Effect Of Simulated-microgravity On Zebrafish Embryonic Development And MicroRNA Expression

Space conditions are a complex set of phenomena involving multi-radiation, microgravity and weak magnetic field etc. Amongst all these phenomena, microgravity is a constant physical factor astronauts must meet during space flight. Therefore, the mechanism of microgravity-induced biological effects is one of the most important issues in space biological studies.In this paper, zebrafish (Danio rerio) embryos at different development stages were exposed to simulated microgravity, respectively, using a rotary cell culture system (RCCS) designed by National Aeronautics and Space Administration (NASA) of America. Biological effects of simulated microgravity on zebrafish embryos were investigated at the phenotypic and gene expression levels. Malformation rate and mortality rate were found increased after simulated microgravity exposure. Body length and heart rate were also increased during microgravity exposure and after a shot period of gravity recovery, but both returned to normal level after 10 days and 7 days of gravity recovery, respectively. At gene expression level, microRNA expression profiles of zebrafish embryos exposed to simulated-microgravity were analyzed using microarrays. Results demonstrated the microRNA expression profiles of zebrafish embryos varied, depending on the development stages of embyos exposed to simulated microgravity and the exposure time. All together, nine miRNAs showed significant changes after three different microgravity exposure (8-72hpf,24-72hpf and 24-48hpf), and were subsequently used in analysis of microRNA target and pathway prediction.The results of target prediction shows that, microRNA-204,-429 and-22a expression up-regulated, microRNA-16a expression down-regulated, as to their target gene sgcg was related to cardiomyocyte defects, muscular atrophy, and leading to arrhythmia, decline in cardiac function, increasing of heart rate of zebrafish under microgravity in this paper might be related to these microRNAs up-regulated. microRNA-738,-133b,-9* and-133a expression up-regulated, their target gene Nrarpa indirectly effects notch pathway and Wnt pathway. These two pathways are the significant mechanism about morphogenesis and development, therefore, whether incr- easing of malformation rate and mortality rate was related to this significant mechanism needs further studies.In addition, the mRNA expression levels of five differentially expressed proteins, obtained from our previous simulated-microgravity research, were analyzed using quantitative PCR (RT-qRCR). The five genes, inculding creatine kinase muscle a (ckmα), proteasome 26S subunit non-ATPase 8 (psmd8), actin alpha2 (αctα2), tubulin beta 2c(tubb2c) and prohibitin (prohibitin), displayed during different simulated-microgravity exposures, the mRNA expression levels of actin alpha2 (αctα2), tubulin beta 2c (tubb2c) and prohibitin (prohibitin) down-regulated, had the same trends to the proteins; the mRNA expression levels of creatine kinase muscle a (ckmα), proteasome 26S subunit non-ATPase 8 (psmd8) down-regulated, had different trends to the proteins. We supposed in the level of gene transcription and post-transcription translation existed regulated mechanism other molecular involved. However, whether this regulated mechanism was related to microRNA needs further studies.