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At least 19 recordsLinked to original sources
PubMed1992

A highly repetitive interspersed sequence isolated from genomic DNA of the Medaka, Oryzias latipes, is conserved in three other related species within the genus Oryzias.

A highly repeated interspersed sequence (OLR1) was isolated from a genomic DNA library of the Medaka, Oryzias latipes. The OLR1 was about 160 base pairs (bp) in length. As judged from the results of colony hybridization experiments, OLR1 is one of the major repeated DNA sequences in the Medaka genome and is present in every 136 kb on average. Results of Southern and colony-hybridization analyses indicate that OLR1 is a small interspersed repetitive element (SINE). OLR1-related sequences were conserved in other three species (O. luzonensis, O. curvinotus, and O. mekongnensis) within the genus Oryzias as a repetitive sequence. These results lend support at the DNA level to the hypothesis that these four species form one group in the genus Oryzias, as has been suggested from an analysis of their karyotypes (Magtoon and Uwa, '85, Proc. Jpn. Acad., Ser. B, 61:157-160).

Animals↗
PubMed2006

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. In the present study, we obtained interspecific hybrids between O. curvinotus and O. latipes and demonstrated sex-reversed XY females in the hybrids. The incidence of sex-reversed females in F1 XY hybrids between O. curvinotus females and O. latipes males, and hybrids between O. latipes females and O. curvinotus males were 21% and 100%, respectively. These results indicate that DMY does not always determine maleness in hybrid fish even though it is able to specify normal male development on its native genetic background and suggest that there are some differences between DMY(latipes) and DMY(curvinotus) alleles. Appearance of XY females in F1 hybrids also suggests that an autosomal or X-liked gene(s) from the maternal species interferes in the function of the paternal DMY gene in the male-determining process of the hybrid fish. These hybrid fish would supply a new experimental approach for investigating the genetic and molecular pathway of testis determination and differentiation.

Animals↗
PubMed2004

Expression of guanylyl cyclase genes in medaka hybrids (Oryzias curvinotus x Oryzias latipes).

The Hong Kong-originated medaka fish Oryzias curvinotus expresses nine genes (OcGC1 approximately OcGC8 and OcGC-R2) for membrane guanylyl cyclases (membrane GCs) and three genes (OcGCS-alpha(1), OcGCS-alpha(2), and OcGCS-beta(1)) for soluble GC subunits. The deduced amino acid sequences of membrane GCs expressed in O. curvinotus were quite similar to those expressed in the Japanese medaka Oryzias latipes, including a novel membrane GC gene, OlGC8, first isolated and characterized in O. latipes. O. curvinotus was able to produce hybrids with O. latipes, irrespective of the direction of crossing, and the resulting hybrids expressed both maternal and paternal soluble GC subunit genes, suggesting the possibility of the formation of a chimeric heterodimer in the hybrids. However, in early embryogenesis of hybrids, the maternal soluble GC subunit genes were expressed earlier than the paternal soluble GC subunit genes, suggesting that the maternal soluble GC subunit genes interact more effectively with maternal effector molecules such as transcription factors than with those of paternal origin.

Amino Acid Sequence↗
PubMed2003

Experimental hybridization among Oryzias species. II. Karyogamy and abnormality of chromosome separation in the cleavage of interspecific hybrids between Oryzias latipes and O. javanicus.

In interspecific hybridization between Oryzias latipes and O. javanicus, all hybrid embryos failed to develop and died before hatching. Cytological examination of fertilization and early development was performed to discover the cause of lethal development. When O. latipes eggs were inseminated by sperm of O. javanicus, the cortical reaction was induced normally. Chromosomal material in the fertilized eggs was visualized using the DNA-specific fluorochrome Hoechst. The spermatozoon was capable of penetrating into the egg cytoplasm through the micropyle, and the sperm nucleus transformed to the male pronucleus. The female pronucleus that formed after extrusion of the second polar body migrated towards the male pronucleus. The female and the male pronuclei underwent DNA synthesis and encountered each other in the center of the blastodisc, fused with one another and formed a zygote nucleus before breakdown of the nuclear envelope. Metaphase chromosomes with electron dense chromatin regions were abnormally divided into each blastomere in cleavage. The abnormally separating chromatin masses were also labeled by BrdU. The abnormal separation resulting in partial loss of fragmented chromatin might be a cause of abortive development in the interspecific hybrids between O. latipes and O. javanicus.

Animals↗
PubMed2005

Molecular phylogeny of the medaka fishes genus Oryzias (Beloniformes: Adrianichthyidae) based on nuclear and mitochondrial DNA sequences.

The phylogenetic relationships among medaka fishes of 2 genera, Oryzias and Xenopoecilus, were studied using the nuclear tyrosinase and mitochondrial 12S and 16S rRNA genes. Of the 23 species currently described for these genera, 13 species of Oryzias and 2 species of Xenopoecilus were examined. The tree topologies obtained from the nuclear and mitochondrial data were consistent, indicating that Xenopoecilus is a polyphyletic genus nested within Oryzias. This result suggested the necessity for a systematic study and taxonomic revision of Xenopoecilus. The combined data analysis of all data partitions resulted in a well-resolved tree, with most internal branches supported by high statistical values. Based on our combined data phylogeny, we divided the Oryzias species into three major species groups, namely the latipes, javanicus, and celebensis groups. These three groups corresponded to the three chromosomal groups (biarmed, monoarmed, and fused chromosome groups) previously proposed from karyological analyses. The phylogeographic pattern suggests historical vicariance between Sulawesi Island and the continental shelf.

Animals↗
PubMed1989

Levels of fenitrothion in Oryzias eggs and the effects on hatchability.

Levels of MEP in Oryzias eggs and the effects of MEP on hatchability were investigated. When Oryzias eggs were exposed to MEP-containing water, the eggs contained more MEP the higher the MEP concentration of the water, the more advanced the stage of development, and the longer the exposure. The MEP contents accumulated in the eggs were reduced to 2-19% after they were transferred to dechlorinated tap water for 96 h. There was a significant correlation between the MEP concentration in the water and the MEP content in the eggs. When Oryzias eggs in an early stage of development were exposed to 4 ppm MEP for 96 h or 64 ppm MEP for 6 h and were then placed in dechlorinated tap water until hatching, their hatching rates became significantly lower than those of the control, and abnormal fry occurred frequently. This experiment clarified that increases of MEP in Oryzias eggs were greatly affected by the MEP concentration in the water, and that the hatching rate was reduced and abnormal fry increased, even though the eggs contained the MEP only temporarily.

Animals↗
PubMed1998

Identification of the sex chromosomes of the medaka, Oryzias latipes, by fluorescence in situ hybridization.

In the medaka, Oryzias latipes, which does not have cytologically recognizable sex chromosomes, the sex is genetically determined and the mechanism of sex determination (XX/XY) can be revealed by genetic crosses using a particular pigment gene. In a previous study, we isolated a sex-linked DNA marker (SL1) using the genomic differences between inbred strains of medaka. In the present paper, we further isolated another sex-linked clone (pHO5.110). The pHO5. 110-related sequences were tightly linked to sex in O. latipes. We designated the locus of the pHO5.110-related sequence on sex chromosomes of medaka as Sex-Linked 2 (SL2). Southern blot analyses suggested that the pHO5.110-related sequence was tandemly repetitive in the medaka genome. Using the clone as a probe for FISH analysis, strong hybridization signals were obtained in a couple of chromosomes that formed one of two large submetacentric chromosome pairs. The pHO5.110-related sequences were repetitive in the genomes of other species of Oryzias (O. curvinotus, O. luzonensis and O. mekongensis) that are karyologically related to O. latipes (all are members of the so-called biarmed group). By contrast, the sequences were not detected as repetitive in other Oryzias species. Hence, it is thought that pHO5.110-related sequences were amplified in the genome of a common ancestor of the biarmed group.

Animals↗
PubMed1987

Mesodermal metamerism in the teleost, Oryzias latipes (the medaka).

Previous studies of the metameric pattern in mesodermal tissues of chick, mouse, turtle, and amphibian embryos have indicated that segmental characteristics exist along the entire length of the embryo. This paper describes this phenomenon in a fish embryo, for some differences in the cranial segmental plan exist between the anamniote and the amniote embryos hitherto studied. Embryos of the cyprinodont, Oryzias latipes, were fixed at various times, the examined by means of stereo scanning electron microscopy. As in other vertebrate embryos, the first indication of mesodermal metamerism in this fish embryo is the occurrence of somitomeres, which are orderly, tandemly arranged units of uncondensed mesenchymal cells in the paraxial mesoderm. As many as ten somitomeres can be observed caudal to the last formed somite to the elongating tail region. In addition, 7 somitomeres are present rostral to the first definitive somite, which is segment number eight. As in other vertebrate embryos examined, somitomeres in Oryzias embryos are circular, bilaminar arrays of paraxial mesoderm that form before any indications of segmentation can be seen with the light microscope. In the trunk region these mesodermal units condense to give rise to definitive somites, but in the head they eventually disperse. Despite a fundamentally different mode of gastrulation and a relatively small number of cells in the newly formed somitomeres, cranial segmentation in Oryzias embryos was found to be more similar in number to the metameric pattern of the embryos of the bird, reptile, and mammal than to the situation found in the two amphibians studied thus far.

Animals↗
PubMed2006

Temperature-dependent growth rates and gene expression patterns of various medaka Oryzias latipes cell lines derived from different populations.

Medaka Oryzias latipes has several geographically and genetically distinct populations. We examined temperature acclimation response in various medaka cell lines derived from different populations. Measurement of cell growth at various temperatures suggested that 15 degrees Celsius was the permissive growth temperature in all cell lines from the Northern Japanese and East Korean populations, but not in those from the Southern Japanese population and medaka-related species Oryzias celebensis, which inhabits a tropical zone. RT-PCR for 102 temperature-responsive genes, previously reported in other species, revealed that the accumulated mRNA level of a gene encoding HSP47 was lower at 25 degrees Celsius than at 33 degrees Celsius, and vice versa for 12 genes including IkappaBalpha and Rab-1c, in OLHNI-1 cell line from the Northern Japanese population. Further analysis by real-time PCR demonstrated that the accumulated mRNA levels of IkappaBalpha and Rab-1c in OLHNI-1 and OLSOK-e7 cell lines from the East Korean population were increased when the culture temperature was shifted from 33 to 15 degrees Celsius, but not in OLHdrR-e3 cell line from the Southern Japanese population. Since IkappaBalpha and Rab-1c are related to the NFkappaB cascade and endoplasmic reticulum-to-Golgi transport, respectively, it is inferred that immune responses and intracellular transport are possibly critical to temperature adaptation for medaka.

Animals↗
PubMed1998

Expression domains of the medaka (Oryzias latipes) Ol-Gsh 1 gene are reminiscent of those of clustered and orphan homeobox genes.

Screening of a medaka (Oryzias latipes) adult brain cDNA library, with a degenerated probe corresponding to the most conserved region of helix III of the homeodomain, led to the isolation of a gene homologous to a murine orphan Hox gene, named Gsh-1. We have called this gene Ol-Gsh 1 (Oryzias latipes-Gsh 1). Molecular analysis of the Ol-Gsh 1 putative protein points to potential functional domains which are highly conserved between fish and mouse genes. Whole-mount in situ hybridization shows that Ol-Gsh 1 is expressed in several waves during embryonic development. Transcripts are found in many regions of the central nervous system: the spinal cord, dorsal rhombencephalon, optic tectum, dorsal diencephalon, hypothalamus anlagen and rostral telencephalon. This multimodal expression pattern, strikingly conserved between fish and mammals, is reminiscent of both clustered and orphan homeobox genes. In addition, each expression wave is initiated in the fish embryo earlier than in the mammalian embryo, relative to the time scale defined by somitogenesis. We propose that Ol-Gsh 1 may be involved in conserved developmental pathways and in particular may be linked to proliferation events. Mouse Gsh-1 was shown to participate in neuro-endocrine functions of the hypothalamus. From late developmental stages onwards, Ol-Gsh 1 expression is also restricted to the hypothalamus. The expression pattern in this structure raises interesting questions concerning a fully or partially conserved function for these genes.

Amino Acid Sequence↗
PubMed1994

Relationship between the induction of proteins in the HSP70 family and thermosensitivity in two species of Oryzias (Pisces).

A cultured fish cell line, CE, derived from Oryzias celebensis, which lives in a tropical zone, was more heat-resistant than the OL32, which were derived from the Japanese medaka, Oryzias latipes which lives in a temperate zone. Protein synthesis in OL32 cells was also more heat-sensitive than that in CE cells. The relative levels in proteins of the HSP70 family and the ability of cells to tolerate severe heat treatment after a conditioning heat treatment were examined. Twenty-four hours after conditioning heat treatment, both cell lines retained thermotolerance even though three proteins in the HSP70 family had returned to their control levels.

Animals↗
PubMed1999

Identification of the Tol2 transposase of the medaka fish Oryzias latipes that catalyzes excision of a nonautonomous Tol2 element in zebrafish Danio rerio.

The Tol2 element is found in the genome of the medaka fish, Oryzias latipes, and contains DNA sequences similar to those of transposons of the hAT family. Previously, we have developed a transient embryonic excision assay in zebrafish, in which zebrafish embryos were injected with a plasmid DNA harboring the Tol2 element, and have shown that the Tol2 element is excisable from the injected plasmid DNA (Kawakami, K., Koga, A., Hori, H., Shima, A., 1998. Excision of the Tol2 transposable element of the medaka fish, Oryzias latipes, in zebrafish, Danio rerio. Gene 225, 17-22). Although the Tol2 element is thought to be autonomous, an active transposase encoded by the Tol2 element has not been identified. Here we report the identification and analysis of mRNA transcribed from the Tol2 element in zebrafish embryos. The Tol2 transcript has the capacity to encode a protein of 649 amino acids, whose amino acid sequence is similar to those of transposases of the hAT family. To determine whether the transcript encodes an active enzyme, we developed a novel transient embryonic excision assay in which zebrafish fertilized eggs were co-injected with RNA transcribed in vitro using the Tol2 cDNA as a template and a plasmid DNA harboring a nonautonomous Tol2 element, which has a deletion in the transposase coding region. The nonautonomous Tol2 element could be efficiently excised in the zebrafish only when co-injected with the Tol2 RNA. This result indicates that the Tol2 transcript encodes an active enzyme, a probable transposase, that can catalyze the excision reaction in trans. Further, by the co-injection analysis, we found that the Tol2 sequence lacking the first intron sequence of the transposase gene could not be excised, suggesting that it may contain essential cis-elements.

Amino Acid Sequence↗
PubMed2002

Sex determination and sex chromosome evolution in the medaka, Oryzias latipes, and the platyfish, Xiphophorus maculatus.

The first vertebrate master sex-determining gene different from Sry has been very recently discovered in a small aquarium fish, the medaka (Oryzias latipes). In this fish, the X and Y chromosomes apparently differ only by a 250-kb Y-specific region containing dmrt1bY (also called DMY and dmrt1Y), a male-specific copy of the autosomal gene dmrt1. Dmrt1 is a putative transcription factor probably involved in testis formation in different vertebrate lineages. Dmrt1bY is the only gene having escaped the drastic process of degeneration that devastated the small Y-specific region of the medaka. Mutations leading to truncation or lower expression of dmrt1bY result in XY male-to-female sex reversal. Hence, both genetic and functional evidences converge in making dmrt1bY an outstanding candidate for the function of a master sex-determining gene in fish. Nevertheless, dmrt1bY could not be detected in certain other Oryzias species or in more divergent fishes. Phylogenetic analysis revealed that the duplication of the autosomal dmrt1 that formed dmrt1bY is young in evolutionary terms. Hence, dmrt1bY is not the universal master sex-determining gene in fish. Because the classical fish models, such as zebrafish and pufferfish, are not very adequate to study the basis of genetic sex determination, alternative models, such as the platyfish (Xiphophorus maculatus), are re-emerging. In this fish, which is a well-suited laboratory organism, gene loci involved in pigmentation, melanoma formation, and sexual maturity have been mapped close to the master sex-determining gene. Interestingly, the platyfish can harbor three different sex chromosomes (W, X, and Y) in certain natural populations. Bacterial artificial chromosome contigs covering the sex-determining region of the platyfish are already available, and the positional cloning of the master sex-determining gene(s) should provide new insights into sex determination and sex chromosome evolution in fish and other vertebrates.

Amino Acid Sequence↗
PubMed1995

Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias.

cDNA corresponding to two hsp70-related genes (OLHSC70 and CEHSC70) were isolated from two lines of cultured fish cells derived from the genus Oryzias. OLHSC70 was 2,261 bp in length and encoded a protein of 686 amino acids with a predicted molecular mass of 76,120 daltons. CEHSC70 was 2,114 bp in length and it lacked the 5' region found in OLHSC70. Two-dimensional electrophoresis revealed that Oryzias latipes has at least three heat-inducible proteins with molecular masses of about 70,000 daltons. One of these proteins (Hsp70.1) was barely expressed under normal conditions but its high-level expression was induced by hyperthermia. The other two proteins (Hsc70.1, and Hsc70.2) were constitutively expressed under normal conditions and only slightly enhanced levels were induced by hyperthermia. Transfection with the cloned sequence, RNA dot-blot analysis and the two-dimensional electrophoresis of proteins showed that OLHSC70 encoded Hsc70.1.

Amino Acid Sequence↗
PubMed2006

Evolution of different Y chromosomes in two medaka species, Oryzias dancena and O. latipes.

Although the sex-determining gene DMY has been identified on the Y chromosome in the medaka (Oryzias latipes), this gene is absent in most Oryzias species, suggesting that closely related species have different sex-determining genes. Here, we investigated the sex-determination mechanism in O. dancena, which does not possess the DMY gene. Since heteromorphic sex chromosomes have not been reported in this species, a progeny test of sex-reversed individuals produced by hormone treatment was performed. Sex-reversed males yielded all-female progeny, indicating that O. dancena has an XX/XY sex-determination system. To uncover the cryptic sex chromosomes, sex-linked DNA markers were screened using expressed sequence tags (ESTs) established in O. latipes. Linkage analysis of isolated sex-linked ESTs showed a conserved synteny between the sex chromosomes in O. dancena and an autosome in O. latipes. Fluorescence in situ hybridization (FISH) analysis of these markers confirmed that sex chromosomes of these species are not homologous. These findings strongly suggest an independent origin of sex chromosomes in O. dancena and O. latipes. Further analysis of the sex-determining region in O. dancena should provide crucial insights into the evolution of sex-determination mechanisms in vertebrates.

Animals↗
PubMed2002

Diverse adaptability in oryzias species to high environmental salinity.

The genus Oryzias containing freshwater (FW) and seawater (SW) species is a potential model for studying mechanisms of osmotic adaptation. In this study, we compared SW adaptability of four Oryzias species, O. javanicus, O. dancena, O. latipes and O. marmoratus inhabiting different osmotic environments. SW adaptability was evaluated at several stages of the lifecycle: (i) survival rates of adult fish after transfer from FW to 50%SW or SW, (ii) spawning ability in FW and SW, (iii) fertilization rates in FW and SW, and (iv) hatching rates in FW, 50%SW and SW. Results obtained agreed with the natural habitat of each species: O. javanicus, which inhabits SW or brackish water (BW), is fully adaptable to both SW and FW at all the stages examined. The BW species O. dancena also revealed high SW adaptability except for the hatching rate. O. marmoratus, confined in FW, exhibited low SW adaptability at all stages examined while O. latipes, another FW species, was adaptable to SW at most stages examined. Based on these results, the role of SW adaptability to the distribution area of each species is discussed.

Adaptation, Physiological↗
PubMed2004

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. curvinotus has the DMY gene on the Y chromosome which is homologous to the Y chromosome of O. latipes, the sex-determining mechanism of other Oryzias fishes has not been identified. In order to uncover the sex-determining mechanism of O. luzonensis and O. mekongensis, which are most closely related species to O. latipes and O. curvinotus, we analyzed the sex ratio of the progeny of sex-reversed fish. We were able to obtain sex-reversed males by the administration of methyltestosterone, and found that these yielded all-female offspring in both species. These results indicate that O. luzonensis and O. mekongensis have the XX-XY sex-determination system.

Animals↗
PubMed1993

Structural studies of a novel type of tetraantennary sialoglycan unit in a carbohydrate-rich glycopeptide isolated from the fertilized eggs of Indian Medaka fish, Oryzias melastigma.

A novel carbohydrate-rich sialoglycopolyprotein of apparent molecular mass approximately 7000 Da was isolated from the fertilized eggs of the Medaka fish species, Oryzias melastigma. The glycoprotein was identified as a member of the L-hyosophorin family because it exhibited the following several distinctive features of L-hyosophorin molecules: (a) it contains a high proportion of carbohydrate (90% by weight), and (b) the amino acid sequence of the apopeptide was identical with that of the Oryzias latipes L-hyosophorin which has previously been demonstrated to be derived from a high molecular weight form of hyosophorin, i.e. H-hyosophorin, present in the cortical vesicles of unfertilized eggs. The apoprotein of H-hyosophorin is composed of tandem repeats of the L-hyosophorin apopeptide, i.e. it is a polyprotein. The structure of the carbohydrate portion of purified L-hyosophorin of O. melastigma was studied by composition and methylation analysis, selective chemical (periodate-Smith degradation; hydrazinolysis-nitrous acid deamination), and enzymatic (endo-beta-galactosidase; peptide:N-glycanase) degradation, together with instrumental methods (fast atom bombardment-mass spectrometry and 1H NMR). O. melastigma L-hyosophorin was found to contain two types of large, branched tetraantennary glycan units capped with sialic acids. The two glycans differ with respect to the branching pattern of the trimannosyl core (x = 4 or 6 in Eq. A). [formula: see text] The possible physiological significance of the hyosophorin family is discussed in the light of their unique structural features.

Animals↗