Production of transgenic triploid marine medaka (Oryzias dancena) carrying red fluorescence protein transgene driven by myosin light chain 2 promoter

Abstract

Triploidy was induced in the marine medaka (Oryzias dancena) by the cold shock treatment (0 °C) of fertilized eggs two minutes after fertilization for 30, 45, or 60 min. The triploid genotype was induced by all the thermal shock regimes tested. The best result was obtained when the eggs were treated for 45 min, which induced triploidy in all the resulting fish. Triploidy was confirmed with chromosomal and flow-cytometric analyses and erythrocyte measurements. The erythrocyte surface areas and volumes of the triploid fish were significantly larger, and their chromosome numbers (3N = 72) were 1.5 times greater than those of diploid fish (2N = 48). Based on a flow-cytometric analysis, the triploid fish had approximately 1.5 times the cellular DNA content (2.40 pg per cell) of the diploid specimens (1.61 pg per cell). Analysis of the gonads of one-year-old triploid fish showed that the induction of triploidy probably causes sterility in this species, and the effect was apparently greater in females than in males. Data from this study could provide the basis for the development of unique models for studying reproductive confinement in transgenic fish.