title: Molecular cloning of doublesex genes of four cladocera (water flea) species.
abstract: BACKGROUND
  The gene doublesex (dsx) is known as a key factor regulating genetic sex determination in many organisms. We previously identified two dsx genes (DapmaDsx1 and DapmaDsx2) from a freshwater branchiopod crustacean, Daphnia magna, which are expressed in males but not in females. D. magna produces males by parthenogenesis in response to environmental cues (environmental sex determination) and we showed that DapmaDsx1 expression during embryonic stages is responsible for the male trait development. The D. magna dsx genes are thought to have arisen by a cladoceran-specific duplication; therefore, to investigate evolutionary conservation of sex specific expression of dsx genes and to further assess their functions in the environmental sex determination, we searched for dsx homologs in four closely related cladoceran species.
  
  
  RESULTS
  We identified homologs of both dsx genes from, D. pulex, D. galeata, and Ceriodaphnia dubia, yet only a single dsx gene was found from Moina macrocopa. The deduced amino acid sequences of all 9 dsx homologs contained the DM and oligomerization domains, which are characteristic for all arthropod DSX family members. Molecular phylogenetic analysis suggested that the dsx gene duplication likely occurred prior to the divergence of these cladoceran species, because that of the giant tiger prawn Penaeus monodon is rooted ancestrally to both DSX1 and DSX2 of cladocerans. Therefore, this result also suggested that M. macrocopa lost dsx2 gene secondarily. Furthermore, all dsx genes identified in this study showed male-biased expression levels, yet only half of the putative 5' upstream regulatory elements are preserved in D. magna and D. pulex.
  
  
  CONCLUSIONS
  The all dsx genes of five cladoceran species examined had similar amino acid structure containing highly conserved DM and oligomerization domains, and exhibited sexually dimorphic expression patterns, suggesting that these genes may have similar functions for environmental sex determination in cladocerans.
authors.affiliation: Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, National Institutes of Natural Sciences, and Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Toyota
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Kato
authors.forename: Masaru
authors.initials: M
authors.lastname: Sato
authors.forename: Naomi
authors.initials: N
authors.lastname: Sugiura
authors.forename: Shinichi
authors.initials: S
authors.lastname: Miyagawa
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Miyakawa
authors.forename: Hajime
authors.initials: H
authors.lastname: Watanabe
authors.forename: Shigeto
authors.initials: S
authors.lastname: Oda
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Ogino
authors.forename: Chizue
authors.initials: C
authors.lastname: Hiruta
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizutani
authors.forename: Norihisa
authors.initials: N
authors.lastname: Tatarazako
authors.forename: Susanne
authors.initials: S
authors.lastname: Paland
authors.forename: Craig
authors.initials: C
authors.lastname: Jackson
authors.forename: John K
authors.initials: JK
authors.lastname: Colbourne
authors.forename: Taisen
authors.initials: T
authors.lastname: Iguchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D033361:Cladocera / Q000235:genetics*; D003001:Cloning, Molecular; D017124:Conserved Sequence; D005260:Female; D020440:Gene Duplication; D005786:Gene Expression Regulation; D008297:Male; D058977:Molecular Sequence Annotation; D011401:Promoter Regions, Genetic; D012727:Sex Characteristics; D013045:Species Specificity; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D060829:Arthropod Proteins