title: Gene expression analysis at the onset of sex differentiation in turbot (Scophthalmus maximus).
abstract: BACKGROUND
  Controlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, hence the importance of knowing how the sexual phenotype is established in fish. Turbot, a very important fish for the aquaculture industry in Europe, shows one of the largest sexual growth dimorphisms amongst marine cultured species, being all-female stocks a desirable goal for the industry. Although important knowledge has been achieved on the genetic basis of sex determination (SD) in this species, the master SD gene remains unknown and precise information on gene expression at the critical stage of sex differentiation is lacking. In the present work, we examined the expression profiles of 29 relevant genes related to sex differentiation, from 60 up to 135 days post fertilization (dpf), when gonads are differentiating. We also considered the influence of three temperature regimes on sex differentiation.
  
  
  RESULTS
  The first sex-related differences in molecular markers could be observed at 90 days post fertilization (dpf) and so we have called that time the onset of sex differentiation. Three genes were the first to show differential expression between males and females and also allowed us to sex turbot accurately at the onset of sex differentiation (90 dpf): cyp19a1a, amh and vasa. The expression of genes related to primordial germ cells (vasa, gsdf, tdrd1) started to increase between 75-90 dpf and vasa and tdrd1 later presented higher expression in females (90-105 dpf). Two genes placed on the SD region of turbot (sox2, fxr1) did not show any expression pattern suggestive of a sex determining function. We also detected changes in the expression levels of several genes (ctnnb1, cyp11a, dmrt2 or sox6) depending on culture temperature.
  
  
  CONCLUSIONS
  Our results enabled us to identify the first sex-associated genetic cues (cyp19a1a, vasa and amh) at the initial stages of gonad development in turbot (90 dpf) and to accurately sex turbot at this age, establishing the correspondence between gene expression profiles and histological sex. Furthermore, we profiled several genes involved in sex differentiation and found specific temperature effects on their expression.
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain. diego.robledo@usc.es.
authors.forename: Diego
authors.initials: D
authors.lastname: Robledo
authors.affiliation: Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), 08003, Barcelona, Spain. lribas@icm.csic.es.
authors.forename: Laia
authors.initials: L
authors.lastname: Ribas
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, 36390, Vigo, Spain. rosa.cal@vi.ieo.es.
authors.forename: Rosa
authors.initials: R
authors.lastname: Cal
authors.affiliation: Departamento de Genética. Facultad de Veterinaria, Universidade de Santiago de Compostela, Campus de Lugo, 27002, Lugo, Spain. lauraelena.sanchez@usc.es.
authors.forename: Laura
authors.initials: L
authors.lastname: Sánchez
authors.affiliation: Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), 08003, Barcelona, Spain. piferrer@icm.csic.es.
authors.forename: Francesc
authors.initials: F
authors.lastname: Piferrer
authors.affiliation: Departamento de Genética. Facultad de Veterinaria, Universidade de Santiago de Compostela, Campus de Lugo, 27002, Lugo, Spain. paulino.martinez@usc.es.
authors.forename: Paulino
authors.initials: P
authors.lastname: Martínez
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain. anamaria.vinas@usc.es.
authors.forename: Ana
authors.initials: A
authors.lastname: Viñas
mesh_terms: D000818:Animals; D005260:Female; D005306:Fertilization; D005412:Flatfishes / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D020869:Gene Expression Profiling; D053263:Gene Regulatory Networks; D008297:Male; D040641:Quantitative Trait Loci / Q000235:genetics; D012733:Sex Differentiation / Q000235:genetics*; D013696:Temperature