Variation in responses to photoperiods and temperatures in Japanese medaka from different latitudes.

Seasonal changes are more robust and dynamic at higher latitudes than at lower latitudes, and animals sense seasonal changes in the environment and alter their physiology and behavior to better adapt to harsh winter conditions. However, the genetic basis for sensing seasonal changes, including the photoperiod and temperature, remains unclear. Medaka (Oryzias latipes species complex), widely distributed from subtropical to cool-temperate regions throughout the Japanese archipelago, provides an excellent model to tackle this subject.

Inter- and Intraspecific Variation in Sex Hormone-Induced Sex-Reversal in Medaka, and .

We compared sex-reversal ratios induced by 17α-methyltestosterone (MT) and 17β-estradiol (E2) exposure in two inbred medaka strains: Hd-rR derived from and HNI-II from . All MT exposures (0.2-25 ng mL) induced complete XX sex-reversal in HNI-II.

Centromere localization in medaka fish based on half-tetrad analysis.

Gene-centromere (G-C) mapping provides insight into vertebrate genome composition, structure and evolution. Although medaka fish are important experimental animals, no genome-wide G-C map of medaka has been constructed. In this study, we used 112 interspecific triploid hybrids and 152 DNA markers to make G-C maps of all 24 linkage groups (LGs).

Hyperosmotic tolerance of adult fish and early embryos are determined by discrete, single loci in the genus Oryzias.

The acquisition of environmental osmolality tolerance traits in individuals and gametes is an important event in the evolution and diversification of organisms. Although teleost fish exhibit considerable intra- and interspecific variation in salinity tolerance, the genetic mechanisms underlying this trait remain unclear. Oryzias celebensis survives in sea and fresh water during both the embryonic and adult stages, whereas its close relative Oryzias woworae cannot survive in sea water at either stage.

Estrogen alters gonadal soma-derived factor (Gsdf)/Foxl2 expression levels in the testes associated with testis-ova differentiation in adult medaka, Oryzias latipes.

Testis-ova differentiation in sexually mature male medaka (Oryzias latipes) is easily induced by estrogenic chemicals, indicating that spermatogonia persist in sexual bipotentiality, even in mature testes in medaka. By contrast, the effects of estrogen on testicular somatic cells associated with testis-ova differentiation in medaka remain unclear. In this study, we focused on the dynamics of sex-related genes (Gsdf, Dmrt1, and Foxl2) expressed in Sertoli cells in the mature testes of adult medaka during estrogen-induced testis-ova differentiation.