Establishment of a Simplified System to Evaluate Salinity Preference and Validation of Behavioral Salinity Selection in the Japanese Medaka, Oryzias latipes

In fishes, it is necessary to select a salinity environment suitable for survival. However, little is known about the mechanisms regarding detection and selection of salinity environments in fish. This study involved the establishment of a simple aquarium system in which fish can swim between freshwater (FW) and seawater (SW) in a single tank. In this tank, the lower level contained SW, the upper level contained FW, and the FW and SW levels were clearly separated as different salinity areas. Behavioral experiments of salinity environment selection using this simplified system to evaluate salinity preference showed that FW-acclimated medakas preferred FW to SW. In contrast, SW-acclimated medakas preferred SW to FW. These results indicate that euryhaline medakas prefer the saline habitats to which they are acclimated, when able to select the salinity environment. We identified the taste receptor type-2 and polycystic kidney disease 2-like 1 genes as possibly related to high-salinity taste in medaka. The expression of these genes increased at certain time points after SW challenges. In this study, we established an aquarium system to facilitate a simple experiment for salinity preference. Our results suggest that the medaka is good model for research related to seawater environment selection in fish

A defective interleukin-17 receptor A1 causes weight loss and intestinal metabolism-related gene downregulation in Japanese medaka, Oryzias latipes

Abstract In the intestine, the host must be able to control the gut microbiota and efficiently absorb transiently supplied metabolites, at the risk of enormous infection. In mammals, the inflammatory cytokine interleukin (IL)-17A/F is one of the key mediators in the intestinal immune system. However, many functions of IL-17 in vertebrate intestines remain unclarified. In this study, we established a gene-knockout (KO) model of IL-17 receptor A1 (IL-17RA1, an IL-17A/F receptor) in Japanese medaka (Oryzias latipes) using genome editing technique, and the phenotypes were compared to wild type (WT) based on transcriptome analyses. Upon hatching, homozygous IL-17RA1-KO medaka mutants showed no significant morphological abnormality. However, after 4 months, significant weight decreases and reduced survival rates were observed in IL-17RA1-KO medaka. Comparison of gene-expression patterns in WT and IL-17RA1-KO medaka revealed that various metabolism- and immune-related genes were significantly down-regulated in IL-17RA1-KO medaka intestine, particularly genes related to mevalonate metabolism (mvda, acat2, hmgcs1, and hmgcra) and genes related to IL-17 signaling (such as il17c, il17a/f1, and rorc) were found to be decreased. Conversely, expression of genes related to cardiovascular system development, including fli1a, sox7, and notch1b in the anterior intestine, and that of genes related to oxidation–reduction processes including ugp2a, aoc1, and nos1 in posterior intestine was up-regulated in IL-17RA1-KO medaka. These findings show that IL-17RA regulated immune- and various metabolism-related genes in the intestine for maintaining the health of Japanese medaka

Additional file 2: Figure S1. of Past seawater experience enhances seawater adaptability in medaka, Oryzias latipes

Changes in gene expressions of Na+/K+-ATPase α-subunits 1a (A), α1c (B), α2 (C) and α3a (D) after direct SW transfer of SW-experienced medaka (solid circles) and control FW medaka (open circles). Values are means ± SEM. Numerals in parentheses indicate the number of samples examined. Different letters indicate significant differences within the same group (ANOVA, Tukey-Kramer multiple comparison test, p < 0.05). Asterisks indicate significant differences between the two groups at the same time points (two-sided Student’s t test, *p < 0.05 and **p < 0.01). (TIF 5121 kb

Additional file 1: Table S1. of Past seawater experience enhances seawater adaptability in medaka, Oryzias latipes

Primers used for cloning and real-time qPCR analyses. (XLSX 11 kb

Establishment and validation of an aquarium system to evaluate salinity preference in conscious rainbow trout

Anadromous salmon migrate between fresh water (FW) and seawater (SW) during their life cycle, which most likely is driven by changes in salinity preference. There have been some studies examining salinity preference in juveniles during downstream migration, but no study has yet been reported in homing adults. In this study, we established an aquarium system to evaluate salinity preference that is usable not only for juveniles but for adult fish. The aquarium consists of three areas of different salinities, a FW area, a SW area and a brackish water (BW) area, among which fish can voluntarily move. By modifying the flow rate of FW/SW and other parameters, we could maintain the salinity of the FW area at 20 ppt irrespective of the depth, but the salinity varies considerably by depth between the surface and bottom layer in the BW area. Two aquaria with the same system were prepared side by side, an acclimation aquarium that allowed fish to learn the system before the experiment and an experimental aquarium that was insulated from the environment and observed by a video system. Using this aquarium system, we found that cultured rainbow trout, Oncorhynchus mykiss, of ca. 200g preferred areas in the order of BW≥FW>>SW. To further validate this system, we injected various hormones that have been implicated in osmoregulation/smoltification such as angiotensin II (Ang II), cortisol, thyroid hormone (T3), arginine vasotocin (AVT) and prolactin into the third brain ventricle of the trout and observed their preference behavior. There was a tendency toward high salinity preference after injection of hormones that promote SW acclimation and/or smoltification (Ang II, cortisol T3 and AVT), but fish tended to prefer a low salinity area after injection of prolactin that promotes FW adaptation. These results suggest that the newly established aquarium system can be used to evaluate salinity preference in salmonids and will contribute to future studies in identidying key factors that motivate downstream migration of juveniles and upstream migration of mature chum salmon, O. keta, homing to natal rivers in the Tohoku area of Japan

Establishment and validation of an aquarium system to evaluate salinity preference in conscious rainbow trout

Anadromous salmon migrate between fresh water (FW) and seawater (SW) during their life cycle, which most likely is driven by changes in salinity preference. There have been some studies examining salinity preference in juveniles during downstream migration, but no study has yet been reported in homing adults. In this study, we established an aquarium system to evaluate salinity preference that is usable not only for juveniles but for adult fish. The aquarium consists of three areas of different salinities, a FW area, a SW area and a brackish water (BW) area, among which fish can voluntarily move. By modifying the flow rate of FW/SW and other parameters, we could maintain the salinity of the FW area at <0.5 ppt (part per thousand) and that of the SW area at >20 ppt irrespective of the depth, but the salinity varies considerably by depth between the surface and bottom layer in the BW area. Two aquaria with the same system were prepared side by side, an acclimation aquarium that allowed fish to learn the system before the experiment and an experimental aquarium that was insulated from the environment and observed by a video system. Using this aquarium system, we found that cultured rainbow trout, Oncorhynchus mykiss, of ca. 200g preferred areas in the order of BW≥FW>>SW. To further validate this system, we injected various hormones that have been implicated in osmoregulation/smoltification such as angiotensin II (Ang II), cortisol, thyroid hormone (T3), arginine vasotocin (AVT) and prolactin into the third brain ventricle of the trout and observed their preference behavior. There was a tendency toward high salinity preference after injection of hormones that promote SW acclimation and/or smoltification (Ang II, cortisol T3 and AVT), but fish tended to prefer a low salinity area after injection of prolactin that promotes FW adaptation. These results suggest that the newly established aquarium system can be used to evaluate salinity preference in salmonids and will contribute to future studies in identidying key factors that motivate downstream migration of juveniles and upstream migration of mature chum salmon, O. keta, homing to natal rivers in the Tohoku area of Japan

miR-7977 inhibits the Hippo-YAP signaling pathway in bone marrow mesenchymal stromal cells.

We and others have demonstrated that various abnormalities of the bone marrow (BM) mesenchymal stromal cells (MSCs) such as aberrant cytokine expression, abnormal hedgehog signaling, and impaired miRNA biogenesis are observed in patients with acute myeloid leukemia (AML). However, underlying mechanisms to induce the dysfunction of BM MSCs have not yet been clarified. We previously showed that AML cells release abundant exosomal miR-7977, which, in turn, enters BM mesenchymal stromal cells (MSCs). However, the precise function of miR-7977 is not known. In this study, we performed transduction of a miR-7977 mimic into MSCs, compared transcriptomes between control-transduced (n = 3) and miR-7977-transduced MSCs (n = 3), and conducted pathway analysis. The array data revealed that the expression of 0.05% of genes was reduced 2-fold and the expression of 0.01% of genes was increased 2-fold. Interestingly, approximately half of these genes possessed a miR-7977 target site, while the other genes did not, suggesting that miR-7977 regulates the gene expression level directly and indirectly. Gene set enrichment analysis showed that the gene sets of Yes-associated protein 1 (YAP1) _up were significantly enriched (p<0.001, q<0.25), suggesting that miR-7977 modulates the Hippo-YAP signaling pathway. Visualization of pathway and network showed that miR-7977 significantly reduced the expression of Hippo core kinase, STK4. miR-7977 inactivated the Hippo-YAP signaling pathway as proven by GFP-tagged YAP nuclear trans localization and TEAD reporter assay. The miR-7977-transduced MSC cell line, HTS-5, showed elevated saturation density and enhanced entry into the cell cycle. These results suggest that miR-7977 is a critical factor that regulates the Hippo-YAP signaling pathway in BM-MSCs and may be involved in the upregulation of leukemia-supporting stroma growth