title: Differential transcriptomic analyses revealed genes and signaling pathways involved in iono-osmoregulation and cellular remodeling in the gills of euryhaline Mozambique tilapia, Oreochromis mossambicus.
abstract: BACKGROUND
  The Mozambique tilapia Oreochromis mossambicus has the ability to adapt to a broad range of environmental salinities and has long been used for investigating iono-osmoregulation. However, to date most studies have focused mainly on several key molecules or parameters hence yielding a limited perspective of the versatile iono-osmoregulation in the euryhaline fish. This study aimed to capture transcriptome-wide differences between the freshwater- and seawater-acclimated gills of the Mozambique tilapia.
  
  
  RESULTS
  We have identified over 5000 annotated gene transcripts with high homology (E-value <1.0E-50) to human genes that were differentially expressed in freshwater- and seawater-acclimated gills of the Mozambique tilapia. These putative human homologs were found to be significantly associated with over 50 canonical signaling pathways that are operating in at least 23 biological processes in relation to branchial iono-osmoregulation and cellular remodeling. The analysis revealed multiple signaling pathways in freshwater-acclimated gills acting in concert to maintain cellular homeostasis under hypo-osmotic environment while seawater-acclimated gills abounded with molecular signals to cope with the higher cellular turn-over rate, energetics and iono-regulatory demands under hyper-osmostic stress. Additionally, over 100 transcripts encoding putative inorganic ion transporters/channels were identified, of which several are well established in gill iono-regulation while the remainder are lesser known. We have also validated the expression profiles of 47 representative genes in freshwater- and seawater-acclimated gills, as well as in hypersaline-acclimated (two-fold salinity of seawater) gills. The findings confirmed that many of these responsive genes retained their expression profiles in hypersaline-acclimated gills as in seawater-acclimated gills, although several genes had changed significantly in their expression level/direction in hypersaline-acclimated gills.
  
  
  CONCLUSIONS
  This is the first study that has provided an unprecedented transcriptomic-wide perspective of gill iono-osmoregulation since such studies were initiated more than 80 years ago. It has expanded our molecular perspective from a relatively few well-studied molecules to a plethora of gene transcripts and a myriad of canonical signaling pathways driving various biological processes that are operating in gills under hypo-osmotic and hyper-osmotic stresses. These findings would provide insights and resources to fuel future studies on gill iono-osmoregulation and cellular remodeling in response to salinity challenge and acclimation.
authors.affiliation: NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive, 117411 Singapore, Singapore. dbslsh@nus.edu.sg.
authors.forename: Siew Hong
authors.initials: SH
authors.lastname: Lam
authors.forename: Eei Yin
authors.initials: EY
authors.lastname: Lui
authors.forename: Zhengjun
authors.initials: Z
authors.lastname: Li
authors.forename: Shaojiang
authors.initials: S
authors.lastname: Cai
authors.forename: Wing-Kin
authors.initials: WK
authors.lastname: Sung
authors.forename: Sinnakaruppan
authors.initials: S
authors.lastname: Mathavan
authors.forename: Toong Jin
authors.initials: TJ
authors.lastname: Lam
authors.forename: Yuen Kwong
authors.initials: YK
authors.lastname: Ip
mesh_terms: D000818:Animals; D020869:Gene Expression Profiling; D023281:Genomics; D005880:Gills / Q000166:cytology* / Q000378:metabolism*; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D007473:Ion Channels / Q000235:genetics; D058977:Molecular Sequence Annotation; D064587:Osmoregulation / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D054712:Salinity; D015398:Signal Transduction / Q000235:genetics*; D017210:Tilapia / Q000235:genetics* / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D012333:RNA, Messenger