A transcriptional program underlying the circannual rhythms of gonadal development in medaka.

To cope with seasonal environmental changes, organisms have evolved approximately 1-y endogenous circannual clocks. These circannual clocks regulate various physiological properties and behaviors such as reproduction, hibernation, migration, and molting, thus providing organisms with adaptive advantages. Although several hypotheses have been proposed, the genes that regulate circannual rhythms and the underlying mechanisms controlling long-term circannual clocks remain unknown in any organism.

Neonatal malnutrition impacts fibroblast growth factor 21-induced neuron neurite outgrowth and growth hormone-releasing hormone secretion in neonatal mouse brain.

Neonatal malnutrition is one of the most common causes of neurological disorders. However, the mechanism of action of the factors associated with neonatal nutrition in the brain remains unclear. In this study, we focused on fibroblast growth factor (FGF) 21 to elucidate the effects of malnutrition on the neonatal brain.

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.

Genetic analysis of body weight in wild populations of medaka fish from different latitudes.

The genetic bases of growth and body weight are of economic and scientific interest, and teleost fish models have proven useful in such investigations. The Oryzias latipes species complex (medaka) is an abundant freshwater fish in Japan and suitable for genetic studies. We compared two wild medaka stocks originating from different latitudes.

Seasonal changes in NRF2 antioxidant pathway regulates winter depression-like behavior.

Seasonal changes in the environment lead to depression-like behaviors in humans and animals. The underlying mechanisms, however, are unknown. We observed decreased sociability and increased anxiety-like behavior in medaka fish exposed to winter-like conditions.

Action spectrum for photoperiodic control of thyroid-stimulating hormone in Japanese quail (Coturnix japonica).

At higher latitudes, vertebrates exhibit a seasonal cycle of reproduction in response to changes in day-length, referred to as photoperiodism. Extended day-length induces thyroid-stimulating hormone in the pars tuberalis of the pituitary gland. This hormone triggers the local activation of thyroid hormone in the mediobasal hypothalamus and eventually induces gonadal development.

Seasonal regulation of the lncRNA LDAIR modulates self-protective behaviours during the breeding season.

To cope with seasonal environmental changes, animals adapt their physiology and behaviour in response to photoperiod. However, the molecular mechanisms underlying these adaptive changes are not completely understood. Here, using genome-wide expression analysis, we show that an uncharacterized long noncoding RNA (lncRNA), LDAIR, is strongly regulated by photoperiod in Japanese medaka fish (Oryzias latipes).

Seasonal changes in color perception.

In temperate zones, organisms experience dynamic fluctuations in environment including changes in color. To cope with such seasonal changes in the environment, organisms adapt their physiology and behavior. Although color perception has been believed to be fixed throughout life, there is increasing evidence for the alteration in opsin gene expression induced by environmental stimuli in a number of animals.

Dynamic plasticity in phototransduction regulates seasonal changes in color perception.

To cope with seasonal changes in the environment, organisms adapt their physiology and behavior. Although color perception varies among seasons, the underlying molecular basis and its physiological significance remain unclear. Here we show that dynamic plasticity in phototransduction regulates seasonal changes in color perception in medaka fish.

Regulation of seasonal reproduction by hypothalamic activation of thyroid hormone.

Organisms living outside the tropics measure the changes in the length of the day to adapt to seasonal changes in the environment. Animals that breed during spring and summer are called long-day breeders, while those that breed during fall are called short-day breeders. Although the influence of thyroid hormone in the regulation of seasonal reproduction has been known for several decades, its precise mechanism remained unknown.

Endothelin receptor B2 (EDNRB2) is responsible for the tyrosinase-independent recessive white (mo(w) ) and mottled (mo) plumage phenotypes in the chicken.

A mutation that confers white plumage with black eyes was identified in the Minohiki breed of Japanese native chicken (Gallus gallus domesticus). The white plumage, with a few partially pigmented feathers, was not associated with the tyrosinase gene, and displayed an autosomal recessive mode of inheritance against the pigmented phenotype. All F1 offspring derived from crosses with mottled chickens (mo/mo), which show characteristic pigmented feathers with white tips, had plumage with a mottled-like pattern.

The medaka sex-determining gene DMY acquired a novel temporal expression pattern after duplication of DMRT1.

The male sex-determining gene, DMY, of the medaka is considered to have arisen via gene duplication of DMRT1. In the medaka, both genes are expressed in Sertoli cell lineage cells, but their temporal expression patterns are quite different. DMY expression starts just before the sex-determining period, whereas DMRT1 expression occurs during the testicular differentiation period.

Transgenic medaka enables easy oocytes detection in live fish.

Easy oocyte detection in living specimens benefits various developmental biology and environmental toxicology studies. One of the earliest markers of sex differentiation in medaka (Oryzias latipes) is oocyte development. Within the field of toxicology, a simple detection method for induced oocyte in the testis (testis-ova) as a result of endocrine disruption is necessary.

DMY gene induces male development in genetically female (XX) medaka fish.

Although the sex-determining gene SRY/Sry has been identified in mammals, homologues and genes that have a similar function have yet to be identified in nonmammalian vertebrates. Recently, DMY (the DM-domain gene on the Y chromosome) was cloned from the sex-determining region on the Y chromosome of the teleost fish medaka (Oryzias latipes). DMY has been shown to be required for the normal development of male individuals.

Interspecific hybridization between Oryzias latipes and Oryzias curvinotus causes XY sex reversal.

The teleost fish, Oryzias curvinotus, is a closely related species to the medaka, Oryzias latipes, and both species have the DMY gene, which is required for male development in O. latipes. It suggests that the molecular function of the DMY gene and the following molecular events of sex differentiation are conserved between these two species.

Wild-derived XY sex-reversal mutants in the Medaka, Oryzias latipes.

The medaka, Oryzias latipes, has an XX/XY sex-determination mechanism. A Y-linked DM domain gene, DMY, has been isolated by positional cloning as a sex-determining gene in this species. Previously, we found 23 XY sex-reversed females from 11 localities by examining the genotypic sex of wild-caught medaka.

The XX-XY sex-determination system in Oryzias luzonensis and O. mekongensis revealed by the sex ratio of the progeny of sex-reversed fish.

The sex-determining gene in Oryzias latipes and O. curvinotus has been proved to be DMY. Although O.

Mutations affecting gonadal development in Medaka, Oryzias latipes.

A gonad is formed from germ cells and somatic mesodermal cells through their interactions. Its development is coupled with the determination and differentiation of the sex and sex-associated traits. We carried out a large-scale screening of Medaka mutants in which gonadal development is affected.

Mutations affecting early distribution of primordial germ cells in Medaka (Oryzias latipes) embryo.

The development of germ cells has been intensively studied in Medaka (Oryzias latipes). We have undertaken a large-scale screen to identify mutations affecting the development of primordial germ cells (PGCs) in Medaka. Embryos derived from mutagenized founder fish were screened for an abnormal distribution or number of PGCs at embryonic stage 27 by RNA in situ hybridization for the Medaka vasa homologue (olvas).

A systematic genome-wide screen for mutations affecting organogenesis in Medaka, Oryzias latipes.

A large-scale mutagenesis screen was performed in Medaka to identify genes acting in diverse developmental processes. Mutations were identified in homozygous F3 progeny derived from ENU-treated founder males. In addition to the morphological inspection of live embryos, other approaches were used to detect abnormalities in organogenesis and in specific cellular processes, including germ cell migration, nerve tract formation, sensory organ differentiation and DNA repair.

DMY is a Y-specific DM-domain gene required for male development in the medaka fish.

Although the sex-determining gene Sry has been identified in mammals, no comparable genes have been found in non-mammalian vertebrates. Here, we used recombinant breakpoint analysis to restrict the sex-determining region in medaka fish (Oryzias latipes) to a 530-kilobase (kb) stretch of the Y chromosome. Deletion analysis of the Y chromosome of a congenic XY female further shortened the region to 250 kb.