Congenital anaemia associated with loss-of-function variants in DNA polymerase epsilon 1

DNA polymerase epsilon (Pol ε), a component of the core replisome, is involved in DNA replication. Although genetic defects of Pol ε have been reported to cause immunodeficiency syndromes, its role in haematopoiesis remains unknown. Here, we identified compound heterozygous variants (p.[Asp1131fs];[Thr1891del]) in POLE, encoding Pol ε catalytic subunit A (POLE1), in siblings with a syndromic form of severe congenital transfusion-dependent anaemia. In contrast to Diamond-Blackfan anaemia, marked reticulocytopenia or marked erythroid hypoplasia was not found. Their bone marrow aspirates during infancy revealed erythroid dysplasia with strongly positive TP53 in immunostaining. Repetitive examinations demonstrated trilineage myelodysplasia within 2 years from birth. They had short stature and facial dysmorphism. HEK293 cell-based expression experiments and analyses of patient-derived induced pluripotent stem cells (iPSCs) disclosed a reduced mRNA level of Asp1131fs-POLE1 and defective nuclear translocation of Thr1891del-POLE1. Analysis of iPSCs showed compensatory mRNA upregulation of the other replisome components and increase of the TP53 protein, both suggesting dysfunction of the replisome. We created Pole-knockout medaka fish and found that heterozygous fishes were viable, but with decreased RBCs. Our observations expand the phenotypic spectrum of the Pol ε defect in humans, additionally providing unique evidence linking Pol ε to haematopoiesis.

Spatio-temporal control of targeted gene expression in combination with CRISPR/Cas and Tet-On systems in Medaka

Spatial and temporal control of transgene expression is a powerful approach to understand gene functions in specific cells and tissues. The Tet-On system is a robust tool for controlling transgene expression spatially and temporally; however, few studies have examined whether this system can be applied to postembryonic stages of Medaka (Oryzias latipes) or other fishes. Here, we first improved a basal promoter sequence on the donor vector for a nonhomologous end joining (NHEJ)-based knock-in (KI) system. Next, using transgenic Medaka for establishing the Tet-On system by KI, we demonstrated that doxycycline administration for four or more days by feeding can be a stable and efficient method to achieve expression of the transduced reporter gene in adult fish. From these analyses, we propose an optimized approach for a spatio-temporal gene-expression system in the adult stage of Medaka and other small fishes.

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. Here, we show a transcriptional program underlying the circannual clock in medaka fish (Oryzias latipes). We monitored the seasonal reproductive rhythms of medaka kept under natural outdoor conditions for 2 y. Linear regression analysis suggested that seasonal changes in reproductive activity were predominantly determined by an endogenous program. Medaka hypothalamic and pituitary transcriptomes were obtained monthly over 2 y and daily on all equinoxes and solstices. Analysis identified 3,341 seasonally oscillating genes and 1,381 daily oscillating genes. We then examined the existence of circannual rhythms in medaka via maintaining them under constant photoperiodic conditions. Medaka exhibited approximately 6-mo free-running circannual rhythms under constant conditions, and monthly transcriptomes under constant conditions identified 518 circannual genes. Gene ontology analysis of circannual genes highlighted the enrichment of genes related to cell proliferation and differentiation. Altogether, our findings support the "histogenesis hypothesis" that postulates the involvement of tissue remodeling in circannual time-keeping.

Behavioral photosensitivity of multi-color-blind medaka: enhanced response under ultraviolet light in the absence of short-wavelength-sensitive opsins

BACKGROUND

The behavioral photosensitivity of animals could be quantified via the optomotor response (OMR), for example, and the luminous efficiency function (the range of visible light) should largely rely on the repertoire and expression of light-absorbing proteins in the retina, i.e., the opsins. In fact, the OMR under red light was suppressed in medaka lacking the red (long-wavelength sensitive [LWS]) opsin.

RESULTS

We investigated the ultraviolet (UV)- or blue-light sensitivity of medaka lacking the violet (short-wavelength sensitive 1 [SWS1]) and blue (SWS2) opsins. The sws1/sws2 double or sws1/sws2/lws triple mutants were as viable as the wild type. The remaining green (rhodopsin 2 [RH2]) or red opsins were not upregulated. Interestingly, the OMR of the double or triple mutants was equivalent or even increased under UV or blue light (λ = 350, 365, or 450 nm), which demonstrated that the rotating stripes (i.e., changes in luminance) could fully be recognized under UV light using RH2 alone. The OMR test using dichromatic stripes projected onto an RGB display consistently showed that the presence or absence of SWS1 and SWS2 did not affect the equiluminant conditions.

CONCLUSIONS

RH2 and LWS, but not SWS1 and SWS2, should predominantly contribute to the postreceptoral processes leading to the OMR or, possibly, to luminance detection in general, as the medium-wavelength-sensitive and LWS cones, but not the SWS cones, are responsible for luminance detection in humans.

High-speed system to generate congenic strains in medaka

The congenic strain, an inbred strain containing a small genomic region from another strain, is a powerful tool to assess the phenotypic effect of polymorphisms and/or mutations in the substituted genomic region. Recent substantial progress in the genetic studies of complex traits increases the necessity of congenic strains and, therefore, a quick breeding system for congenic strains has become increasingly important in model organisms such as mouse and medaka. Traditionally, more than ten generations are necessary to produce a congenic strain. In contrast, a quick method has been reported previously for the mouse, in which the use of genetic markers reduces the required number of backcross generations to about a half that of the traditional method, so that it would take around six generations to obtain a congenic strain. Here, we present an even quicker congenic production system, which takes only about four generations. The system can produce medaka congenic strains having part of the HNI-II (an inbred medaka strain derived from the northern Japanese population, Oryzias sakaizumii) genome in the HdrR-II1 (another inbred strain from the southern Japanese population, O. latipes) background. In this system, the availability of frozen sperm and genotype data of the BC1 male population makes it possible to start marker-assisted congenic production after obtaining the BC2 population. Our evaluation revealed that the system could work well to increase the percentage of recipient genome as expected, so that a congenic strain may be obtained in about one year.

Ghost introgression in ricefishes of the genus Adrianichthys in an ancient Wallacean lake

Because speciation might have been promoted by ancient introgression from an extinct lineage, it is important to detect the existence of 'ghost introgression' in focal taxa and examine its contribution to their diversification. In this study, we examined possible ghost introgression and its contributions to the diversification of ricefishes of the genus Adrianichthys in Lake Poso, an ancient lake on Sulawesi Island, in which some extinctions are known to have occurred. Population-genomic analysis revealed that two extant Adrianichthys species, A. oophorus and A. poptae are reproductively isolated from each other. Comparisons of demographic models demonstrated that introgression from a ghost population, which diverged from the common ancestor of A. oophorus and A. poptae, is essential for reconstructing the demographic history of Adrianichthys. The best model estimated that the divergence of the ghost population greatly predated the divergence between A. oophorus and A. poptae, and that the ghost population secondarily contacted the two extant species within Lake Poso more recently. Genome scans and simulations detected a greatly divergent locus, which cannot be explained without ghost introgression. This locus was also completely segregated between A. oophorus and A. poptae. These findings suggest that variants that came from a ghost population have contributed to the divergence between A. oophorus and A. poptae, but the large time-lag between their divergence and ghost introgression indicates that the contribution of introgression may be restricted.

A gene regulatory network combining Pax3/7, Sox10 and Mitf generates diverse pigment cell types in medaka and zebrafish

Neural crest cells generate numerous derivatives, including pigment cells, and are a model for studying how fate specification from multipotent progenitors is controlled. In mammals, the core gene regulatory network for melanocytes (their only pigment cell type) contains three transcription factors, Sox10, Pax3 and Mitf, with the latter considered a master regulator of melanocyte development. In teleosts, which have three to four pigment cell types (melanophores, iridophores and xanthophores, plus leucophores e.g. in medaka), gene regulatory networks governing fate specification are poorly understood, although Mitf function is considered conserved. Here, we show that the regulatory relationships between Sox10, Pax3 and Mitf are conserved in zebrafish, but the role for Mitf is more complex than previously emphasized, affecting xanthophore development too. Similarly, medaka Mitf is necessary for melanophore, xanthophore and leucophore formation. Furthermore, expression patterns and mutant phenotypes of pax3 and pax7 suggest that Pax3 and Pax7 act sequentially, activating mitf expression. Pax7 modulates Mitf function, driving co-expressing cells to differentiate as xanthophores and leucophores rather than melanophores. We propose that pigment cell fate specification should be considered to result from the combinatorial activity of Mitf with other transcription factors.

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. In this study, we examined the critical photoperiods and critical temperatures required for seasonal gonadal development in female medaka from local populations at various latitudes. Intraspecific differences in critical photoperiods and temperatures were detected, demonstrating that these differences were genetically controlled. Most medaka populations could perceive the difference between photoperiods for at least 1 h. Populations in the Northern Japanese group required 14 h of light in a 24 h photoperiod to develop their ovaries, whereas ovaries from the Southern Japanese group developed under 13 h of light. Additionally, Miyazaki and Ginoza populations from lower latitudes were able to spawn under short-day conditions of 11 and 10 h of light, respectively. Investigation of the critical temperature demonstrated that the Higashidori population, the population from the northernmost region of medaka habitats, had a critical temperature of over 18 °C, which was the highest critical temperature among the populations examined. The Miyazaki and the Ginoza populations, in contrast, were found to have critical temperatures under 14 °C. When we conducted a transplant experiment in a high-latitudinal environment using medaka populations with different seasonal responses, the population from higher latitudes, which had a longer critical photoperiod and a higher critical temperature, showed a slower reproductive onset but quickly reached a peak of ovarian size. The current findings show that low latitudinal populations are less responsive to photoperiodic and temperature changes, implying that variations in this responsiveness can alter seasonal timing of reproduction and change fitness to natural environments with varying harshnesses of seasonal changes. Local medaka populations will contribute to elucidating the genetic basis of seasonal time perception and adaptation to environmental changes.

Live imaging of nitric oxide release in vascular endothelial cells in response to mechanical stimuli on an organ chip

Background

Nitric oxide (NO), released from vascular endothelial cells in response to mechanical stimuli, regulates cardiac contractility and are also involved in the prevention of the development of cardiac hypertrophy.

Purpose

To establish an experimental system for live observation of NO release in response to mechanical stimuli on an organ chip.

Methods

Organ chips, which we used for the development of a heart-on-a-chip in the previous study [1], were used.

We seeded 300,000 human umbilical vein endothelial cells on a stretchable elastic membrane coated with Matrigel of a chip channel. Shear stress was applied to the cells by increasing flow rate of a peristaltic pump connected to the chip channel (Figure 1A). Pressure stimulus was applied by hydrostatic pressure. Stretch stimulus was applied by suction to the side ports of a chip using an electric syringe pump (Figure 1B). Cells were stained with 10 μM 4,5-diaminofluorescein diacetate for fluorescent live NO imaging.

Results

Monolayers of the endothelial cells formed intercellular junctions confirmed by CD31 staining (Figure 1C, yellow). Apparent permeability, which was measured by Texas red dye (MW 3000), was maintained at a low level of ∼3x10–6 cm/s until day 30, suggested the formation of robust intercellular junction.

When the endothelial cells were subjected to a pressure stimulus of 60 mmHg for 60 s, NO release was observed that lasted for >2 minutes (Figure 2A). A peak value of 1.46±1.08 (mean ± standard deviation) times the baseline was observed 271 s after the beginning of the pressure stimulus (n=251 cells). When the cells were subjected to a 1% stretch for 60 s, a peak value of 1.29±0.33 times the baseline was observed 105 s after the beginning of the stretch stimulus (Figure 2B). A shear stress of 0.01 dyn/cm2 hardly increased NO release (1.20±0.27 times the baseline, Figure 2C).

Conclusion

The system for live NO imaging in vascular endothelial cells in response to mechanical stimuli was established using organ-on-a-chip. The heart-on-a-chip with endothelial cells will be useful in elucidating the effects of mechanical stimulus such as hypertension on the contractile function and the remodeling of the heart.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science

Genomic variations and epigenomic landscape of the Medaka Inbred Kiyosu-Karlsruhe (MIKK) panel

BACKGROUND

The teleost medaka (Oryzias latipes) is a well-established vertebrate model system, with a long history of genetic research, and multiple high-quality reference genomes available for several inbred strains. Medaka has a high tolerance to inbreeding from the wild, thus allowing one to establish inbred lines from wild founder individuals.

RESULTS

We exploit this feature to create an inbred panel resource: the Medaka Inbred Kiyosu-Karlsruhe (MIKK) panel. This panel of 80 near-isogenic inbred lines contains a large amount of genetic variation inherited from the original wild population. We use Oxford Nanopore Technologies (ONT) long read data to further investigate the genomic and epigenomic landscapes of a subset of the MIKK panel. Nanopore sequencing allows us to identify a large variety of high-quality structural variants, and we present results and methods using a pan-genome graph representation of 12 individual medaka lines. This graph-based reference MIKK panel genome reveals novel differences between the MIKK panel lines and standard linear reference genomes. We find additional MIKK panel-specific genomic content that would be missing from linear reference alignment approaches. We are also able to identify and quantify the presence of repeat elements in each of the lines. Finally, we investigate line-specific CpG methylation and performed differential DNA methylation analysis across these 12 lines.

CONCLUSIONS

We present a detailed analysis of the MIKK panel genomes using long and short read sequence technologies, creating a MIKK panel-specific pan genome reference dataset allowing for investigation of novel variation types that would be elusive using standard approaches.

The Medaka Inbred Kiyosu-Karlsruhe (MIKK) panel

Background

Unraveling the relationship between genetic variation and phenotypic traits remains a fundamental challenge in biology. Mapping variants underlying complex traits while controlling for confounding environmental factors is often problematic. To address this, we establish a vertebrate genetic resource specifically to allow for robust genotype-to-phenotype investigations. The teleost medaka (Oryzias latipes) is an established genetic model system with a long history of genetic research and a high tolerance to inbreeding from the wild.

Results

Here we present the Medaka Inbred Kiyosu-Karlsruhe (MIKK) panel: the first near-isogenic panel of 80 inbred lines in a vertebrate model derived from a wild founder population. Inbred lines provide fixed genomes that are a prerequisite for the replication of studies, studies which vary both the genetics and environment in a controlled manner, and functional testing. The MIKK panel will therefore enable phenotype-to-genotype association studies of complex genetic traits while allowing for careful control of interacting factors, with numerous applications in genetic research, human health, drug development, and fundamental biology.

Conclusions

Here we present a detailed characterization of the genetic variation across the MIKK panel, which provides a rich and unique genetic resource to the community by enabling large-scale experiments for mapping complex traits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02623-z.

Diversity of lateral line patterns and neuromast numbers in the genus Oryzias

A remarkable diversity of lateral line patterns exists in adult teleost fishes, the basis of which is largely unknown. By analysing the lateral line patterns and organ numbers in 29 Oryzias species and strains we report a rapid diversification of the lateral line system within this genus. We show a strong dependence of lateral line elaboration (number of neuromasts per cluster, number of parallel lateral lines) on adult species body size irrespective of phylogenetic relationships. In addition, we report that the degree of elaboration of the anterior lateral line, posterior lateral line and caudal neuromast clusters is tightly linked within species, arguing for a globally coordinated mechanism controlling lateral line organ numbers and patterns. We provide evidence for a polygenic control over neuromast numbers and positioning in the genus Oryzias. Our data also indicate that the diversity in lateral lines can arise as a result of differences in patterning both during embryonic development and post-embryonically, where simpler embryonic patterns generate less complex adult patterns and organ numbers, arguing for a linkage between the two processes.

Development of a human heart-on-a-chip model using induced pluripotent stem cells, fibroblasts and endothelial cells

Background

The use of animal models in cardiovascular research is associated with two serious, intrinsic problems: inaccuracy in the extrapolation of data obtained from animals such as rodents due to different cardiac physiology and animal ethics.

Purpose

To develop an artificial human heart model for cardiovascular research using organ-on-a-chip technology and human cells

Methods

Organ chips made of silicone (polydimethylsiloxane) that have two microfluidic channels, a top channel and a bottom channel, separated by a 50-μm thick membrane with 7-μm pores hexagonally packed at 40-μm intervals (Figure 1), were used in this study.

We seeded 10,000 human umbilical vein endothelial cells on the membrane surface in the bottom channel to mimic the vasculature. Next, we seeded a mixture of 100,000 human-induced pluripotent stem cells (hiPSCs) and 50,000 human gingival fibroblasts on the membrane surface in the top channel (Figure 1). Human gingival fibroblasts facilitate cardiac differentiation of hiPSCs [1]. We performed the cardiac differentiation of hiPSCs using a previously described protocol [1]. Culture medium was perfused at a constant rate of 60 μl/h to maintain the culture.

Results

We observed spontaneous contraction of hiPSC-derived cardiomyocytes 20–26 days after the start of the differentiation protocol. Simultaneously, we conducted live intracellular calcium imaging using a fluorogenic calcium-sensitive dye, Cal-520 AM (5 μM in the culture medium). hiPSC-derived cardiomyocytes exhibited a periodic, coordinated pattern of calcium influx synchronised with their contraction under fluorescence microscopy (Figure 2A). Moreover, we found that the β-adrenergic agonist noradrenaline elevated the heart rate of hiPSC-derived cardiomyocytes on the organ chips in a dose-dependent manner (Figures 2A, B).

After observing the contraction and intracellular calcium influx of hiPSC-derived cardiomyocytes, we performed immunocytochemistry. Confocal microscopy indicated that the fluorescent signal obtained from anti-cardiac troponin T antibody staining in the top channel exhibited a typical striated pattern with 1.56±0.12-μm interval that reflected sarcomere structure (Figure 2C, yellow). Moreover, the fluorescent signal obtained from anti-CD31 antibody staining in the bottom channel exhibited a typical pattern at the boundary between cells, which is expected at the cell–cell junction of endothelial cells.

Conclusion

We developed a human heart-on-a-chip model that was confirmed by the functional response to noradrenaline and the histological evidence of sarcomere structure and vasculature, with a capability of live imaging. We expect that this model would be useful for examining the physiological function and for the pharmacological analysis of not only the normal heart but also the heart that reflects specific patient's pathophysiology using patient-derived hiPSCs.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science Figure 1Figure 2

Genome editing reveals fitness effects of a gene for sexual dichromatism in Sulawesian fishes

Sexual selection drives rapid phenotypic diversification of mating traits. However, we know little about the causative genes underlying divergence in sexually selected traits. Here, we investigate the genetic basis of male mating trait diversification in the medaka fishes (genus Oryzias) from Sulawesi, Indonesia. Using linkage mapping, transcriptome analysis, and genome editing, we identify csf1 as a causative gene for red pectoral fins that are unique to male Oryzias woworae. A cis-regulatory mutation enables androgen-induced expression of csf1 in male fins. csf1-knockout males have reduced red coloration and require longer for mating, suggesting that coloration can contribute to male reproductive success. Contrary to expectations, non-red males are more attractive to a predatory fish than are red males. Our results demonstrate that integrating genomics with genome editing enables us to identify causative genes underlying sexually selected traits and provides a new avenue for testing theories of sexual selection.

Dynamic transcriptional and chromatin accessibility landscape of medaka embryogenesis

Medaka (Oryzias latipes) has become an important vertebrate model widely used in genetics, developmental biology, environmental sciences, and many other fields. A high-quality genome sequence and a variety of genetic tools are available for this model organism. However, existing genome annotation is still rudimentary, as it was mainly based on computational prediction and short-read RNA-seq data. Here we report a dynamic transcriptome landscape of medaka embryogenesis profiled by long-read RNA-seq, short-read RNA-seq, and ATAC-seq. By integrating these data sets, we constructed a much-improved gene model set including about 17,000 novel isoforms and identified 1600 transcription factors, 1100 long noncoding RNAs, and 150,000 potential cis-regulatory elements as well. Time-series data sets provided another dimension of information. With the expression dynamics of genes and accessibility dynamics of cis-regulatory elements, we investigated isoform switching, as well as regulatory logic between accessible elements and genes, during embryogenesis. We built a user-friendly medaka omics data portal to present these data sets. This resource provides the first comprehensive omics data sets of medaka embryogenesis. Ultimately, we term these three assays as the minimum ENCODE toolbox and propose the use of it as the initial and essential profiling genomic assays for model organisms that have limited data available. This work will be of great value for the research community using medaka as the model organism and many others as well.

A key metabolic gene for recurrent freshwater colonization and radiation in fishes

Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene Fads2 in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of Fads2 in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in Fads2 copies, indicating its key role in freshwater colonization.

Transvaginal three-dimensional ultrasound assessment of Sylvian fissures at 18-30 weeks' gestation

OBJECTIVE

To (1) evaluate the normal development of the Sylvian fissures in the anterior coronal view of the fetal brain at 18-30 weeks' gestation by transvaginal three-dimensional (3D) ultrasound, (2) develop reference ranges of measurements of the right and left Sylvian fissure angles during normal pregnancy at 18-30 weeks' gestation, and (3) examine intra- and interobserver repeatability of measurements of the right and left Sylvian fissure angles.

METHODS

This was a prospective cross-sectional study of 422 women with a singleton pregnancy attending an ultrasound-based research clinic between March and December 2017. The entry criteria for the study were appropriately grown live fetus with no suspected structural and/or chromosomal defects between 18 + 0 and 30 + 6 weeks' gestation. Normal development of the Sylvian fissures was assessed in the anterior coronal plane of the fetal brain using transvaginal 3D volume multiplanar imaging. The coronal view was visualized as a single image from the three orthogonal views. Subsequently, the right and left Sylvian fissure angles were measured between a horizontal reference line (0°) and a line drawn along the upper side of the respective Sylvian fissure. Intra- and interobserver repeatability of the Sylvian fissure angle measurements was assessed by Bland-Altman plots. Reference equations were constructed for right and left Sylvian fissure angles for gestational age (GA) and head circumference (HC) using the Generalized Additive Models for Location Scale and Shape package.

RESULTS

In the anterior coronal view of the fetal brain, an inward rotation of the upper portion of the Sylvian fissures was observed during the second and third trimesters of pregnancy. There was a significant negative polynomial association between the Sylvian fissure angles and GA and HC. Both Sylvian fissure angles crossed the reference line (zero), going from positive to negative, at around 25 weeks' gestation or at HC of 22 cm. Z-score difference between the smoothed percentiles of the right and left Sylvian fissure angles indicated that median, 10^th and 90^th smoothed percentiles were closest and almost the same for the GA-based references between 18 and 28 weeks and for the HC-based references between 14 and 24 cm. The intraclass correlation coefficient of the right and left Sylvian fissure angle measurements between the two sonographers was excellent at 0.993 (95% CI, 0.988-0.996) and 0.991 (95% CI, 0.985-0.995), respectively. On Bland-Altman analysis, the mean difference between the two sonographers in right Sylvian fissure angle measurement was 0.4° (95% CI, -10.2 to 10.1°) and in left Sylvian fissure angle it was 1.0° (95% CI, -9.6 to 11.6°).

CONCLUSIONS

Assessment of the Sylvian fissure angles is highly reproducible. Sylvian fissure angle reference charts can serve as a screening tool for malformations of cortical development, guiding subsequent follow-up and referral for fetal brain magnetic resonance imaging and/or assessment by an expert neurosonologist. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Stem cell topography splits growth and homeostatic functions in the fish gill

While lower vertebrates contain adult stem cells (aSCs) that maintain homeostasis and drive un-exhaustive organismal growth, mammalian aSCs display mainly the homeostatic function. Here, we use lineage analysis in the medaka fish gill to address aSCs and report separate stem cell populations for homeostasis and growth. These aSCs are fate-restricted during the entire post-embryonic life and even during re-generation paradigms. We use chimeric animals to demonstrate that p53 mediates growth coordination among fate-restricted aSCs, suggesting a hierarchical organisation among lineages in composite organs like the fish gill. Homeostatic and growth aSCs are clonal but differ in their topology; modifications in tissue architecture can convert the homeostatic zone into a growth zone, indicating a leading role for the physical niche defining stem cell output. We hypothesise that physical niches are main players to restrict aSCs to a homeostatic function in animals with fixed adult size.

Histopathologic features of melanocytic tumors in Xiphophorus melanoma receptor kinase (xmrk)-transgenic medaka (Oryzias latipes)

Melanocytic tumors in Xiphophorus melanoma receptor kinase (xmrk)-transgenic Carbio and HB11A strains of medaka were examined histopathologically at 7 months post-hatching. Medaka of both strains developed melanocytic tumors with a penetrance of 100%. In both strains, neoplastic cells containing intracytoplasmic melanin pigment granules showed significant invasive growth patterns. In addition, epithelioid neoplastic cells were arranged in solid nests, and spindle neoplastic cells were arranged in interlacing streams and bundles. Nuclear atypia, anisokaryosis, cellular pleomorphism, and the appearance of anaplastic giant cells containing multiple nuclei or a single nucleus were observed in neoplastic lesions in both medaka strains. However, neither strain exhibited mitotic figures or invasion of blood vessels by neoplastic cells. Based on these histopathologic findings, the tumors were diagnosed as malignant melanoma. This is the first report of detailed histomorphologic characteristics of malignant melanoma in xmrk-transgenic medaka.

Abnormal nuclear morphology is independent of longevity in a zmpste24-deficient fish model of Hutchinson-Gilford progeria syndrome (HGPS)

Lamin is an intermediate protein underlying the nuclear envelope and it plays a key role in maintaining the integrity of the nucleus. A defect in the processing of its precursor by a metalloprotease, ZMPSTE24, results in the accumulation of farnesylated prelamin in the nucleus and causes various diseases, including Hutchinson-Gilford progeria syndrome (HGPS). However, the role of lamin processing is unclear in fish species. Here, we generated zmpste24-deficient medaka and evaluated their phenotype. Unlike humans and mice, homozygous mutants did not show growth defects or lifespan shortening, despite lamin precursor accumulation. Gonadosomatic indices, blood glucose levels, and regenerative capacity of fins were similar in 1-year-old mutants and their wild-type (WT) siblings. Histological examination showed that the muscles, subcutaneous fat tissues, and gonads were normal in the mutants at the age of 1 year. However, the mutants showed hypersensitivity to X-ray irradiation, although p53target genes, p21 and mdm2, were induced 6 h after irradiation. Immunostaining of primary cultured cells from caudal fins and visualization of nuclei using H2B-GFP fusion proteins revealed an abnormal nuclear shape in the mutants both in vitro and in vivo. The telomere lengths were significantly shorter in the mutants compared to WT. Taken together, these results suggest that zmpste24-deficient medaka phenocopied HGPS only partially and that abnormal nuclear morphology and lifespan shortening are two independent events in vertebrates.

Distinct interactions of Sox5 and Sox10 in fate specification of pigment cells in medaka and zebrafish

Mechanisms generating diverse cell types from multipotent progenitors are fundamental for normal development. Pigment cells are derived from multipotent neural crest cells and their diversity in teleosts provides an excellent model for studying mechanisms controlling fate specification of distinct cell types. Zebrafish have three types of pigment cells (melanocytes, iridophores and xanthophores) while medaka have four (three shared with zebrafish, plus leucophores), raising questions about how conserved mechanisms of fate specification of each pigment cell type are in these fish. We have previously shown that the Sry-related transcription factor Sox10 is crucial for fate specification of pigment cells in zebrafish, and that Sox5 promotes xanthophores and represses leucophores in a shared xanthophore/leucophore progenitor in medaka. Employing TILLING, TALEN and CRISPR/Cas9 technologies, we generated medaka and zebrafish sox5 and sox10 mutants and conducted comparative analyses of their compound mutant phenotypes. We show that specification of all pigment cells, except leucophores, is dependent on Sox10. Loss of Sox5 in Sox10-defective fish partially rescued the formation of all pigment cells in zebrafish, and melanocytes and iridophores in medaka, suggesting that Sox5 represses Sox10-dependent formation of these pigment cells, similar to their interaction in mammalian melanocyte specification. In contrast, in medaka, loss of Sox10 acts cooperatively with Sox5, enhancing both xanthophore reduction and leucophore increase in sox5 mutants. Misexpression of Sox5 in the xanthophore/leucophore progenitors increased xanthophores and reduced leucophores in medaka. Thus, the mode of Sox5 function in xanthophore specification differs between medaka (promoting) and zebrafish (repressing), which is also the case in adult fish. Our findings reveal surprising diversity in even the mode of the interactions between Sox5 and Sox10 governing specification of pigment cell types in medaka and zebrafish, and suggest that this is related to the evolution of a fourth pigment cell type.

How individual cell fates become specified from multipotent progenitors is a fundamental question in developmental and stem cell biology. Body pigment cells derive from a multipotent progenitor, but while in zebrafish there are three types of pigment cells (melanocytes, iridophores and xanthophores), in medaka these progenitors form four (as zebrafish, plus leucophores). Here, we address whether mechanisms generating each cell-type are conserved between the two species. We focus on two key regulatory proteins, Sox5 and Sox10, which we previously showed were involved in pigment cell development in medaka and zebrafish, respectively. We compare experimentally how the two proteins interact in regulating development of each of the pigment cell lineages in these fish. We show that development of all pigment cells, except leucophores, is dependent on Sox10, and that Sox5 modulates Sox10 activity antagonistically in all pigment cells in zebrafish, and melanocytes and iridophores in medaka. Surprisingly, in medaka, Sox5 acts co-operatively with Sox10 to promote xanthophore fate and to repress leucophore fate. Our findings reveal surprising diversity how Sox5 and Sox10 interact to govern pigment cell development in medaka and zebrafish, and suggest that this likely relates to the evolution of the novel leucophore pigment cell type in medaka.

Comparisons of Porcine Hepatocyte Spheroids and Single Hepatocytes in the Non-Woven Fabric Bioartificial Liver Module

We previously developed a new bioreactor of the bioartificial liver composed of non-woven fabric. We have also experimented with hepatocyte spheroids, with the aim of improving the efficiency of this NWF bioreactor. In this study, we compared the efficiencies of NWF bioreactors employing hepatocyte spheroids versus single hepatocytes. Hepatocytes were isolated from a whole pig liver by Seglen's method. 1.0 × 1010 single hepatocytes were immobilized in the NWF bioreactor. Another 1.0 × 1010 hepatocytes were allowed to form spheroids by 24 hr suspension culture in a 4-L culture vessel, before being immobilized in the bioreactor. Hepatocyte spheroids were found to be functionally superior, on a per-cell basis, to single hepatocytes in the NWF bioreactor. However, the NWF bioreactor employing hepatocyte spheroids exhibited lower efficiency than that employing single hepatocytes, because the total number of the hepatocytes had decreased during the 24 hr suspension culture.

Large-Scale Preparation and Function of Porcine Hepatocyte Spheroids

To obtain a large number of porcine hepatocyte aggregates (spheroids) that have great potential in a bioartificial liver (BAL), we performed spheroid formation at a high cell density in a 1-L-scale spinner flask fitted with a silicon tubing apparatus for oxygen supply. We thereby obtained, within 24 hours, approximately fifty times more porcine hepatocyte spheroids as compared with the results of previous reports. The amount obtained corresponds to 2.5×109 cells and to roughly one-sixth of the cell number required for a BAL for a human patient. When we cultured spheroids continuously in suspension, they expressed three times more albumin secretion and twice the ammonium removal as compared with conventional monolayers during 10 days culture. Collagen gel entrapment of spheroids particularly lowered albumin secretion. We therefore conclude that the supension culture vessel of porcine hepatocyte spheroids is one of the most promising module types.

Highly efficient generation of knock-in transgenic medaka by CRISPR/Cas9-mediated genome engineering

BACKGROUND

Medaka (Oryzias latipes) is a popular animal model used in vertebrate genetic analysis. Recently, an efficient (~ 30%) knock-in system via non-homologous end joining (NHEJ) was established in zebrafish using the CRISPR/Cas9 system. If the same technique were applicable in medaka, it would greatly expand the usefulness of this model organism. The question of the applicability of CRISPR/Cas9 in medaka, however, has yet to be addressed.

RESULTS

We report the highly efficient generation of knock-in transgenic medaka via non-homologous end joining (NHEJ). Donor plasmid containing a heat-shock promoter and a reporter gene was co-injected with a short guide RNA (sgRNA) targeted for genome digestion, an sgRNA targeted for donor plasmid digestion, and Cas9 mRNA. Broad transgene expression in the expression domain of a target gene was observed in approximately 25% of injected embryos. By raising these animals, we established stable knock-in transgenic fish with several different constructs for five genetic loci, obtaining transgenic founders at efficiencies of > 50% for all five loci. Further, we show that the method is useful for obtaining mutant alleles. In the experiments where transgene integrations were targeted between the transcription start site and the initiation methionine, the resultant transgenic fish became mutant alleles.

CONCLUSION

With its simplicity, design flexibility, and high efficiency, we propose that CRISPR/Cas9-mediated knock-in via NHEJ will become a standard method for the generation of transgenic and mutant medaka.

Efficacy of Immunoadsorbent Devices for Maintaining Hepatic Function in Ex Vivo Direct Xenogenic Hemoperfusion

We have developed a new system for direct xenogenic hemoperfusion of a bioartificial liver support system adopting two types of immunoadsorbent devices. In this study, we compared the efficacy of each immunoadsorbent device in maintaining porcine hepatocyte function during 3 h perfusion treatment in a canine liver failure model. Suppression of humoral immunity by the immunoglobulin adsorber prevented immunogenic hepatocyte injury more effectively, and the system showed higher hepatic function when compared with suppression of cell-mediated immunity by the leukocyte adsorber. However, single use of immunoglobulin adsorber was less effective in reducing patients' systemic ammmonia levels and modulating the Fischer's ratio compared with the case of combined use of both immunoadsorbent devices. These results suggest that suppression of humoral immunity was of primary importance in preventing immunogenic hepatocyte injury, however the adsorption of leukocytes may have a synergic effect on maintaining hepatocyte function in direct xenogenic hemoperfusion.

Ovarian aromatase loss-of-function mutant medaka undergo ovary degeneration and partial female-to-male sex reversal after puberty

Although estrogens have been generally considered to play a critical role in ovarian differentiation in non-mammalian vertebrates, the specific functions of estrogens during ovarian differentiation remain unclear. We isolated two mutants with premature stops in the ovarian aromatase (cyp19a1) gene from an N-ethyl-N-nitrosourea-based gene-driven mutagenesis library of the medaka, Oryzias latipes. In XX mutants, gonads first differentiated into normal ovaries containing many ovarian follicles that failed to accumulate yolk. Subsequently, ovarian tissues underwent extensive degeneration, followed by the appearance of testicular tissues on the dorsal side of ovaries. In the newly formed testicular tissue, strong expression of gsdf was detected in sox9a2-positive somatic cells surrounding germline stem cells suggesting that gsdf plays an important role in testicular differentiation during estrogen-depleted female-to-male sex reversal. We conclude that endogenous estrogens synthesized after fertilization are not essential for early ovarian differentiation but are critical for the maintenance of adult ovaries.

Deficiency of Serotonin in Raphe Neurons and Altered Behavioral Responses in Tryptophan Hydroxylase 2-Knockout Medaka (Oryzias latipes)

Serotonin (5-hydroxytryptamine [5-HT]) is a bioactive monoamine that acts as a neurotransmitter in the central and peripheral nervous system of animals. Teleost fish species have serotonergic neurons in the raphe nuclei of the brainstem; however, the role of 5-HT in the raphe neurons in teleost fish remains largely unknown. Here, we established a medaka (Oryzias latipes) strain with targeted disruption of tryptophan hydroxylase 2 (tph2) gene that is involved in the 5-HT synthesis in the raphe nuclei. Immunohistochemistry and mass spectrometry analysis revealed that the homozygous mutants (tph2^Δ13/Δ13) lacked the ability to synthesize 5-HT in the raphe neurons. To investigate the effects of 5-HT deficiency in adult behaviors, the mutant fish were subjected to five behavioral paradigms (diving, open-field, light-dark transition, mirror-biting, and two-fish social interaction). The homozygous mutation caused a longer duration of freezing response in all examined paradigms and reduced the number of entries to the top area in the diving test. In addition, the mutants exhibited a decreased number of mirror-biting in the males and an increased contact time in direct social interaction between the females. These results indicate that this tph2-knockout medaka serves as a good model to analyze the effects of 5-HT deficiency in the raphe neurons.

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. Medaka are active and exhibit clear phototaxis in conditions simulating summer, but remain at the bottom of the tank and fail to exhibit phototaxis in conditions simulating winter. Mate preference tests using virtual fish created with computer graphics demonstrate that medaka are more attracted to orange-red-colored model fish in summer than in winter. Transcriptome analysis of the eye reveals dynamic seasonal changes in the expression of genes encoding photopigments and their downstream pathways. Behavioral analysis of photopigment-null fish shows significant differences from wild type, suggesting that plasticity in color perception is crucial for the emergence of seasonally regulated behaviors.

Animal coloration and behavior can change seasonally, but it is unclear if visual sensitivity to color shifts as well. Here, Shimmura et al. show that medaka undergo seasonal behavioral change accompanied by altered expression of opsin genes, resulting in reduced visual sensitivity to mates during winter-like conditions.

Short-Term Hypothermic Preservation of Porcine Hepatocyte Spheroids using uw Solution

The feasibility of University of Wisconsin (UW) solution in short-term hypothermic preservation of porcine hepatocyte spheroids was investigated, because they have great potential in bioartificial liver (BAL) systems. Porcine hepatocyte spheroids preserved for 3 days expressed almost comparable levels of albumin secretion as those without preservation, during 8 subsequent days of recultivation in continuous rotational culture, whereas isolated single cells did not reorganize into spheroids and completely lost their function in recultivation. Although for 3-day–preserved spheroids, the albumin secretion was lowered immediately after recultivation (Days 0–2), it was completely restored to that of nonpreserved ones. The function was completely lost in recultivation for 7-day–preserved ones. These results demonstrate that reorganization into spheroids is effective in preventing the functional loss of porcine hepatocytes occurring in hypothermic preservation, and that spheroid formation should precede the preservation as long as spheroid culture is finally used in BAL systems. Also, porcine hepatocyte spheroids are shown to be satisfactory stored in UW solution up to 3 days without significant cellular or functional loss.

Production of the medaka derived from vitrified whole testes by germ cell transplantation

The medaka (Oryzias latipes) is a teleost model distinguished from other model organisms by the presence of inbred strains, wild stocks, and related species. Cryopreservation guarantees preservation of these unique biological resources. However, because of their large size, cryopreservation techniques for their eggs and embryos have not been established. In the present study, we established a methodology to produce functional gametes from cryopreserved testicular cells (TCs). Whole testes taken from medaka were cryopreserved by vitrification. After thawing, the cells dissociated from cryopreserved testicular tissues were intraperitoneally transplanted into sterile triploid hatchlings. Some cells, presumably spermatogonial stem cells, migrated into the genital ridges of recipients and resulted in the production of eggs or sperm, based on sex of the recipient. Mating of recipients resulted in successful production of cryopreserved TC-derived offspring. We successfully produced individuals from the Kaga inbred line, an endangered wild population in Tokyo, and a sub-fertile mutant (wnt4b^−/−) from cryopreserved their TCs. This methodology facilitates semi-permanent preservation of various medaka strains.

Mutation in cpsf6/CFIm68 (Cleavage and Polyadenylation Specificity Factor Subunit 6) causes short 3'UTRs and disturbs gene expression in developing embryos, as revealed by an analysis of primordial germ cell migration using the medaka mutant naruto

Our previous studies analyzing medaka mutants defective in primordial germ cell (PGC) migration identified cxcr4b and cxcr7, which are both receptors of the chemokine sdf1/cxcl12, as key regulators of PGC migration. Among PGC migration mutants, naruto (nar) is unique in that the mutant phenotype includes gross morphological abnormalities of embryos, suggesting that the mutation affects a broader range of processes. A fine genetic linkage mapping and genome sequencing showed the nar gene encodes Cleavage and Polyadenylation Specificity Factor subunit 6 (CPSF6/CFIm68). CPSF6 is a component of the Cleavage Factor Im complex (CFIm) which plays a key role in pre-mRNA 3'-cleavage and polyadenylation. 3'RACE of sdf1a/b and cxcr7 transcripts in the mutant embryos indicated shorter 3'UTRs with poly A additions occurring at more upstream positions than wild-type embryos, suggesting CPSF6 functions to prevent premature 3'UTR cleavage. In addition, expression of the coding region sequences of sdf1a/b in nar mutants was more anteriorly extended in somites than wild-type embryos, accounting for the abnormally extended distribution of PGCs in nar mutants. An expected consequence of shortening 3'UTR is the escape from the degradation mechanism mediated by microRNAs interacting with distal 3'UTR sequence. The abnormal expression pattern of sdf1a coding sequence may be at least partially accounted for by this mechanism. Given the pleiotropic effects of nar mutation, further analysis using the nar mutant will reveal processes in which CPSF6 plays essential regulatory roles in poly A site selection and involvement of 3'UTRs in posttranscriptional gene regulation in various genes in vivo.

Effects of bepridil on stretch-activated BKca channels and stretch-induced extrasystoles in isolated chick hearts

Various types of mechanosensitive ion channels, including cationic stretch-activated channels (SAC(NS)) and stretch-activated BKca (SAKca) channels, modulate heart rhythm. Bepridil has been used as an antiarrhythmic drug with multiple pharmacological effects; however, whether it is effective for mechanically induced arrhythmia has not been well investigated. To test the effects of Bepridil on SAKca channels activity, cultured chick embryonic ventricular myocytes were used for single-channel recordings. Bepridil significantly reduced the open probability of the SAKca channel (P(O)). Next, to test the effects of bepridil on stretch-induced extrasystoles (SIE), we used an isolated 2-week-old Langendorff-perfused chick heart. The left ventricle (LV) volume was rapidly changed, and the probability of SIE was calculated in the presence and absence of bepridil, and the effect of the drug was compared with that of Gadolinium (Gd(3+)). Bepridil decreased the probability of SIE despite its suppressive effects on SAKca channel activity. The effects of Gd(3+), which blocks both SAKca and SAC(NS), on the probability of SIE were the same as those of bepridil. Our results suggest that bepridil blocks not only SAKca channels but possible also blocks SAC(NS), and thus decreases the stretch-induced cation influx (stabilizing membrane potential) to compensate and override the effects of the decrease in outward SAKca current (destabilizing membrane potential).

Alendronate does not prevent long bone fragility in an inactive rat model

The lack of estrogen and inactivity are both important in the pathogenesis of osteoporosis in elderly women, and there have been no appropriate rodent studies to examine the effects of common bisphosphonates on these two components separately. We compared the efficacy of alendronate (ALN) on the long bones of aged female rats, which were sedentary, estrogen deficient, or both. The rats were either forced to remain in a sitting position or allowed to walk in standard cages with or without ALN administration. The 8-week experimental period began 5 weeks after ovariectomy or sham surgery. Parameters of the hindlimb bones were determined by a three-point bending test, peripheral quantitative computed tomography, microfocus computed tomography, confocal laser Raman microspectroscopy, and dynamic histomorphometry. Regardless of ovariectomy, ALN was ineffective against the deterioration of breaking stress caused by sitting even though the trabecular bone mineral density was significantly higher in the sitting-ALN groups. Toughness was significantly deficient in the ovariectomy sitting-ALN group. This was in agreement with the bone geometry with a greater marrow space. Sitting also increased the mineral-to-matrix ratio and the carbonate-to-phosphate ratio, both indicative of aged bone. A greater loss of proteinaceous amide intensity compared with mineral intensity resulted in an increased mineral-to-matrix ratio in the presence of ALN. Sitting resulted in deficits in the quality and the geometry of cortical bone, resulting in fragility. The use of bisphosphonates, such as ALN, may provide a therapy best suited for osteoporotic individuals whose daily activity is not limited.

Mate-guarding behavior enhances male reproductive success via familiarization with mating partners in medaka fish

Background

Male-male competition and female mating preference are major mechanisms of sexual selection, which influences individual fitness. How male-male competition affects female preference, however, remains poorly understood. Under laboratory conditions, medaka (Oryzias latipes) males compete to position themselves between a rival male and the female (mate-guarding) in triadic relationships (male, male, and female). In addition, females prefer to mate with visually familiar males. In the present study, to examine whether mate-guarding affects female preference via visual familiarization, we established a novel behavioral test to simultaneously quantify visual familiarization of focal males with females and mate-guarding against rival males. In addition, we investigated the effect of familiarization on male reproductive success in triadic relationships.

Results

Three fish (female, male, male) were placed separately in a transparent three-chamber tank, which allowed the male in the center (near male) to maintain closer proximity to the female than the other male (far male). Placement of the wild-type male in the center blocked visual familiarization of the far male by the female via mate-guarding. In contrast, placement of an arginine-vasotocin receptor mutant male, which exhibits mate-guarding deficits, in the center, allowing for maintaining close proximity to the female, did not block familiarization of the far male by the female. We also demonstrated that the reproductive success of males was significantly decreased by depriving females visual familiarization with the males.

Conclusions

Our findings indicated that, at least in triadic relationships, dominance in mate-guarding, not simply close proximity, allows males to gain familiarity with the female over their rivals, which may enhance female preference for the dominant male. These findings focusing on the triadic relationships of medaka may contribute to our understanding of the adaptive significance of persistent mate-guarding, as well as female preference for familiar mates.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-016-0152-2) contains supplementary material, which is available to authorized users.

Arginine vasotocin neuronal development and its projection in the adult brain of the medaka

The neurohypophysial peptide arginine vasotocin (AVT) and its mammalian ortholog arginine vasopressin function in a wide range of physiological and behavioral events. Here, we generated a new line of transgenic medaka (Oryzias latipes), which allowed us to monitor AVT neurons by enhanced green fluorescent protein (EGFP) and demonstrate AVT neuronal development in the embryo and the projection of AVT neurons in the adult brain of avt-egfp transgenic medaka. The onset of AVT expression manifested at 2 days postfertilization (dpf) as a pair of signals in the telencephalon of the brain. The telencephalic AVT neurons migrated and converged on the preoptic area (POA) by 4dpf. At the same stage, another onset of AVT expression manifested in the central optic tectum (OT), and they migrated to the ventral part of the hypothalamus (VH) by 6dpf. In the adult brain, the AVT somata with EGFP signals existed in the gigantocellular POA (gPOA), magnocellular POA (mPOA), and parvocellular POA (pPOA) and in the VH. Whereas the major projection of AVT fibers was found from the pPOA and VH to the posterior pituitary, it was also found that AVT neurons in the three POAs send their fibers into wide regions of the brain such as the telencephalon, mesencephalon and diencephalon. This study suggests that the avt-egfp transgenic medaka is a useful model to explore AVT neuronal development and function.

Viable neuronopathic Gaucher disease model in Medaka (Oryzias latipes) displays axonal accumulation of alpha-synuclein

Homozygous mutations in the glucocerebrosidase (GBA) gene result in Gaucher disease (GD), the most common lysosomal storage disease. Recent genetic studies have revealed that GBA mutations confer a strong risk for sporadic Parkinson’s disease (PD). To investigate how GBA mutations cause PD, we generated GBA nonsense mutant (GBA-/-) medaka that are completely deficient in glucocerebrosidase (GCase) activity. In contrast to the perinatal death in humans and mice lacking GCase activity, GBA-/- medaka survived for months, enabling analysis of the pathological progression. GBA-/- medaka displayed the pathological phenotypes resembling human neuronopathic GD including infiltration of Gaucher cell-like cells into the brains, progressive neuronal loss, and microgliosis. Detailed pathological findings represented lysosomal abnormalities in neurons and alpha-synuclein (α-syn) accumulation in axonal swellings containing autophagosomes. Unexpectedly, disruption of α-syn did not improve the life span, formation of axonal swellings, neuronal loss, or neuroinflammation in GBA-/- medaka. Taken together, the present study revealed GBA-/- medaka as a novel neuronopathic GD model, the pahological mechanisms of α-syn accumulation caused by GCase deficiency, and the minimal contribution of α-syn to the pathogenesis of neuronopathic GD.

Parkinson’s disease (PD) is a neurodegenerative disease characterized by intraneuronal accumulation of alpha-synuclein (α-syn) called Lewy bodies and Lewy neurites. Recent genetic studies have revealed that mutations in glucocerebrosidase (GBA), a causative gene of Gaucher disease (GD), are a strong risk for PD. However, its pathological mechanisms leading to PD remain largely unknown. Here, we generated GBA nonsense mutant (GBA^-/-) medaka which survive long enough for pathological analysis of disease progression. These mutant medaka display not only the phenotypes resembling human neuronopathic GD but also axonal accumulation of α-syn accompanied by impairment of the autophagy-lysosome pathway. Furthermore, the present study demonstrates this α-syn accumulation has negligible contribution to the pathogenesis of neuronopathic GD in medaka. GBA^-/- medaka represent a valuable model for exploring the pathological mechanisms of PD with GBA mutations as well as neuronopathic GD, and our findings have important implications for the association of GBA mutations with PD.

An essential role of the arginine vasotocin system in mate-guarding behaviors in triadic relationships of medaka fish (Oryzias latipes)

To increase individual male fitness, males of various species remain near a (potential) mating partner and repel their rivals (mate-guarding). Mate-guarding is assumed to be mediated by two different types of motivation: sexual motivation toward the opposite sex and competitive motivation toward the same sex. The genetic/molecular mechanisms underlying how mate presence affects male competitive motivation in a triadic relationship has remained largely unknown. Here we showed that male medaka fish prominently exhibit mate-guarding behavior. The presence of a female robustly triggers male-male competition for the female in a triadic relationship (2 males and 1 female). The male-male competition resulted in one male occupying a dominant position near the female while interfering with the other male's approach of the female. Paternity testing revealed that the dominant male had a significantly higher mating success rate than the other male in a triadic relationship. We next generated medaka mutants of arginine-vasotocin (avt) and its receptors (V1a1, V1a2) and revealed that two genes, avt and V1a2, are required for normal mate-guarding behavior. In addition, behavioral analysis of courtship behaviors in a dyadic relationship and aggressive behaviors within a male group revealed that avt mutant males displayed decreased sexual motivation but showed normal aggression. In contrast, heterozygote V1a2 mutant males displayed decreased aggression, but normal mate-guarding and courtship behavior. Thus, impaired mate-guarding in avt and V1a2 homozygote mutants may be due to the loss of sexual motivation toward the opposite sex, and not to the loss of competitive motivation toward rival males. The different behavioral phenotypes between avt, V1a2 heterozygote, and V1a2 homozygote mutants suggest that there are redundant systems to activate V1a2 and that endogenous ligands activating the receptor may differ according to the social context.

Gene replacement by zinc finger nucleases in medaka embryos

Gene replacement (GR) via homologous recombination is a powerful tool for genome editing. Recently, direct GR is achieved successfully by coinjection of mRNAs for engineered endonucleases such as zinc finger nucleases (ZFNs) and donor DNA in developing embryos of diverse organisms. Here, we report the procedures and efficiency for direct GR by using ZFNs in the fish medaka. Upon zygotic coinjection of mRNAs encoding ZFNs that target the gonad-specifically expressed gsdf locus, linear DNA of GR vector pGRgsdf containing the red fluorescent protein (rfp) gene flanked by two homology arms of ~1-kb each underwent GR via homologous recombination. Specifically, 15 of 231 adults from manipulated embryos contained a GR allele in the caudal fin, producing an efficiency of ~7 % for somatic GR. Progeny test revealed that two out of nine fertile fish containing the GR allele in the fin were capable of transmitting the GR allele to ~6 % of F1 generation at adulthood, generating an efficiency of ~22 % for germline transmission. Sequencing and Southern blotting validated precise GR. We show that the GR allele expressed a chimeric gsdf:rfp RNA between gsdf and cointegrated rfp specifically in the gonad, demonstrating recapitulation of endogenous RNA expression as predicted for the defined GR allele. Most importantly, RFP expression coincides faithfully with the gonad-specific gsdf expression in developing embryos and adults. These results demonstrate, for the first time, the feasibility and efficiency of ZFN-mediated precise GR directly in the developing embryo of medaka as a lower vertebrate model.

Genetic control of startle behavior in medaka fish

Genetic polymorphisms are thought to generate intraspecific behavioral diversities, both within and among populations. The mechanisms underlying genetic control of behavioral properties, however, remain unclear in wild-type vertebrates, including humans. To explore this issue, we used diverse inbred strains of medaka fish (Oryzias latipes) established from the same and different local populations. Medaka exhibit a startle response to a visual stimulus (extinction of illumination) by rapidly bending their bodies (C-start) 20-ms after the stimulus presentation. We measured the rates of the response to repeated stimuli (1-s interval, 40 times) among four inbred strains, HNI-I, HNI-II, HO5, and Hd-rR-II1, and quantified two properties of the startle response: sensitivity (response rate to the first stimulus) and attenuation of the response probability with repeated stimulus presentation. Among the four strains, the greatest differences in these properties were detected between HNI-II and Hd-rR-II1. HNI-II exhibited high sensitivity (approximately 80%) and no attenuation, while Hd-rR-II1 exhibited low sensitivity (approximately 50%) and almost complete attenuation after only five stimulus presentations. Our findings suggested behavioral diversity of the startle response within a local population as well as among different populations. Linkage analysis with F2 progeny between HNI-II and Hd-rR-II1 detected quantitative trait loci (QTL) highly related to attenuation, but not to sensitivity, with a maximum logarithm of odds score of 11.82 on linkage group 16. The three genotypes (homozygous for HNI-II and Hd-rR-II1 alleles, and heterozygous) at the marker nearest the QTL correlated with attenuation. Our findings are the first to suggest that a single genomic region might be sufficient to generate individual differences in startle behavior between wild-type strains. Further identification of genetic polymorphisms that define the behavioral trait will contribute to our understanding of the neural mechanisms underlying behavioral diversity, allowing us to investigate the adaptive significance of intraspecific behavioral polymorphisms of the startle response.