title: Transcriptome analysis reveals the molecular mechanisms underlying growth superiority in a novel grouper hybrid (Epinephelus fuscogutatus♀ × E. lanceolatus♂).
abstract: BACKGROUND
  Groupers (Epinephelus spp.) have been widely cultivated in China and South-East Asian countries. As a novel hybrid offspring crossed between E. fuscogutatus♀ and E. lanceolatus♂, Hulong grouper exhibits significant growth superiority over its female parent, which made it a promising farmed species in grouper aquaculture industry in China. Hulong grouper present a good combination of beneficial traits from both parent species, but the molecular mechanisms of its heterosis still remain poorly understood.
  
  
  RESULTS
  Based on RNA sequencing and gene expression profiling, we conducted comparative transcriptome analyses between Hulong grouper and its parents E. fuscoguttatus & E. lanceolatus. Six hundred sixty-two and 5239 differentially expressed genes (DEGs) were identified in the brains and livers, respectively. GO enrichment analysis of these DEGs revealed that metabolic process and catalytic activity were the most enriched GO terms. Further analysis showed the expressions of GnRH1 and GnRH3 in the brain, and GH/IGF axis related genes such as IGF-1, IGF-2b, IGFBP-1, IGFBP-2, IGFBP-4 and IGFBP-5a in the liver of the hybrid F1 were significantly up-regulated, which is in accordance with the growth superiority of hybrid grouper. Meanwhile, expressions of genes related to the protein and glycogen synthesis pathway, such as PI3KC, PI3KR, Raptor, EIF4E3, and PP1 were up-regulated, while PYG expression was down-regulated. These changes might contribute to increased protein and glycogen synthesis in the hybrid grouper.
  
  
  CONCLUSIONS
  We identified a number of differentially expressed genes such as GnRH1 and GnRH3, and genes involved in GH/IGF axis and its downstream signaling pathways for protein and glycogen synthesis in Hulong Grouper. These findings provided molecular basis underlying growth superiority of hybrid grouper, and comprehensive insights into better understanding the molecular mechanisms and regulative pathways regulating heterosis in fish.
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. yingsun09@163.com.|Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. yingsun09@163.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. cyguo@163.com.
authors.forename: Chuan-Yu
authors.initials: CY
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. wangdengdong@hotmail.com.
authors.forename: Deng-Dong
authors.initials: DD
authors.lastname: Wang
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. bgistone@163.com.
authors.forename: Xiao Feng
authors.initials: XF
authors.lastname: Li
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. xiaoling459@126.com.
authors.forename: Ling
authors.initials: L
authors.lastname: Xiao
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. zhangxinhui@genomics.cn.|Guangdong Provincial Key Lab of Molecular Breeding in Marine Economic Animals, Shenzhen, 518083, China. zhangxinhui@genomics.cn.
authors.forename: Xinhui
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. youxinxin@genomics.cn.|Guangdong Provincial Key Lab of Molecular Breeding in Marine Economic Animals, Shenzhen, 518083, China. youxinxin@genomics.cn.
authors.forename: Xinxin
authors.initials: X
authors.lastname: You
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. shiqiong@genomics.cn.|Guangdong Provincial Key Lab of Molecular Breeding in Marine Economic Animals, Shenzhen, 518083, China. shiqiong@genomics.cn.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Shi
authors.affiliation: Shenzhen Key Lab of Marine Genomics, BGI, Shenzhen, 518083, China. 915301589@qq.com.|Guangdong Provincial Key Lab of Molecular Breeding in Marine Economic Animals, Shenzhen, 518083, China. 915301589@qq.com.
authors.forename: Guo-Jun
authors.initials: GJ
authors.lastname: Hu
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. fangchao@genomics.cn.
authors.forename: Chao
authors.initials: C
authors.lastname: Fang
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. lsslhr@mail.sysu.edu.cn.
authors.forename: Hao-Ran
authors.initials: HR
authors.lastname: Lin
authors.affiliation: State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China. lsszy@mail.sysu.edu.cn.|Guangdong Provincial Key Lab of Molecular Breeding in Marine Economic Animals, Shenzhen, 518083, China. lsszy@mail.sysu.edu.cn.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000818:Animals; D001492:Bass / Q000235:genetics* / Q000254:growth & development*; D001921:Brain / Q000502:physiology; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D063990:Gene Ontology; D016678:Genome; D006823:Hybrid Vigor; D008099:Liver / Q000502:physiology; D008297:Male; D060888:Real-Time Polymerase Chain Reaction