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Title: Identification of Pluripotency Genes in the Fish Medaka
Keywords: medaka, pluripotency, gene, early development, stem cell
Issue Date: 12-Aug-2011
Citation: WANG DANKE (2011-08-12). Identification of Pluripotency Genes in the Fish Medaka. ScholarBank@NUS Repository.
Abstract: Stem cell cultures can be derived directly from early developing embryos and indirectly from differentiated cells by forced expression of pluripotency transcription factors. Pluripotency genes are routinely used to characterize mammalian stem cell cultures at the molecular level. However, such genes have remained unknown in lower vertebrates. This study made use of the laboratory fish medaka as a model, because of its unique embryonic stem (ES) cells and sequenced genome as useful experimental tools and genetic resource. Seven medaka pluripotency genes were identified by homology search and expression in vivo and in vitro. By RT-PCR analysis, they fall into three groups of expression pattern. Group I includes nanog and oct4 showing gonad-specific expression; Group II contains sall4 and zfp281 displaying gonad-preferential expression; Group III has klf4, ronin and tcf3 exhibiting expression also in several somatic tissues apart from the gonads. The transcripts of the seven genes are maternally supplied and persist at a high level during early embryogenesis. Early embryos and adult gonads were used to examine expression in stem cells and differentiated derivatives by in situ hybridization. Strikingly, nanog and oct4 are highly expressed in pluripotent blastomeres of 16-cell embryos. In the adult testis, nanog expression was specific to spermatogonia, the germ stem cells, whereas tcf3 expression occurred in spermatogonia and differentiated cells. Most importantly, all the seven genes are pluripotency markers in vitro, because they showed high expression in undifferentiated ES cells but dramatic down-regulation upon differentiation. Therefore, these genes have conserved their pluripotency-specific expression in vitro from mammals to lower vertebrates. Furthermore, by using sequence differences between two medaka species: O. latipes and O. celebensis, I built a model to examine the timing of zygotic expression of six pluripotency genes by determining their expression from the paternal alleles. All those genes showed the onset of zygotic expression around the midblastula transition, suggesting their critical roles in early embryogenesis. Specifically, nanog and oct4 show earlier expression than the other remainder. Data obtained suggest the feasibility to study the hierarchical expression patterns of genes involved in pluripotency, cell fate decision and other processes.
Appears in Collections:Master's Theses (Open)

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