Taisen Iguchi

Constitutive stimulation of estrogen signaling in mice causes dilated uterine glands with activation of epithelial cell proliferation. In estrogen receptor β knockout (Esr2 KO) mice, cell proliferation in the uterine epithelium is permanently stimulated; therefore, we histologically analyzed the uterine structure in Esr2 KO mice with age. In the uterus of Esr2 KO mice, dilation of the uterine glands was accelerated and the collagen was accumulated in the stroma. The uterine glands were dilated with age even in wild-type (WT) mice; however, Esr2 KO accelerated the dilation of uterine glands quantitatively. The expression of FOXA2 transcription factor, which is essential for uterine glandular function, was diminished in dilated uterine glands of WT and Esr2 KO mice and decreased in the uterine glands of normal size in 12-month-old Esr2 KO mice. To investigate mechanisms of the collagen accumulation in the Esr2 KO uterus, we focused on collagen synthesis and degradation. In the uterine stroma of Esr2 KO mice, MMP8 expression in whole uteri and the number of MMP8-expressing macrophages were decreased. An analysis of the comprehensive gene expression suggested that increased expression of fibroblast growth factors and decreased expression of an aquaporin may be related to the dilation of uterine glands in Esr2 KO mice, and reduced infiltration or differentiation into the macrophages with MMP8 expression may be involved with the collagen accumulation in Esr2 KO mice with age. Taken together, the absence of ESR2 constitutively disrupts estrogen signaling and promotes aging in the uterus via stimulation of epithelial cell proliferation and a decrease of MMP8-expressing macrophages.

The European Food Safety Authority (EFSA) has revised their estimate of the toxicity of bisphenol A (BPA) and, as a result, have recommended reducing the tolerable daily intake (TDI) by 20 000-fold. This would essentially ban the use of BPA in food packaging such as can liners, plastic food containers, and in consumer products. To come to this conclusion, EFSA used a systematic approach according to a pre-established protocol and included all guideline and nonguideline studies in their analysis. They found that Th-17 immune cells increased with very low exposure to BPA and used this endpoint to revise the TDI to be human health protective. A number of regulatory agencies including the European Medicines Agency (EMA) have written formal disagreements with several elements of EFSA's proposal. The European Commission will now decide whether to accept EFSA's recommendation over the objections of EMA. If the Commission accepts EFSA's recommendation, it will be a landmark action using knowledge acquired through independent scientific studies focused on biomarkers of chronic disease to protect human health. The goal of this Perspective is to clearly articulate the monumental nature of this debate and decision and to explain what is at stake. Our perspective is that the weight of evidence clearly supports EFSA's proposal to reduce the TDI by 20 000-fold.

We compared the influence of thyroid hormone‐disrupting chemicals (heptafluorobutanoic acid, PFBA and tris[1,3‐dichloro‐2‐propyl] phosphate, TDCPP) and thyroid hormone (3,3′,5‐triiodo‐L‐thyronine, T3) on swim bladder inflation and thyroid hormone‐related gene expression in Japanese medaka and zebrafish. The swim bladder of most larvae had inflated at 4 h post hatching (hph) in Japanese medaka and at 48 hph in zebrafish in controls. In both fish species, the swim bladder inflation was inhibited in larvae exposed to PFBA (lowest observed effect concentration [LOEC] in medaka: 40 mg/L; in zebrafish: 80 mg/L), TDCPP (LOEC in medaka: 1 mg/L; in zebrafish: 0.5 mg/L), and T3 (no inhibition in Japanese medaka; LOEC in zebrafish: 7.5 μg/L). We also examined the influence of PFBA, TDCPP, and T3 on the expression of thyroid stimulating hormone subunit beta (tshβ) or thyroid hormone receptor alpha (trα) and beta (trβ). No changes were observed in the expression of genes after PFBA and TDCPP exposure; however, T3 exposure upregulated trα and trβ expression in both fish species. When the results were compared between Japanese medaka and zebrafish, swim bladder inflation in both species was found to be inhibited by exposure to thyroid hormone‐disrupting chemicals. Our results show that inhibition of the swim bladder inflation at 4 hph in Japanese medaka and 48 hph in zebrafish is a potential indicator of thyroid hormone‐disturbing activity of chemicals.

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 among the Arthropoda and contain a wide variety of commercially important fishery species such as shrimps, lobsters and crabs (Order Decapoda), and keystone species of aquatic ecosystems such as water fleas (Order Branchiopoda). In terms of decapod sex determination and differentiation, previous approaches have attempted to elucidate their molecular components, to establish mono-sex breeding technology. Here, we overview reports describing the physiological functions of sex hormones regulating masculinization and feminization, and gene discovery by transcriptomics in decapod species. Moreover, this review summarizes the recent progresses of studies on the juvenile hormone-driven sex determination system of the branchiopod genus Daphnia, and then compares sex determination and endocrine systems between decapods and branchiopods. This review provides not only substantial insights for aquaculture research, but also the opportunity to re-organize the current and future trends of this field.

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 of the JH signaling pathway causes many physiological effects, the molecular basis for the structural feature and ligand binding properties of Daphnia Met are not fully understood. To study the ligand preference in terms of structural features of Daphnia Met, we built in silico homology models of the PAS-B domain of Daphnia Mets from cladoceran crustaceans, Daphnia pulex and D. magna. Structural comparison of two Daphnia Met PAS-B domain models revealed that the volume in the main cavity of D. magna Met was larger than that of D. pulex Met. Compared with insect Met, Daphnia Met had a less hydrophobic cavity due to polar residues in the core-binding site. Molecular docking simulations of JH and its analogs with Daphnia Met indicated that the interaction energies were correlated with each of the experimental values of in vivo JH activities based on male induction and in vitro Met-mediated transactivation potencies. Furthermore, in silico site-directed mutagenesis supported experimental findings that Thr292 in D. pulex Met and Thr296 in D. magna Met substitution to valine contribute to JH selectivity and differential species response. This study demonstrates that in silico simulations of Daphnia Met and its ligands may be a tool for predicting the ligand profile and cross species sensitivity.