Miki Shimohigashi

Bisphenol AF Is a Full Agonist for the Estrogen Receptor ERα but a Highly Specific Antagonist for ERβ

Background Bisphenol AF has been acknowledged to be useful for the production of CF3-containing polymers with improved chemical, thermal, and mechanical properties. Because of the lack of adequate toxicity data, bisphenol AF has been nominated for comprehensive toxicological characterization. Objectives We aimed to determine the relative preference of bisphenol AF for the human nuclear estrogenic receptors ERα and ERβ and the bisphenol A–specific estrogen-related receptor ERRγ, and to clarify structural characteristics of receptors that influence bisphenol AF binding. Methods We examined receptor-binding activities of bisphenol AF relative to [3H]17β-estradiol (for ERα and ERβ) and [3H]bisphenol A (for ERRγ). Functional luciferase reporter gene assays were performed to assess receptor activation in HeLa cells. Results We found that bisphenol AF strongly and selectively binds to ERs over ERRγ. Furthermore, bisphenol AF receptor-binding activity was three times stronger for ERβ [IC50 (median inhibitory concentration) = 18.9 nM] than for ERα. When examined using a reporter gene assay, bisphenol AF was a full agonist for ERα. In contrast, it was almost completely inactive in stimulating the basal constitutive activity of ERβ. Surprisingly, bisphenol AF acted as a distinct and strong antagonist against the activity of the endogenous ERβ agonist 17β-estradiol. Conclusion Our results suggest that bisphenol AF could function as an endocrine-disrupting chemical by acting as an agonist or antagonist to perturb physiological processes mediated through ERα and/or ERβ.

Placenta Expressing the Greatest Quantity of Bisphenol A Receptor ERRγ among the Human Reproductive Tissues: Predominant Expression of Type-1 ERRγ Isoform

Estrogen-related receptor gamma (ERRgamma), one of the 48 human nuclear receptors, has a fully active conformation with no ligand. We recently demonstrated that ERRgamma binds strongly bisphenol A (BPA), one of the nastiest endocrine disruptors, and thus retaining ERRgammas high basal constitutive activity. A report that BPA accumulates in the human maternal-fetal placental unit has led us to hypothesize that a large amount of ERRgamma might exist in the human placenta. Here we report evidence that placenta indeed expresses ERRgamma exceptionally strongly. We first ascertained the presence of nine different ERRgamma mRNA variants and the resulting three ERRgamma protein isoforms. By real-time PCR, we estimated the relative amount of ERRgamma mRNA using total RNA extracts from human reproductive tissues. Placenta was found to express ERRgamma extremely highly. Among the three ERRgamma protein isoforms, placenta exclusively expresses the type-1 isoform, which possesses additional 23-mer amino-acid residues at the N-terminus of the ordinary ERRgamma. This N-terminal elongation was found to elevate by approximately 50% the basal constitutive activity of ERRgamma, as evidenced in the luciferase reporter gene assay. The present results suggest that BPA accumulates in the placenta by binding to ERRgamma.

Identificaton of UV, green and red receptors, and their projection to lamina in the cabbage butterfly, Pieris rapae

SummaryThe photoreceptors in the compound eye of a cabbage butterfly, Pieris rapae, were examined by conventional and intracellular-labeling electron microscopy by the use of the cobalt(III)-lysine complex as an ionized marker. Five types of spectral sensitivity were recorded intracellularly in electrophysiological experiments. They peaked at about 340, 380, 480, 560 and 620 nm, respectively. One of the distal retinula cells (R2) was a UV receptor, whereas the R4 distal retinula cell was a green receptor. The basal retinula cell, R9, was found to be a red receptor; it was localized near the basement membrane, having a bilobed cell body with an individual nucleus in each lobe. A small number of rhabdomere microvilli were present in a narrow cytoplasmic bridge connecting the two lobes. The axons of six retinula cells (R3–R8) in each ommatidium terminated at the cartridge in the lamina (short visual fiber), whereas those of the other three retinula cells, R1, R2 and R9, extended to the medulla (long visual fiber). The information from the UV and red receptors is therefore probably delivered directly to the medulla neurons, independent of that from the other spectral receptor types.

Characterization of PDF-immunoreactive neurons in the optic lobe and cerebral lobe of the cricket, Gryllus bimaculatus

Pigment-dispersing factor (PDF) is a neuropeptide playing important roles in insect circadian systems. In this study, we morphologically and physiologically characterized PDF-immunoreactive neurons in the optic lobe and the brain of the cricket Gryllus bimaculatus. PDF-immunoreactivity was detected in cells located in the proximal medulla (PDFMe cells) and those in the dorsal and ventral regions of the outer chiasma (PDFLa cells). The PDFMe cells had varicose processes spread over the frontal surface of the medulla and the PDFLa cells had varicose mesh-like innervations in almost whole lamina, suggesting their modulatory role in the optic lobe. Some of PDFMe cells had a hairpin-shaped axonal process running toward the lamina then turning back to project into the brain where they terminated at various protocerebral areas. The PDFMe cells had a low frequency spontaneous spike activity that was higher during the night and was often slightly increased by light pulses. Six pairs of PDF-immunoreactive neurons were also found in the frontal ganglion. Competitive ELISA with anti-PDF antibodies revealed daily cycling of PDF both in the optic lobe and cerebral lobe with an increase during the night that persisted in constant darkness. The physiological role of PDF is discussed based on these results.

A circadian neuropeptide, pigment-dispersing factor-PDF, in the last-summer cicada Meimuna opalifera: cDNA cloning and immunocytochemistry

Abstract Pigment-dispersing factor (PDF), an 18-amino acid neuropeptide, is a principal circadian neuromodulator functioning downstream of the insect brains circadian clock, modulating daily rhythms of locomotor activity. Recently, we found that PDF precursors of the cricket Gryllus bimaculatus comprise a nuclear localization signal (NLS). Moreover, the nuclear localization of PDF immunoreactivity and the trans-location of GFP-fused PDF precursor into the nucleus have both been demonstrated. These suggest a fundamental role for PDF peptide in the circadian clock system within the nucleus, in addition to its role in downstream neural events. In the present study, we carried out the cDNA cloning of PDF from adult brains of the last-summer cicada Meimuna opalifera, and found that an isolated clone (545 bp) encodes an ordinary PDF precursor protein. PDF peptide itself shows a high sequence identity (78–94%) and similarity (89–100%) to insect PDFs and also to the crustacean β-PDH peptides. The computer-assisted sequence analysis of PDF precursor revealed a possible translocation into the nucleus, despite the lack of a definite NLS-like sequence. Using immunocytochemistry, the optic lobes of M. opalifera revealed PDF-immunore-active neurons in both the medulla and lamina neuropiles. All these PDF cells exhibited prominent immunolabeling of both their perikarya and axons, but not their nuclei. Our results provide the first structural and immunocytochemical identification of PDF neurons in Hemiptera.

Structural isoforms of the circadian neuropeptide PDF expressed in the optic lobes of the cricket Gryllus bimaculatus: Immunocytochemical evidence from specific monoclonal antibodies

Pigment‐dispersing factor (PDF) is an 18‐mer peptide that acts as a principal neurotransmitter of the insect circadian clock. Our previous study, utilizing anti‐Uca β‐PDH polyclonal antibody (pAb) to immunolabel the optic lobe of the cricket Gryllus bimaculatus, suggested the existence of an alternative PDF‐like peptide in the outer cells of the first neuropile, or lamina (La), which were much less immunoreactive than the inner cells of the second neuropile, the medulla (Me). To obtain structural information about such a PDF‐like peptide, we prepared 10 anti‐Gryllus PDF monoclonal (mAb) and pAb antibodies and analyzed their detailed epitope specificities. The PDFMe and PDFLa inner cells and their axonal projections were clearly immunoreactive to all these antibodies, revealing the widespread immunocytochemical organization of the PDF system in the optic lobe, as seen previously with anti‐Uca β‐PDH pAb and anti‐Gryllus PDF mAb, the epitope structures of which were also clarified in this study. The lamina outer cells, which we found lacked a target pdf mRNA, displayed specific immunoreactivities, indicating that the cells contain a distinct PDF‐like peptide possessing both N‐ and C‐terminal structures. These cells were not immunolabeled by some other monoclonal antibodies, however, implying that the PDFLa outer cells have a PDF isoform peptide devoid of Asn at positions 6 and 16. This isoform was also identified in a varicose arborization in the lamina. These results suggest not only the structure of the peptide, but also the possibility of additional functions of this novel PDF isoform. J. Comp. Neurol. 499:404–421, 2006.

Molecular Cogs of the Insect Circadian Clock

Abstract During the last five years, enormous progress has been made in understanding the molecular basis of circadian systems, mainly by molecular genetic studies using the mouse and fly. Extensive evidence has revealed that the core clock machinery involves “clock genes” and “clock proteins” functioning as molecular cogs. These participate in transcriptional/translational feedback loops and many homologous clock-components in the fruit fly Drosophila are also expressed in mammalian clock tissues with circadian rhythms. Thus, the mechanisms of the central clock seem to be conserved across animal kingdom. However, some recent studies imply that the present widely accepted molecular models of circadian clocks may not always be supported by the experimental evidence.

The compound eye of Parnara guttata (Insecta, Lepidoptera, Hesperiidae): Fine structure of the ommatidium

SummaryThe fine structure of an ommatidium of a skipper butterfly, Parnara guttata, has been studied using the electron microscope. Each ommatidium has nine retinula cells, which were classified into three groups: two distal, six medial and one basal retinula cells. The rhabdomeres of the distal retinula cells are localized in the distal part of the rhabdom, while those of the six medial retinula cells appear throughout most of the rhabdom. The rhabdomere of the basal retinula cell occupies only the basal part of the rhabdom. The rhabdomeres of four medial cells are constructed of parallel microvilli, while fan-like microvilli form the rhabdomeres of other two medial retinula cells. The distal and basal retinula cells have rhabdomeres consisting of both parallel and fan-like microvilli. This is the first time the construction of the rhabdomeres of the distal and basal retinula cells has been described in such fine detail for a skipper butterfly. Nine retinula cell axons of each ommatidium extend to the first neuropile of the optic lobe, the lamina ganglionaris. No difference was found in the number of retinula cells of an ommatidium or the shape of the rhabdom between the dorsal and ventral regions of the compound eye.

Structural Analysis and Identification of Novel Isoforms of the Circadian Clock Gene period in the Silk Moth Bombyx mori

Abstract The molecular basis of the circadian clock is an autoregulatory feedback loop in which the PAS domain-containing protein PERIOD periodically inhibits its own transcription. In the present study on PERIOD of the silk moth Bombyx mori, we have cloned two distinct period mRNA homologues with different PAS domain sequences either with or without the pentapeptide GTQEK. A period cDNA fragment first amplified by PCR exhibited a 15 bp-deleted nucleotide sequence in the PAS domain, compared with the database sequence. A possible alternative splicing mechanism was examined by PCR analyses, and a 15 bp-inserted clone was also amplified. The entire sequences of these period α and period β isoforms were then determined by the 3′ and 5′ RACE methods. Isoform period α consists of a 3,324 bp oligonucleotide encoding 1,108 amino acid residues, whereas isoform period β comprises 3,309 bp corresponding to 1,103 amino acids. Isoforms period α and period β were found to be exactly identical except for the 15 bp deletion/insertion site. Such a pair of isoforms with a deletion/insertion sequence, namely two splice variants, has previously been reported only for the PERIOD proteins of the two honeybees, Apis mellifera and A. cerana. The occurrence of an alternative splicing mechanism in the B. mori period gene was hypothesized based on the genome structure recently clarified. Bombyx mori PERIOD α and β proteins are the isomers that reveal firstly the different PAS domain sequences.

A characteristic back support structure in the bisphenol A-binding pocket in the human nuclear receptor ERRγ.

The endocrine disruptor bisphenol A (BPA) affects various genes and hormones even at merely physiological levels. We recently demonstrated that BPA binds strongly to human nuclear receptor estrogen-related receptor (ERR) γ and that the phenol-A group of BPA is in a receptacle pocket with essential amino acid residues to provide structural support at the backside. This led BPA to bind to ERRγ in an induced-fit-type binding mode, for example, with a rotated motion of Val313 to support the Tyr326-binding site. A similar binding mechanism appears to occur at the binding site of the BPA phenol-B ring. X-ray crystal analysis of the ERRγ-ligand-binding domain/BPA complex suggested that the ERRγ receptor residues Leu342, Leu345, Asn346, and Ile349 function as intrinsic binding sites of the BPA phenol-B, whereas Leu265, Leu268, Ile310, Val313, Leu324, Tyr330, Lys430, Ala431, and His434 work as structural elements to assist these binding sites. In the present study, by evaluating the mutant receptors replaced by a series of amino acids, we demonstrated that a finely assembled structural network indeed exists around the two adjacent Leu342-Asn346 and Leu345-Ile349 ridges on the same α-helix 7 (H7), constructing a part of the binding pocket structure with back support residues for the BPA phenol-B ring. The results reveal that the double-layer binding sites, namely, the ordinary ligand binding sites and their back support residues, substantiate the strong binding of BPA to ERRγ. When ERRγ-Asn346 was replaced by the corresponding Gly and Tyr in ERRα and ERRβ, respectively, the binding affinity of BPA and even 4-hydroxytamxifen (4-OHT) is much reduced. Asn346 was found to be one of the residues that make ERRγ to be exclusive to BPA.