concentration; while, the number of offspring per brood was progressively reduced. Female generation 2 daphnids were reared to reproductive maturity in the absence of pyriproxyfen. Sex ratios of offspring (generation 3) were not affected in this pyriproxyfen lineage, however, the number of offspring per brood, again, was significantly reduced.
  
  
  CONCLUSIONS
  Results reveal likely components to a hormone/receptor signaling pathway in a crustacean that orchestrates transgenerational modifications to important population metrics (sex ratios, fecundity of females). A model is provided that describes how these signaling processes can facilitate population sustainability under normal conditions or threaten sustainability when perturbed by environmental chemicals.
authors.affiliation: Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, North Carolina, United States of America. Gerald_leblanc@ncsu.edu
authors.forename: Gerald A
authors.initials: GA
authors.lastname: LeBlanc
authors.forename: Ying H
authors.initials: YH
authors.lastname: Wang
authors.forename: Charisse N
authors.initials: CN
authors.lastname: Holmes
authors.forename: Gwijun
authors.initials: G
authors.lastname: Kwon
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Medlock
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D003445:Crustacea / Q000187:drug effects / Q000378:metabolism*; D003621:Daphnia / Q000187:drug effects / Q000502:physiology; D004703:Endocrine System / Q000187:drug effects / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005260:Female; D005298:Fertility; D017930:Genes, Reporter; D008018:Life Cycle Stages / Q000187:drug effects; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D011156:Population Density; D011725:Pyridines / Q000494:pharmacology; D019849:Sex Determination Processes / Q000187:drug effects; D012744:Sex Ratio; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000737:chemistry
chemical_list: D005231:Fatty Acids, Unsaturated; D008024:Ligands; D011725:Pyridines; D014157:Transcription Factors; C032429:methyl farnesoate; C055613:pyriproxyfen; D008156:Luciferases