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The tiger puffer Takifugu rubripes is one of the most popular aquacultural fish; however, there are two major obstacles to selective breeding. First, they have a long generation time of 2 or 3 years until maturation. Second, the parental tiger puffer has a body size (2–5 kg) much larger than average market size (0.6–1.0 kg). The grass puffer Takifugu niphobles is closely related to the tiger puffer and matures in half the time. Furthermore, grass puffer can be reared in small areas since their maturation weight is about 1/150 that of mature tiger puffer. Therefore, to overcome the obstacles of maturation size and generation time of tiger puffer, we generated surrogate grass puffer that can produce tiger puffer gametes through germ cell transplantation. Approximately 5000 tiger puffer testicular cells were transplanted into the peritoneal cavity of triploid grass puffer larvae at 1 day post hatching. When the recipient fish matured, both males and females produced donor-derived gametes. Through their insemination, we successfully produced donor-derived tiger puffer offspring presenting the same body surface dot pattern, number of dorsal fin rays, and DNA fingerprint as those of the donor tiger puffer, suggesting that the recipient grass puffer produced functional eggs and sperm derived from the donor tiger puffer. Although fine tunings are still needed to improve efficiencies, surrogate grass puffer are expected to accelerate the breeding process of tiger puffer because of their short generation time and small body size.

The novel non-targeted PCR-based genotyping system, namely Genotyping by Random Amplicon Sequencing, Direct (GRAS-Di), is characterized by the simplicity in library construction and robustness against DNA degradation and is expected to facilitate advancements in genetics, in both basic and applied sciences. In this study, we tested the utility of GRAS-Di for genetic analysis in a cultured population of the tiger pufferfish Takifugu rubripes. The genetic analyses included family structure analysis, genetic map construction, and quantitative trait locus (QTL) analysis for the male precocious phenotype using a population consisting of four full-sib families derived from a genetically precocious line. An average of 4.7 million raw reads were obtained from 198 fish. Trimmed reads were mapped onto a Fugu reference genome for genotyping, and 21,938 putative single-nucleotide polymorphisms (SNPs) were obtained. These 22 K SNPs accurately resolved the sibship and parent–offspring pairs. A fine-scale linkage map (total size: 1,949 cM; average interval: 1.75 cM) was constructed from 1,423 effective SNPs, for which the allele inheritance patterns were known. QTL analysis detected a significant locus for testes weight on Chr_14 and three suggestive loci on Chr_1, Chr_8, and Chr_19. The significant QTL was shared by body length and body weight. The effect of each QTL was small (phenotypic variation explained, PVE: 3.1–5.9%), suggesting that the precociousness seen in the cultured pufferfish is polygenic. Taken together, these results indicate that GRAS-Di is a practical genotyping tool for aquaculture species and applicable for molecular breeding programs, such as marker-assisted selection and genomic selection.

Testes of the tiger pufferfish Takifugu rubripes are a delicacy in Japan, and selective breeding for a male precocious phenotype, i.e., with early initiation of testes development, is desirable. However, it is unknown if precocious gonad development in this species is under genetic control. Here, we investigated genetic involvement in precociousness by using progeny tests with sires from two cultured populations, including a family line anecdotally known for its precociousness, and a wild population. Progeny derived from the “precocious” line consistently had greater testes weight than that from the other lines, even after accounting for effects of body weight, which indicates that precociousness is truly heritable. We also compared chronological changes in plasma steroid hormones between progenies sired by males from the precocious line and a wild population, and found that the precocious family line had higher levels of plasma estradiol-17β (E2) prior to the initiation of testicular development. Our findings suggest that selective breeding for testes precociousness in the tiger pufferfish is feasible, and that plasma E2 may be an indicator of this phenotype, which would allow for phenotype evaluation without the need to sacrifice specimens.

Tuna (genus Thunnus), particularly Pacific bluefin tuna (T. orientalis; PBT), are commercially important fish in the aquaculture industry worldwide. The objective of this study was to investigate sexual dimorphism in the growth performance of aquaculture-produced PBT and develop techniques for its sex manipulation, for the first time in tuna. A comparison of the body size between sexes revealed that male-cultured PBTs were larger than females at harvest. We also confirmed that cyp19a1a (encoding a gonadal aromatase) expression increased specifically in the genotypic female PBT gonads during sex differentiation. This suggested that aromatase plays an important role in ovarian differentiation and that the suppression of aromatase activity may effectively induce masculinization in genotypic females. Therefore, we administered letrozole—an aromatase inhibitor (AI)—into sexually undifferentiated PBT through the oral route. AI administration resulted in a 100% sex reversal of genotypic females into phenotypic males at the molecular level. Our results provide the basis for future studies on the establishment of mono-sex male production technology in PBT, which would help improve the productivity of closed-cycle PBT aquaculture. Furthermore, this study offers important insights into the understanding of the sex-wise growth of tuna species in aquacultural settings, and developing sex manipulation techniques.

Tiger puffer Takifugu rubripes is one of the most valuable fish species in Japan; however, there has not been much progress in their selective breeding until recently despite their potential in aquaculture. Their long generation time and the large body size of their broodstock make breeding difficult. Recently, we made a surrogate broodstock, which produced gametes of different species in salmonids. Therefore, by using closely related recipients, which have small body sizes and short generation times, it is possible to accelerate breeding of the tiger puffer. Thus, we considered the grass puffer Takifugu niphobles, which has a short generation time and a small maturation size, as a potential recipient for gamete production of the tiger puffer. Furthermore, if sterile triploid individuals are used as recipients, the resulting surrogate broodstock would produce only donor-derived gametes. Therefore, we examined conditions for inducing triploidy by suppressing meiosis II to retain the second polar body in grass puffer. We found that cold shock treatment, which is 5°C for 30 min starting from 5 min after fertilization, is optimal to obtain high triploidization and hatching rates. Although the resulting triploid grass puffers produced small amounts of gametes in both sexes, the offspring derived from the gametes could not live for over 3 days. Furthermore, we found that triploid grass puffer showed normal plasma sex steroid levels compared with diploids. These are important characteristics of triploid grass puffer as surrogate recipients used for germ cell transplantation.

A correction to this paper has been published: https://doi.org/10.1007/s12562-021-01505-w

Acute kidney disease (AKD), or renal dysfunction persisting >7 days after an initiating event of acute kidney injury, is a rising concern. This study aimed to elucidate the clinical course of AKD after cardiac surgery with data on post-cardiac surgery patients admitted to intensive care units (ICU) at 18 Japanese hospitals during 2012–2014. Using multivariable logistic models, we evaluated the association of AKD with 90-day mortality and the 50% eGFR decline during 2-year follow-up compared to eGFR at 90 days. AKD was defined as an elevation in serum creatinine to at least 1.5-fold from baseline in >7 days after ICU admission. Of the 3,605 eligible patients undergoing cardiac surgery, 403 patients (11.2%) had AKD. Multivariable analysis revealed that the adjusted odds ratio (OR) of AKD for 90-day mortality was 63.0 (95% confidence interval [CI], 27.9–180.6). In addition, the adjusted OR of AKD for 50% eGFR decline was 3.56 (95% CI, 2.24–5.57) among hospital survivors. In conclusion, AKD after cardiac surgery was associated with higher 90-day mortality and renal function decline after hospital discharge.

Acute kidney injury (AKI) complicated by acute lung injury has a detrimental effect on mortality among critically ill patients. Recently, a renal ischemia-reperfusion (IR) model suggested the involvement of histones and neutrophil extracellular traps (NETs) in the development of distant lung injury after renal IR. Given that recombinant thrombomodulin (rTM) has anti-inflammatory roles by binding to circulating histones, we aimed to clarify its effect on distant lung injury induced by AKI in a murine bilateral renal IR model. Both pretreatment and delayed treatment with rTM significantly decreased pulmonary myeloperoxidase activity, but they did not affect renal dysfunction at 24 h after renal IR. Additionally, rTM mitigated the renal IR-augmented expression of proinflammatory cytokines (tumor necrosis factor-α, interleukin-6, and keratinocyte-derived chemokine), and vascular leakage, as well as the degree of lung damage. Intense histone accumulation and active NET formation occurred in both the kidneys and the lungs; however, rTM significantly decreased the histone and NET accumulation only in the lungs. Administration of rTM may have protective impact on the lungs after renal IR by blocking histone and NET accumulation in the lungs, although no protection was observed in the kidneys. Treatment with rTM may be an adjuvant strategy to attenuate distant lung injury complicating AKI.

For peritonitis, a serious complication of peritoneal dialysis (PD), we investigated the relation between duration from the sign (PD effluent abnormalities) to treatment with appropriate antibiotics (ST time) and catheter removal. For 62 PD hospital patients, data of PD-related peritonitis ( n  = 109) were collected retrospectively. We examined ST time and PD catheter removal times using univariate and multivariate analyses. The catheter removal rate in the delayed ST time group (≥ 24 h) was higher than that in early ST time group (< 24 h) (38 vs. 16%, p  = 0.02). Concomitant tunnel infection and delayed ST time were associated with catheter removal (OR [95% CI] 32.3 [3.15–329] and 3.52 [1.11–11.1]). Rates of catheter removal and re-development of peritonitis within 1 month after starting treatment were higher in the delayed ST time group ( p  = 0.02). PD duration at peritonitis and the first peritonitis episode were associated with delayed ST time (1.02 [1.00–1.04] and 3.42 [1.09–10.7]). Significant association was found between PD catheter removal and the start of treatment more than 24 h after appearance of abnormal effluent. Education for patients about prompt visitation at the onset of peritonitis with long PD duration might improve outcomes.

The renal angina index has been proposed to identify patients at high risk of persistent AKI, based on slight changes in serum creatinine and patient conditions. However, a concise scoring method has only been proposed for pediatric patients, and not for adult patients yet. Here, we developed and validated a concise scoring method using data on patients admitted to ICUs in 21 Japanese hospitals from 2012 to 2014. We randomly assigned to either discovery or validation cohorts, identified the factors significantly associated with persistent AKI using a multivariable logistic regression model in the discovery cohort to establish a scoring system, and assessed the validity of the scoring in the validation cohort using receiver operating characteristic analysis and the calibration slope. Among 8,320 patients admitted to the ICUs, persistent AKI was present in 1,064 (12.8%) patients. In the discovery cohort (n = 4,151), ‘hyperbilirubinemia’, ‘sepsis’ and ‘ventilator and/or vasoactive’ with small changes in serum creatinine were selected to establish the scoring. In the validation cohort (n = 4,169), the predicting model based on this scoring had a c-statistic of 0.79 (95%CI, 0.77–0.81) and was well calibrated. In conclusion, we established a concise scoring method to identify potential patients with persistent AKI, which performed well in the validation cohort.