title: Methyl farnesoate synthesis is necessary for the environmental sex determination in the water flea Daphnia pulex.
abstract: Sex-determination systems can be divided into two groups: genotypic sex determination (GSD) and environmental sex determination (ESD). ESD is an adaptive life-history strategy that allows control of sex in response to environmental cues in order to optimize fitness. However, the molecular basis of ESD remains largely unknown. The micro crustacean Daphnia pulex exhibits ESD in response to various external stimuli. Although methyl farnesoate (MF: putative juvenile hormone, JH, in daphnids) has been reported to induce male production in daphnids, the role of MF as a sex-determining factor remains elusive due to the lack of a suitable model system for its study. Here, we establish such a system for ESD studies in D. pulex. The WTN6 strain switches from producing females to producing males in response to the shortened day condition, while the MFP strain only produces females, irrespective of day-length. To clarify whether MF has a novel physiological role as a sex-determining factor in D. pulex, we demonstrate that a MF/JH biosynthesis inhibitor suppressed male production in WTN6 strain reared under the male-inducible condition, shortened day-length. Moreover, we show that juvenile hormone acid O-methyltransferase (JHAMT), a critical enzyme of MF/JH biosynthesis, displays MF-generating activity by catalyzing farnesoic acid. Expression of the JHAMT gene increased significantly just before the MF-sensitive period for male production in the WTN6 strain, but not in the MFP strain, when maintained under male-inducible conditions. These results suggest that MF synthesis regulated by JHAMT is necessary for male offspring production in D. pulex. Our findings provide novel insights into the genetic underpinnings of ESD and they begin to shed light on the physiological function of MF as a male-fate determiner in D. pulex.
authors.affiliation: Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Toyota
authors.affiliation: Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Miyakawa
authors.affiliation: Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Department of Biology, Center for Liberal Arts and Sciences, Iwate Medical University, 2-1-1, Nishi-Tokuda, Yahaba-cho, Shiwa-gun, Iwate 028-3694, Japan.
authors.forename: Chizue
authors.initials: C
authors.lastname: Hiruta
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Furuta
authors.affiliation: Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Ogino
authors.affiliation: National Institute of Agrobiological Sciences, 1-2, Oowashi, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shinoda
authors.affiliation: National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
authors.forename: Norihisa
authors.initials: N
authors.lastname: Tatarazako
authors.affiliation: Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Miyagawa
authors.affiliation: School of Public and Environmental Affairs, Indiana University, 1315 East Tenth Street, Bloomington, IN 47405, USA; School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Shaw
authors.affiliation: Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan. Electronic address: taisen@nibb.ac.jp.
authors.forename: Taisen
authors.initials: T
authors.lastname: Iguchi
mesh_terms: D000818:Animals; D060829:Arthropod Proteins / Q000235:genetics / Q000378:metabolism; D003621:Daphnia / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D004777:Environment; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D005260:Female; D007605:Juvenile Hormones / Q000096:biosynthesis; D008297:Male; D012098:Reproduction; D019849:Sex Determination Processes; D012733:Sex Differentiation
chemical_list: D060829:Arthropod Proteins; D005231:Fatty Acids, Unsaturated; D007605:Juvenile Hormones; C032429:methyl farnesoate
keywords: Daphnia pulex; Environmental sex determination; Juvenile hormone acid O-methyltransferase; Methyl farnesoate; Photoperiod