Sub-chronic and mild social defeat stress exposure to C57BL/6J mice increases visceral fat mass and causes accumulation of cholesterol and bile acids in the liver.

Major depressive disorder is accompanied by a high metabolic illness comorbidity and patients with atypical depression are a subgroup with particularly high risk of obesity, dyslipidemia, and metabolic syndrome; however, the underlying mechanisms have not been fully elucidated. In this study, we examined visceral fat deposition, lipid profiles in the liver, and gut microbiota in sub-chronic and mild social defeat stress (sCSDS)-exposed C57BL/6J mice, which exhibit atypical depression-like phenotypes, i.e., increased body weight and food and water intake. We found that visceral fat mass and levels of hepatic cholesterol and bile acids in sCSDS-exposed mice were significantly increased compared to those in controls. The expression of hepatic small heterodimer partner, a negative regulator of cholesterol metabolism, was significantly elevated in sCSDS-exposed mice. We also found that gut microbial diversity and composition including lower relative abundance of Bacteroides spp. and Bifidobacterium spp. in sCSDS-exposed mice were different from those in controls. In addition, relative abundance of Bacteroides spp. and Bifidobacterium spp. was significantly and negatively correlated with body weight, visceral fat mass, and hepatic cholesterol and bile acids levels. These results indicate that sCSDS-exposure induces dysbiosis, and thereby contributes to metabolic disorder development.

Properties of gene knockdown system by vector-based siRNA in zebrafish.

RNA interference (RNAi) has emerged as a powerful tool to silence specific genes. Vector-based RNAi systems have been developed to downregulate targeted genes in a spatially and temporally regulated fashion both in vitro and in vivo. The zebrafish (Danio rerio) is a model animal that has been examined based on a wide variety of biological techniques, including embryonic manipulations, forward and reverse genetics, and molecular biology. However, a heritable and tissue-specific knockdown of gene expression has not yet been developed in zebrafish. We examined two types of vector, which produce small interfering RNA (siRNA), the direct effector in RNAi system; microRNA (miRNA) process mimicking vectors with a promoter for RNA polymerase II and short hairpin RNA (shRNA) expressing vector through a promoter for RNA polymerase III. Though gene-silencing phenotypes were not observed in the miRNA process mimicking vectors, the transgenic embryos of the second vector (Tg(zU6-shGFP)), shRNA expressing vector for enhanced green fluorescence protein, revealed knockdown of the targeted gene. Interestingly, only the embryos from Tg(zU6-shGFP) female but not from the male fish showed the downregulation. Comparison of the quantity of siRNA produced by each vector indicates that the vectors tested here induced siRNA, but at low levels barely sufficient to silence the targeted gene.

A heat-inducible CRE/LOXP gene induction system in medaka.

We established three lines of transgenic medaka, a heat-shock element (HSE) monitor line (hse-GFP line), heat-inducible driver lines (hse-cre lines), and effector lines (gapdh-loxP[DsRed]-GFP lines). We employed these to comprehensively analyze gene induction at different time points in various tissues. These analyses demonstrate a good response of synthetic HSEs by heat treatment during embryogenesis and the mosaic gene induction by cre/loxP-mediated recombination, thus providing practical information regarding the feasibility of a heat-inducible cre/loxP-mediated system in medaka. We also activated recombination by local heat-treatment using a metal probe and an infrared laser. Our results collectively indicate that these lines allow us to perform lineage tracing and mosaic analysis and provide the platform to investigate gene functions at later developmental stage and adult.

Ovarian germline stem cells in the teleost fish, medaka (Oryzias latipes).

In the mammalian testis germline stem cells keep producing many sperms, while there is no direct evidence for the presence of germline stem cells in the ovary. It is widely accepted in mammals that the mature oocytes are supplied from a pool of primordial follicles in the adult ovary. In other vertebrates, such as fish, however, there has been no investigation on the mechanism underlying the high egg-producing ability. In this review, we introduce the recently identified ovarian germline stem cells and the surrounding unique structure in teleost fish, medaka (Oryzias latipes) [Nakamura S et al. Science. 2010; 328: 1561-1563]. We also discuss about the expression and function of sox9 that characterizes this unique structure.

Identification of germline stem cells in the ovary of the teleost medaka.

Germline stem cells continually produce sperm in vertebrate testes, whereas there is no direct evidence showing that germline stem cells are present in adult vertebrate ovaries. By using transgenic methods and clonal analysis, we identified germline stem cells that supported oogenesis and the production of offspring in the ovaries of adult medaka fish. Early-stage germ cells were localized in clusters along interwoven threadlike cords of sox9b-expressing somatic cells (termed germinal cradles) where the germ cells developed. Germline stem cells gave rise to germ cells that divided to produce cysts, which then underwent cell death or separated to form follicles. Our results provide insight into the germline stem cell biology of medaka and provide a model system for studying vertebrate stem cell niches.

The National BioResource Project Medaka (NBRP Medaka): an integrated bioresource for biological and biomedical sciences.

Medaka (Oryzias latipes) is a small freshwater teleost fish that serves as a model vertebrate organism in various fields of biology including development, genetics, toxicology and evolution. The recent completion of the medaka genome sequencing project has promoted the use of medaka as a comparative and complementary material for research on other vertebrates such as zebrafish, sticklebacks, mice, and humans. The Japanese government has supported the development of Medaka Bioresources since 2002. The second term of the Medaka Bioresource Project started in 2007. The National Institute for Basic Biology and Niigata University were selected as the core organizations for this project. More than 400 strains including more than 300 spontaneous and induced mutants, 8 inbred lines, 21 transgenic lines, 20 medaka-related species and 66 wild stock lines of medaka are now being provided to the scientific community and educational non-profit organizations. In addition to these live fish, NBRP Medaka is also able to provide cDNA/EST clones such as full-length cDNA and BAC/fosmid clones covering 90% of the medaka genome. All these resources can be found on the NBRP Medaka website (http://shigen.lab.nig.ac.jp/medaka/), and users can order any resource using the shopping cart system. We believe these resources will facilitate the further use of medaka and help to promote new findings for this vertebrate species.

[Bacterial endopathalmitis caused by B streptococcus endocarditis].

BACKGROUND: Bacterial endophthalmitis is often caused by a shift in the primary focus of infection in the patient's body. It is a high risk disease that can cause the loss of sight. Bacterial endophthalmitis with infectious endocarditis is very rare in Japan. CASE: A fifty-three-year-old woman visited our clinic complaining of pain, fever, and visual impairment in her left eye. OBSERVATIONS: The patient's left eye was blind, and showed hapopyon in the anterior chamber. She was admitted to our hospital with a diagnosis of endophthalmitis. Medical treatment with antibiotics was carried out, but the inflammation in her left eye increased. Her left eye was enucleated, and group B Streptococcus was found in the vitreous specimen. Echocardiography demonstrated vegetation of the posterior mitral valve. The diagnosis was made of endophthalmitis due to infectious endocarditis. CONCLUSION: We report an endophthalmitis patient with infectious endocarditis caused by group B streptococcus, based on histopathological findings. This is the first such case reported in Japan.

Vitellogenin-immunohistochemistry in the liver and the testis of the medaka, Oryzias latipes, exposed to 17beta-estradiol and p-nonylphenol.

Vitellogenin (VTG) produced in male fish has been used for a biomarker to study endocrine disrupters. However, the characteristics of VTG produced in male fish have not been studied well. In this study, we investigated the localization of VTG in the liver and the testis of male medaka (Oryzias latipes) treated with 17beta-estradiol (E2) and p-nonylphenol (NP). The male fish were exposed to 1 microg/L E2 and 500 microg/L NP for 1-12 days. Control groups were kept in water including only vehicle. The frozen sections of the liver and the testis were stained with immunohistochemical methods using an antiserum against medaka VTG as the first antibody. In the E2 and NP treated liver, the hepatocytes showed immunoreactivity. In particular, the cytoplasm close to the cell membrane surrounding the sinusoids was strongly immunopositive. In the testis of both treatments, the interstitial tissues and the cells (spermatocytes) in the seminiferous tubules were immunopositive. The concentration of VTG became gradually higher in both tissues with longer treatments. These results suggest that germ cells in the testis treated with E2 and NP are able to incorporate and accumulate VTG.