ABSTRACT: Recent evidences have demonstrated phosphatidylinositol3-kinase (PI3-K)/Akt signaling pathway participates in cell growth, cell survival, and adipocyte differentiation in vitro. However, the in vivo evidence to support Akt function on adipogenesis is limited. To achieve this goal, we generated the stable zebrafish transgenics of Tg(krt4:myrAkt1)cy18 carrying human constitutive active form of Akt1 (myrAkt1) that driven by a skin-specific krt4 promoter. The Tg(krt4:myrAkt1)cy18 display severely skin hypertrophy at embryonic stages, and support Akt1 function as a key gene on cell size control. When transgenics reached sexual maturation, they display obese phenotype due to adipocyte hypertrophy and up-regulation of adipogenesis-related genes. Collectively, our findings provided a direct evidence to support Akt play provital roles on cell size control as well as adipogenesis in vivo. In addition, the obese zebrafish line of Tg(krt4:myrAkt1)cy18 provide a new platform to study obesity and its related chronic diseases mechanism in vivo. The AB strain of Zebrafish (Danio rerio) were obtained from ZIRC (http://zebrafish.org/zirc/home/guide.php), and kept in the stock of Chung Yuan Christian University. Zebrafish were raised in a local tap water at 28.0±0.5℃ and under a constant photoperiodism of 14 hour light cycle/10 hour dark cycle. Zebrafish embryos were collected in 10 cm diameter Petri dishes containing 20 mL fish water after spawning and raised at 28.0±0.5℃. To prevent the disease of Zebrafish embryo, few drops methylen blue were added into fish water. At 5 to 7 dpf, larvae were transferred to 10 liter tanks containing 8.0 liter of fish water and fed with living Paramecium. After 14 dpf, larvae were feed with living artemia (OSI, USA) until adulthood. We dissected two tail tissues (as a pooled sample) from six month-old wild-type and Tg(krt4:myrAkt1)cy18 (n=5), and homogenized in Trizol reagent (Ambion) to isolate total RNA according to the manufacture instruction. The RNA was treated with DNase I at 25℃ for 10 minutes to remove DNA contamination and then cleanup by RNase-free spin columns (Qiagen). The total RNA concentration was determined by spectrophotometry (ND-1000 ; NanoDrop Technol, Wilmington, DE), and the RNA quality was checked by running electrophoresis in RNA-denatured gels. All total RNA were stored at -20℃. For real-time quantitative RT-PCR, 1μg of total RNA were reverse-transcribed with reverse transcriptase and the excess RNA were digested E.coli RNase H to enhance the cDNA purity. The commercial Zebrafish 14K oligo microarray chip was obtained from Institute of Cellular and Organismic Biology at Academia Sinica and contained 14067 oligonucleotides represent 9666 unique genes with a redundancy of 31%. The detail oligonucleotide description can be obtained from Ocimun Biosolution (http://www.ocimumbio.com/web/default.asp). We used SuperScriptTM Indirect cDNA Labeling System kit (Invitrogen) to generate the fluorescently labeled probes. Total RNA isolated from WT and Tg(krt4:myrAkt1)cy18 were reversed transcribed into cDNA and coupling for Alexa Fluor 555 and Alexa Fluor 647 fluorescent dyes (Invitrogen), respectively. Before hybridization, the Zebrafish microarray chips were pretreated with 1% bovine serum albumin, 4X SCC, and 1% sodium dodecylsulfate (SDS) for 45min at 42℃, and then hybridized in SlideHybTM buffer (Ambion) for overnight at 42℃. After hybridization, chips were washed with 2X SSC and 0.5% SDS for 15min at 25℃ and finally with 0.5X SSC and 0.5% SDS for 15min at 25℃. The fluorescence intensities of Alexa Fluor 555 and Alexa Fluor 647 targets were scanned by Genepix scanner (Molecular Devices, Sunnyvale, CA, USA) and the acquired date were analyzed by Genepix and Genespring software (Aglient Technologies, Foster City, CA, USA).
