CDNA Cloning Of Aquaporin3in Sarotherodon Melanothern, Oreochromis Niloticus And Tissue Expression Patterns Under Salinity Stresses

Osmoregulation is an important physiological activity in teleosts that regulates theosmotic pressure balance to adapt to varying external environment. Fish in the seawatermaintain osmotic pressure balance by excreting excess salt and absorbing water, incontrast, fish in freshwater maintain osmotic pressure balance by excreting excess waterand absorbing ion. The transportation of water and ion are accomplished by variouschannel proteins and transporters on cell membrane. Aquaporins is one kind of channelproteins and express in the osmoregulatory organs such as gill, kidney and intestine.Aquaporins are very important for teleosts osmoregulation because they can transportnot only water and ion, but also glycerol and urea.In order to understand the role of aquaporin3(AQP3) in osmoregulatory processesof Sarotherodon melanothern and Oreochromis niloticus, cDNA sequences of AQP3was cloned from gill of S. melanothern and O. niloticus by rapid amplification of cDNAends (RACE) and RT-PCR respectively. The same batch of S. melanothern and O.niloticus was acclimated to freshwater,15ppt and30ppt gradually. Five fish was chosenfor sampling randomly one week later. In addition, O. niloticus15ppt and30pptacclimated was transferred to freshwater directly and five fish was chosen for samplingrandomly one week later. Relative tissue expression of AQP3mRNA in differentexperimental group was estimated by real-time quantitative PCR.The results of S. melanothern showed that the full length of AQP3cDNA was1894bp, containing a912bp open reading frame and encoding303amino acids, with a98bp5′untranslated region (UTR) and a884bp3′-UTR. The amino acid sequencecomparison showed that AQP3of S. melanothern shared the highest identity with O. mossambicus (94%). The higher expression were detected in skin, gill and muscle thanother tissues at0and15salinity, moreover, the expression level in15salinity was lowerthan that in freshwater in all tissues. The expression level was higher in intestine than inother tissues at30salinity.The results of O. niloticus showed that the length of sequence was1445bp,containing912bp open reading frame and encoding303amino acids. The amino acidsequence comparison showed that AQP3of O. niloticus shared the highest identity withO. mossambicus (100%). The higher expression was detected in skin, gill, stomach andmuscle than in other tissues in all experiment groups. The expression level of skin, gill,stomach and muscle decreased with the increase of salinity and increased with thedecrease of salinity.In conclusion, the results suggest that AQP3take part in excreting excess water ofgill, skin and muscle during S. melanothern acclimating to freshwater and waterabsorption of intestine during S. melanothern acclimating to seawating, and that AQP3take part in excreting excess water of gill, skin, muscle and stomach during O. niloticusacclimating to freshwater. There may be other AQP but not AQP3take part in waterabsorption of intestine during O. niloticus acclimating to seahwater. This research ishelpful for further understand the osmoregulatory organ and osmoregulation of tilapia.