Kenji Toyota

Kenji Toyota
Kanagawa University

Doctor of Philosophy

About

47
Publications
6,461
Reads
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806
Citations
Citations since 2017
27 Research Items
652 Citations
2017201820192020202120222023020406080100120140
2017201820192020202120222023020406080100120140
2017201820192020202120222023020406080100120140
2017201820192020202120222023020406080100120140
Additional affiliations
April 2015 - February 2016
National Institute for Basic Biology
Position
  • PostDoc Position

Publications

Publications (47)
Preprint
Full-text available
This study is the first to demonstrate that deep ocean water (DOW) has physiological significant effects on squid. After 36 h of rearing squids, those reared with DOW had significantly higher total and free cholesterol levels and lower alanine transaminase activity in hemolymph as compared with those reared with surface water (SSW). SSW rearing als...
Article
Crustaceans are a valuable food source and commercially important. In order to ensure population stability, environmental diversity and food security, understanding the underlying endocrinology of these arthropods is key. Dr Kenji Toyota, Marine Biological Station, Sado Island Center for Ecological Sustainability, Niigata University, is working on...
Chapter
Full-text available
In insects, metamorphosis is one of the most important research topics. Their drastic morphological and physiological changes from larvae to pupae, and then to adults, have fascinated many people. These changing life history patterns are tightly regulated by two endocrine systems, the ecdysteroids (molting hormones) and the juvenile hormones. Metam...
Article
To clarify the calcification mechanism of the exoskeleton of marine crustaceans, kuruma prawns (Marsupenaeus japonicus), which are commercially important prawns in Japan, were used, and calcification-associated peptide (CAP), a matrix peptide that was previously reported in red swamp crayfish, was examined. Based on the RNA-sequencing data of kurum...
Article
The water flea, Daphnia magna, is a representative zooplankton that lives in freshwater environments. It primarily propagates via asexual reproduction in normal and healthy environmental conditions. Unsuitable environmental conditions induce D. magna to change its mode of reproduction from asexual to sexual reproduction. During sexual reproduction,...
Article
Insulin-like androgenic gland factor (IAG) from the marbled crayfish Procambarus virginalis is an insulin-like heterodimeric peptide composed of A and B chains and has an Asn-linked glycan at the B chain. IAG is considered to be a male sex hormone inducing the sex differentiation to male in decapod crustacean, although there is no report on the fun...
Article
Organisms have the ability to adapt their behavior and physiology in response to seasonal changes in their habitat's environments. Although it is known that a specific light wavelength affects growth and reproduction in various animal taxa, its effect on sexual and seasonal differences in year-round breeding animals remains unclear. Here, we demons...
Article
Juvenile hormone (JH) are a family of multifunctional hormones regulating larval development, molting, metamorphosis, reproduction, and phenotypic plasticity in arthropods. Based on its importance in arthropod life histories, many insect growth regulators (IGRs) mimicking JH have been designed to control harmful insects in agriculture and aquacultu...
Article
The greasyback shrimp Metapenaeus ensis is widely distributed along the coast of India and the West Pacific where it is an important fisheries species. We have examined seasonal changes in ovarian development, spermatogenesis, and mating of Me. ensis in histological studies and by external observations on specimens collected in Ise Bay, its norther...
Article
Full-text available
Mechanisms underlying sex determination and differentiation in animals are known to encompass a diverse array of molecular clues. Recent innovations in high-throughput sequencing and mass spectrometry technologies have been widely applied in non-model organisms without reference genomes. Crustaceans are no exception. They are particularly diverse a...
Preprint
Full-text available
The water flea Daphnia magna is a representative example of zooplankton living in freshwater environments. They primarily propagate via asexual reproduction under normal and healthy environmental conditions. Environmental stimuli that signal a shift to disadvantageous conditions induce D. magna to change their mode of reproduction from asexual to s...
Article
The G protein‐coupled estrogen receptor 1 (Gper1) is a membrane‐bound estrogen receptor that mediates non‐genomic action of estrogens. A Gper1‐mediating pathway has been implicated in reproductive activities in fish, including oocyte growth, but Gper1 has been characterized in only a very limited number of fish species. In this study, we cloned and...
Article
Juvenile hormone (JH) is an important endocrine factor regulating many biological activities in arthropods. In daphnids, methoprene-tolerant (Met) belongs to a basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) family protein which has recently been confirmed as a JH receptor and can bind and be activated by JHs and JH agonists. Although the activation...
Article
Estrogens play critical roles in ovarian and reproductive organ development, but the molecular signaling pathways in non-mammalian vertebrates are not well understood. Studies of reptiles have indicated that administration of exogenous estrogens during embryonic development causes ovarian differentiation and presumptive male to female sex-reversal....
Article
Full-text available
Physiological functions of juvenile hormone (JH) and molting hormone have been demonstrated in insects. JH, molting hormone and their mimics (insect growth regulators, IGRs) show endocrine-disrupting effects not only on target pest insects but also on other arthropod species such as crustaceans. However, little is known about the endocrine-disrupti...
Article
Freshwater zooplankton Daphnia magna has been widely used in ecotoxicology studies. During the last 20 years, it has been demonstrated that the topical application of juvenile hormone (JH) or JH analogs to mother daphnids induce male offspring production. Based on this finding, an in vivo screening validation method for chemicals with JH agonistic...
Presentation
Molting is key to growth, development and reproduction in arthropods, and is precisely regulated by ecdysteroids through activation of the ecdysone receptor (EcR). Endocrine disrupting chemicals (EDCs) mimicking the actions of ecdysteroids have therefore been developed as pesticides to combat harmul arthropods. These chemicals, however, may also af...
Article
Full-text available
Temperature and photoperiod regulate key fitness traits in plants and animals. However, with temperature increase due to global warming, temperature cue thresholds are experienced at shorter photoperiods, disrupting the optimal seasonal timing of physiological, developmental and reproductive events in many species. Understanding the mechanisms of a...
Chapter
The cladoceran crustacean genus Daphnia (daphnids) exhibits a unique reproductive strategy in response to changes in environmental conditions of their habitat. This is known as environmental sex determination (ESD). Under favorable environmental conditions, daphnids produce clonal female offspring by parthenogenesis. Under unfavorable environmental...
Article
Sex steroid hormones including estrogens and androgens play fundamental roles in regulating reproductive activities and they act through estrogen and androgen receptors (ESR and AR). These steroid receptors have evolved from a common ancestor in association with several gene duplications. In most vertebrates, this has resulted in two ESR subtypes (...
Article
Photoperiodism is a biological seasonal timing system utilized to regulate development and reproduction in organisms. The freshwater micro-crustacean Daphnia pulex displays environmental sex determination, the precise physiological mechanisms of which are largely unknown due to the lack of an experimental system to induce female or male offspring p...
Article
Molting is critical for growth, development, reproduction and survival in arthropods. Complex neuroendocrine pathways are involved in the regulation of molting and may potentially become targets of environmental endocrine disrupting chemicals (EDCs). Based on several known ED mechanisms, a wide range of pesticides has been developed to combat unwan...
Article
Full-text available
Sex determination of Daphnia pulex is decided by environmental conditions. We established a suitable experimental system for this study using D. pulex WTN6 strain, in which the sex of the offspring can be controlled by photoperiod. Long-day conditions induced females and short-day conditions induced males. Using this system, we previously found tha...
Article
The freshwater zooplankton Daphnia magna has been extensively employed in chemical toxicity tests such as OECD Test Guidelines 202 and 211. Previously, it has been demonstrated that the treatment of juvenile hormones (JHs) or their analogues to female daphnids can induce male offspring production. Based on this finding, a rapid screening method for...
Article
Under favorable conditions, the micro-crustacean Daphnia pulex produces female offspring by parthenogenesis, whereas under unfavorable conditions, they produce male offspring to induce sexual reproduction (environmental sex determination: ESD). We recently established a suitable system for ESD studies using D. pulex WTN6 strain, in which the sex of...
Article
In 2010, approximately 2.1 million gallons of chemical dispersants, mainly Corexit 9500, were applied in the Gulf of Mexico to prevent the oil slick from reaching shorelines and to accelerate biodegradation of oil during the Deepwater Horizon oil spill. Recent studies have revealed toxic effects of Corexit 9500 on marine microzooplankton that play...
Chapter
It is well known that most daphnid species have several attractive life history characteris‐ tics such as cyclical parthenogenesis, environmental sex determination, and predator-in‐ duced defense formation. Recent advances in high-throughput omics technologies make it easy to obtain a huge number of potential candidate factors involved in environme...
Article
Full-text available
Embryo development in arthropods is accompanied by a series of moltings. A cladoceran crustacean Daphnia magna molts three times before reaching first instar neonate during embryogenesis. Previous studies argued ecdysteroids might regulate D. magna embryogenesis. However, no direct evidence between innate ecdysteroids fluctuation and functions has...
Article
'Saijo' Japanese persimmon ( Diospyros kaki Thumb.) is one of the most popular and commercially important fruit cultivars in Japan. In 2000, origin-unknown 'Saijo'-like cultivar was found at the Shimane farm and named as 'M-3'. Although it has similar morphological and physiological characteristics with 'Saijo' cultivars, its fruit size is apparent...
Article
The freshwater crustacean genus Daphnia has been used extensively in ecological, developmental and ecotoxicological studies. Daphnids produce only female offspring by parthenogenesis under favorable conditions, but in response to various unfavorable conditions and external stimuli, they produce male offspring. Although we reported that exogenous ex...
Article
Full-text available
The cladoceran crustacean Daphnia pulex produces female offspring by parthenogenesis under favorable conditions, but in response to various unfavorable external stimuli, it produces male offspring (environmental sex determination: ESD). We recently established an innovative system for ESD studies using D. pulex WTN6 strain, in which the sex of the...
Article
Full-text available
Background The cosmopolitan microcrustacean Daphnia pulex provides a model system for both human health research and monitoring ecosystem integrity. It is the first crustacean to have its complete genome sequenced, an unprecedented ca. 36% of which has no known homologs with any other species. Moreover, D. pulex is ideally suited for experimental m...
Article
Full-text available
Daphnia magna exhibits a parthenogenetic reproductive cycle linked to a moulting cycle, but regulatory mechanisms of neither moulting nor reproductive cycle are understood in daphnids. Moulting is regulated by ecdysteroids in insects. A previous study showed that a titre of ecdysteroids changed during the reproductive cycle in D. magna; however, no...
Article
Daphnia magna has been used extensively to evaluate organism- and population-level responses to pollutants in acute toxicity and reproductive toxicity tests. We have previously reported that exposure to juvenile hormone (JH) agonists results in a reduction of reproductive function and production of male offspring in a cyclic parthenogenesis, D. mag...
Chapter
It is well known that most daphnid species normally reproduce by parthenogenesis. However,under unfavorable conditions, such as crowding or seasonal change, male offspring are alsoproduced parthenogenetically, and then sexual reproduction occurs. Although they adoptparthenogenesis and sexual reproduction differentially in response to various enviro...
Article
Full-text available
The ubiquitous, freshwater microcrustacean Daphnia pulex provides a model system for both human health research and monitoring ecosystem integrity. It is the first crustacean to have a well annotated, reference genome assembly that revealed an unusually high gene count highlighted by a large gene orphanage,-i.e., previously uncharacterized genes. D...
Article
Juvenile hormone is an essential regulator of major developmental and life history events in arthropods. Most of the insects use juvenile hormone III as the innate juvenile hormone ligand. By contrast, crustaceans use methyl farnesoate. Despite this difference that is tied to their deep evolutionary divergence, the process of this ligand transition...
Article
Full-text available
The gene doublesex (dsx) is known as a key factor regulating genetic sex determination in many organisms. We previously identified two dsx genes (DapmaDsx1 and DapmaDsx2) from a freshwater branchiopod crustacean, Daphnia magna, which are expressed in males but not in females. D. magna produces males by parthenogenesis in response to environmental c...

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