| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 103 === The purpose of this thesis is to systemically investigate molecular modulations when euryhaline brackish medaka, Oryzias dancena under cold stress. Fresh water (FW)- and seawater (SW)-acclimated brackish medaka were transferred from 28°C to 18°C. After cold exposure to 18°C for a week, brain, gill and liver were sampled. Next generation sequencing was applied for de novo assembly and transcriptome analyses. The assembled transcripts were further used to KEGG annotation. The numbers of genes in KEGG mapping results were mainly categorized into signal transduction group in all three organs under low temperature. In brain, no specific gene groups or signaling pathways were up-regulated under low temperature comparing with other organs. Expression of some specific genes in pathways belong to environmental information processing were activated in the gill. Up-regulations of gene groups in the liver were mainly found among the pathway of metabolic groups especially in carbohydrate metabolism. Nevertheless, gill is the only organ found with largest numbers of up-regulated gene under low temperature. After cold transfer, the following experiments were performed. In the gill of SW-acclimated brackish medaka, the mRNA abundance of anti-apoptosis factor, baculoviral inhibitor of apoptosis repeat-containing 5 (birc5) and protein level of cleaved-caspase-3 increased. The osmoregulatory protein, Na+, K+-ATPase (NKA) protein and activity declined and ATP-sensitive inward rectifier potassium channel 1 (kcnj1) mRNA abundance increased. On the other hand, decreased mRNA abundance of tight junction and related gene crumbs homolog 3 (crb3) mRNA abundance with increased Na+, K+, 2Cl--cotransporter (NKCC) and kcnj1 were found in the gill of FW-acclimated brackish medaka. In this thesis, large numbers of complete coding sequences and pathways classified of mRNA were found to advantage next experimental usage. To combine pathway speculate and physiological change, different adaptation to 18°C of brackish medaka were found: To compare 18°C and 28°C medaka, kcnj1 mRNA abundant were upregulated at both SW18°C and FW18°C, but apoptosis protein were only upregulated at SW18°C. Coupling with mRNA abundant relating to tight junction were downregulated and NKCC mRNA abundant were upregulated at FW18°C. In conclusion, cell permeability of gill and different reaction of ionocyte to cold stress were critical issues in euryhaline fish.
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