Growth of carbon nanotube field emitters on single strand carbon fiber: a linear electron source

The multi-stage effect has been revisited through growing carbon nanotube field emitters on single strand carbon fiber with a thickness of 11 µm. A prepared linear electron source exhibits a turn-on field as low as 0.4 V µm(-1) and an extremely high field enhancement factor of 19,300, when compared with those results from reference nanotube emitters grown on flat silicone wafer; 3.0 V µm(-1) and 2500, respectively. In addition, we introduce a novel method to grow nanotubes uniformly around the circumference of carbon fibers by using direct resistive heating on the continuously feeding carbon threads. These results open up not only a new path for synthesizing nanocomposites, but also offer an excellent linear electron source for special applications such as backlight units for liquid crystal displays and multi-array x-ray sources.

Heteropolymorphism of mitochondrial NADH dehydrogenase subunit 3 gene for the population analysis of chum salmon, Oncorhynchus keta

Mitochondrial DNAs (mtDNAs) has been frequently used as genetic markers for the population genetic studies. In this study we used chum salmon (Oncorhynchus keta) from Korea, Japan andAmerica, and compared their mitochondrial NADH dehydrogenase subunit 3 (ND3) genes by DNA sequence analysis. Sequence variation was studied in the ND3 among total 11 individuals from three populations. The ND3 gene was amplified by PCR targeting parts of cytochrome oxidase III gene (COIII) and NADH dehydrogenase subunit 4L gene (ND4L). ND3 gene sequence, encoded 752 bps, presented some genetic variation in the chum salmon populations. The observed nucleotide variations inferred the distinct genetic differentiation of American salmons from Korean and Japanese chum salmons. Six sites of single nucleotide polymorphism (SNP) were explored in the ND3 locus. Denaturing gradient gel electrophoresis analysis also showed a clear heterogenous band in American salmons compared to Asian salmons.

Silencing mediator of retinoid and thyroid hormone receptors and activating signal cointegrator-2 as transcriptional coregulators of the orphan nuclear receptor Nur77

For the orphan nuclear receptor subfamily that includes Nur77 (NGFI-B), Nurr1, and NOR-1, no transcriptional coregulators have been identified thus far. In this report, we found that Ca(2+)/calmodulin-dependent protein kinase IV enhances Nur77 transactivation in cotransfections either alone or in synergy with AF2dependent coactivator ASC-2, whereas corepressor silencing mediator for retinoid and thyroid hormone receptors (SMRT) is repressive. Interestingly, Nur77 interacted with SMRT but did not directly bind ASC-2, and accordingly, the putative AF2 core domain of Nur77 did not affect the Nur77 transactivation. SMRT harbors transferable repression domains that associate with various histone deacetylases. Surprisingly, histone deacetylase inhibitor trichostatin A was unable to block the repressive effect of SMRT while dramatically stimulating the Nur77 transactivation. These results suggest that SMRT and ASC-2 are specific coregulators of Nur77 and that SMRT may dynamically compete with a putative adaptor molecule, which links ASC-2 to Nur77, for the identical binding sites within Nur77 in vivo.

Ca2+/calmodulin-dependent protein kinase IV stimulates nuclear factor-kappa B transactivation via phosphorylation of the p65 subunit

Calmodulin-dependent protein kinase IV (CaMKIV) is a key mediator of Ca(2+)-induced gene expression. In this study, CaMKIV was found to directly associate with and phosphorylate the nuclear factor-kappaB (NFkappaB) component p65 both in vitro and in vivo. The phosphorylation of p65 by CaMKIV resulted in recruitment of transcription coactivator cAMP-response element-binding protein-binding protein and concomitant release of corepressor silencing mediator for retinoid and thyroid hormone receptors, as demonstrated by the glutathione S-transferase pull down and mammalian two hybrid assays. In addition, cotransfection of CaMKIV resulted in cytosolic translocation of the silencing mediator for retinoid and thyroid hormone receptors. Consistent with these results, cotransfected CaMKIV dramatically stimulated the NFkappaB transactivation in mammalian cells. From these results, NFkappaB is suggested to be a novel downstream effector molecule of CaMKIV.

Regulation of gonadotropin beta subunit gene expression by testosterone and gonadotropin-releasing hormones in the goldfish, Carassius auratus

Sex steroids differentially regulate gonadotropin (GTH) beta subunits (FSHbeta and LHbeta) gene expression in the pituitary of goldfish: a strong in vivo inhibitory effect on FSHbeta mRNA production, but a weak stimulatory effect on LHbeta in sexually immature and recrudescent fish. In the present study, to examine a direct effect of testosterone (T) and gonadotropin-releasing hormone (GnRH) on the mRNA levels of FSHbeta and LHbeta subunits in the pituitary, in vitro experiments were performed using dispersed pituitary cells of sexually immature, recrudescent, mature and regressed goldfish. T treatment in vitro did not significantly decrease FSHbeta mRNA levels, but increased that of LHbeta only in the cells of immature fish. Salmon-type GnRH increased FSHbeta mRNA levels in cells of mature fish, but decreased the levels in cells of sexually regressed fish. From these results, it was suggested that: (1) in vivo effect of sex steroids on gene expression of GTH beta subunits is not always exerted on the pituitary; and (2) the different responses of GTH beta subunits by sex steroids between in vivo and in vitro are partly due to a complex pathway through hypothalamic factors, such as GnRH, in the case of in vivo.

Isolation and characterization of the goldfish thyrotropin beta subunit gene including the 5'-flanking region

The complete gene encoding the beta subunit of thyrotropin (thyroid-stimulating hormone, TSH) was isolated from a goldfish genomic library. The goldfish TSHbeta subunit gene, which is approximately 2.0 kilobase pairs (kb) in length, consisted of three exons and two introns. The first intron was much longer (0.89 kb) than the second intron (0.3 kb) as are TSHbeta genes in mammalian species. On the basis of the location of the first intron, the goldfish TSHbeta gene belongs to the mammalian TSHbeta/FSHbeta gene group, which is distinct from the LHbeta group. Inspection of the 5'-flanking and exon 1 regions of the goldfish TSHbeta gene (1.2 kb) revealed the presence of several putative cis-acting elements, including the negative triiodothyronine (T(3))-responsive element (nTRE), Pit-1 element, and GATA-2 element. Comparison of the goldfish sequence with mammalian TSHbeta promoter sequences showed an identical region, nTRE, in the first exon-intron junction region. An in vitro study using dispersed goldfish pituitary cells showed that T(3) treatment (20 ng/ml) suppressed the TSHbeta mRNA level in the cells. These data indicate that (1) the basic structure of TSHbeta genes is highly conserved in vertebrates and that (2) T(3) acts directly on the pituitary and inhibits TSHbeta gene expression in goldfish, probably via the nTRE in the TSHbeta gene.

Seasonal changes in mRNA levels of gonadotropin and thyrotropin subunits in the goldfish, Carassius auratus

Seasonal changes in the mRNA levels of glycoprotein alpha, gonadotropin (GTH) Ibeta and IIbeta, and thyrotropin (thyroid-stimulating hormone (TSH)) beta subunits in the pituitary of goldfish were quantified by Northern blot analysis and laser densitometry. Reproductive development and thyroid activity were monitored by measuring gonadosomatic index, plasma GTH II, testosterone (T), estradiol, 11-ketotestosterone, and thyroid hormones (T4 and T3). Plasma GTH II and steroids showed characteristic increases, while plasma thyroid hormones levels, in general, decreased in association with the reproductive period. In females, the mRNA levels of the alpha, GTH Ibeta, and GTH IIbeta subunits increased synchronously during early spawning period (April) and then decreased during ovarian regression (August). In males, the levels of the alpha and GTH IIbeta subunits showed changes similar to those in females, but the GTH Ibeta mRNA levels showed only a small increase during the late spawning period (May). In both sexes, TSHbeta mRNA levels were high during winter to early spring (February and April) and low during late spring to summer (May and August). These results suggest that in goldfish the gonadotropins may be synthesized synchronously in order for asynchronous gametogenesis to take place. Additionally, the data suggest a negative feedback relationship between synthesis of the TSHbeta subunit and the thyroid hormones.

Structural and expression analyses of gonadotropin Ibeta subunit genes in goldfish (Carassius auratus)

Gonadotropin (GTH) is a pituitary glycoprotein hormone that regulates gonadal development in vertebrates. In teleosts, it is considered that two types of GTH, GTH I (follicle-stimulating hormone-like GTH) and GTH II (luteinizing hormone-like GTH), are produced in the pituitary, and their molecules are comprised of common alpha and distinct beta subunits. In this study, we describe the complete structure and 5'-flanking regulatory region of two distinct genes encoding GTH Ibeta in goldfish, Carassius auratus. The two goldfish GTH Ibeta genes, gfGTHIbeta-1 and gfGTHIbeta-2, span 1719 and 1545 base pairs (bp) nucleotides, respectively, and there is a high sequence identity (92.1%) between the coding regions. Both genes consist of three exons separated by two introns as in mammalian FSH beta genes. The locations of the first intron and second intron showed a well-conserved pattern similar to those of mammalian FSH beta genes. Inspection of the 5'-flanking region of the gfGTHIbeta-1 and gfGTHIbeta-2 (approximately 1.4 and 1.1kb, respectively) revealed the presence of several putative cis-acting elements, including the gonadotrope-specific element, gonadotropin-releasing hormone responsive element, and half steroid hormone responsive elements. Interestingly, some of their elements were located contiguously between -187 and -124bp upstream from a TATAA sequence. Reverse transcription polymerase chain reaction confirmed that these two genes are expressed in the pituitary of individual fish. These results, taken together, demonstrate that there are at least two functional genes encoding GTH Ibeta, probably due to the tetraploidy of goldfish. The unique locations of the cis-acting elements in the GTH Ibeta genes suggest they may be involved in the expression of the goldfish GTH Ibeta gene.

Immunohistochemical and Ultrastructural characterization of the terminal nerve ganglion cells of the ayu, Plecoglossus altivelis (Salmoniformes, Teleostei)

BACKGROUND

Little is known on the cytological properties of the terminal nerve ganglion (TNG) cells in teleosts (Demski, 1993. Acta Anat., 148:81-95).

MATERIALS AND METHODS

To characterize the TNG cells of a salmonoid fish, Plecoglossus altivelis, we adopted immunohistochemistry and transmission electron microscopy (TEM).

RESULTS

The majority of the TNG cells formed a compact mass halfway between the olfactory sac and the olfactory bulb, whereas a few cells were scattered in the ventromedial region of the olfactory bulb. The cell had a voluminous perikaryon that was positive to antisera against gonadotropin-releasing hormone (GnRH), molluscan cardioexcitatory tetrapeptide (FM-RFamide), and neuropeptide Y (NPY). Immunostaining of consecutive sections with each antiserum showed the coexistence of these antigens in the same cells and their processes. Most of the processes originating from the cells projected centrally to the basal forebrain, including the optic nerve. With TEM, the cells revealed a peptidergic nature, i.e., the presence of abundant granular endoplasmic reticula and well-developed Golgi bodies in association with vesicles that were 70-100 nm in diameter. Occasionally, the cells adjoined one another directly without the intervention of glial sheets. Synaptic contacts were frequent in the proximal region of the processes, where thin lateral processes of the cells and axon terminals of unknown origin were intermingled with each other. Terminal buttons being engulfed by the soma were commonly seen.

CONCLUSIONS

The TNG cells of the salmonoid fish share many cytological characteristics with the cells of the nucleus olfactoretinalis of advanced teleosts such as acanthopterygians.

Distribution of neuropeptide Y and gonadotropin-releasing hormone immunoreactivities in the brain and hypophysis of the ayu, Plecoglossus altivelis (Teleostei)

This paper reports on the distribution, relationship and seasonal variations of neuropeptide Y (NPY)-like and gonadotropin-releasing hormone (GnRH)-like immunoreactants in the brain and hypophysis of the bony fish, the ayu Plecoglossus altivelis. NPY-like immunoreactivity was widely distributed in the brain: labeled cells were found in the nervus terminalis, the nucleus entopeduncularis, the habenula, the nucleus preopticus periventricularis, the nucleus tuberis lateralis, the mediodorsal hypothalamus, the dorsal tegmentum, and other sites. NPY fibers were considerably dense in the telencephalon and hypothalamus, and innervated the hypophysis. GnRH-positive cells occurred in the nervus terminalis and were sparsely distributed in the preoptic and tuberal areas of the hypothalamus. GnRH fibers were found in various regions of the brain. They were relatively dense in the hypothalamus, showing a local concentration in the middle region of the neurohypophysis. The GnRH-positive cells and fibers in the hypothalamo-hypophyseal complex increased in density around the spawning season. In tandem with gonadal maturation, NPY labeling in the cells of the nucleus tuberis lateralis became intense concomitantly with an increase in the labeled varicosities in the middle region of the neurohypophysis. Double immunostaining showed that NPY fibers were closely apposed to GnRH cells in the preoptic area. These results suggest a correlative involvement of NPY and GnRH in the control of the hypophyseal gonadotropic function of the ayu.