• Fisheries and Aquatic Sciences
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• v.18 no.1
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• pp.73-80
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• 2015

To examine the interrelationship between transgenic insertion patterns and transgene expression profiles in established transgenic fish lines, four stable transgenic marine medaka Oryzias dancena germlines harboring ${\beta}$-actin regulator-driven RFP reporter constructs were selected. The established transgenic strains were characterized with regard to their transgenic genotypes (insertion pattern, concatemer formation, and transgene copy number based on genomic Southern blot hybridization and qPCR assay) and expression characteristics at the mRNA (qRT-PCR), protein (western blot), and phenotypic (fluorescent appearance) levels. From comparative examinations, it was found that transgenic expression at both the transcription and translation levels could be significantly downregulated in transgenic strains, potentially through methylation-mediated transgene silencing that was particularly associated with the formation of a long tail-to-head tandem concatemer in the chromosomal integration site(s). When this occurred, an inverse relationship between the transgene copy number and fluorescence intensity was observed in the resultant transgenic fish. However, with the other transgenic genotype, transgenic individuals with an identical Southern blot hybridization pattern, containing a tandem concatemer(s), had very different expression levels (highly robust vs. low expression strengths), which was possibly related to the differential epigenetic modifications and/or degrees of methylation. The concatemer-dependent downregulation of transgene activity could be induced in transgenic fish, but the overall pattern was strain-specific. Our data suggest that neither a low (or single) transgene copy number nor tandem transgene concatemerization is indicative of strong or silenced transgene expression in transgenic fish carrying a ubiquitous transgene. Hence, a sufficient number of transgenic lineages, with different genotypes, should be considered to ensure the establishment of the best-performance transgenic line(s) for practical applications.

• Fisheries and Aquatic Sciences
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• v.18 no.2
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• pp.183-193
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• 2015

Several transgenic marine medaka Oryzias dancena strains harboring a green fluorescent protein (GFP) reporter construct regulated by an endogenous ${\beta}$-actin promoter were established and their expression characteristics in relation to transgene copy numbers were examined in 21 transgene genotypes. Most of the transgenic strains displayed transgene insertion patterns typical of microinjection-mediated introduction of foreign DNA into fish embryos, characterized by the random integration of multiple transgene copies (ranging from 1 - 282 copies per cell), often accompanied by the formation of concatemer(s), as assessed by genomic Southern blot hybridization analysis and qPCR. Transgenic strains showed ubiquitous and continued temporal and spatial expression patterns of the transgenic GFP during most of their life cycle, from the embryonic stage to adulthood, enabling assessment of the expression pattern of the endogenous ${\beta}$-actin gene. However, a comparative evaluation of transgene copy numbers and expression levels showed that copy number-dependent expression, the stability of the ubiquitous distribution and expression efficiency per transgene copy varied among the transgenic strains. Fluorescence expression levels were positively correlated with absolute transgene copy numbers, whereas the expression efficiency per transgene copy was inversely related to the number of transgene integrant copies. Data from this study will guide the selection of potentially desirable transgenic strains with ubiquitous expression of a fluorescent transgene, not only in this marine medaka species but also in other related model fish species.