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Munakata K.,Tokyo Institute of Technology | Ookata K.,Tokyo Institute of Technology | Doi H.,Shimonoseki Marine Science Museum | Baba O.,Tokyo Medical and Dental University | And 3 more authors.
Biochemical and Biophysical Research Communications | Year: 2012

Luminal surface of the swimbladder is covered by gas gland epithelial cells and is responsible for inflating the swimbladder by generating O 2 from Root-effect hemoglobin that releases O 2 under acidic conditions. Acidification of blood is achieved by lactic acid secreted from gas gland cells, which are poor in mitochondria but rich in the glycolytic activity. The acidic conditions are locally maintained by a countercurrent capillary system called rete mirabile. To understand the regulation of anaerobic metabolism of glucose in the gas gland cells, we analyzed the glucose transporter expressed there and the fate of ATP generated by glycolysis. The latter is important because the ATP should be immediately consumed otherwise it strongly inhibits the glycolysis rendering the cells unable to produce lactic acid anymore. Expression analyses of glucose transporter (glut) genes in the swimbladder of fugu (Takifugu rubripes) by RT-PCR and in situ hybridization demonstrated that glut1a and glut6 are expressed in gas gland cells. Immunohistochemical analyses of metabolic enzymes demonstrated that a gluconeogenesis enzyme fructose-1,6-bisphosphatase (Fbp1) and a glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Gapdh) are highly expressed in gas gland cells. The simultaneous catalyses of glycolysis and gluconeogenesis reactions suggest the presence of a futile cycle in gas gland cells to maintain the levels of ATP low and to generate heat that helps reduce the solubility of O 2. © 2011 Elsevier Inc..

Yamauchi T.,Toyama Institute of Health | Doi H.,Shimonoseki Marine Science Museum | Wada M.,JF Iorigawa | Nagasawa K.,Hiroshima University
Nature and Human Activities | Year: 2010

Limnotrachelobdella okae was collected from Kadogawa Cove (the western North Pacific), Miyazaki Prefecture, Kyushu (single specimen), and from the Sea of Japan of Shimonoseki, Yamaguchi Prefecture, Honshu, Japan (two specimens). These collections represent the westernmost record of L. o£ae from the Sea of Japan and the southernmost record of its total geographical distribution, respectively. In Kadogawa Cove, the leech was found attached to the skin of a Japanese seaperch Lateolabrax japonicus. A leech from off Shimonoseki was attempted to infect marine fishes kept in an aquarium tank, but it did not parasitize them and died 15 days after collection.

Uehara M.,Tottori University | Hosaka Y.Z.,Tottori University | Doi H.,Shimonoseki Marine Science Museum | Sakai H.,National Fisheries University
Journal of Morphology | Year: 2015

In teleosts, the spinal cord generally extends along the entire vertebral canal. The Tetraodontiformes, in which the spinal cord is greatly reduced in length with a distinct long filum terminale and cauda equina, have been regarded as an aberration. The aims of this study are: 1) to elucidate whether the spinal cord in all tetraodontiform fishes shorten with the filum terminale, and 2) to describe the gross anatomical and histological differences in the spinal cord among all families of the Tetraodontiformes. Representative species from all families of the Tetraodontiformes, and for comparison the carp as a common teleost, were investigated. In the Triacanthodidae, Triacanthidae, and Triodontidae, which are the more ancestral taxa of the Tetraodontiformes, the spinal cord extends through the entire vertebral canal. In the Triacanthidae and Triodontidae, the caudal half or more spinal segments of the spinal cord, however, lack gray matter and consist largely of nerve fibers. In the other tetraodontiform families, the spinal cord is shortened forming a filum terminale with the cauda equina, which is prolonged as far as the last vertebra. The shortened spinal cord is divided into three groups. In the Ostraciidae and Molidae, the spinal cord tapers abruptly at the cranium or first vertebra forming a cord-like filum terminale. In the Monacanthidae, Tetraodontidae, and Diodontidae, it abruptly flattens at the rostral vertebrae forming a flat filum terminale. The spinal cord is relatively longer in the Monacanthidae than that in the other two families. It is suggested by histological features of the flat filum terminale that shortening of the spinal cord in this group progresses in order of the Monacanthidae, Tetraodontidae, and Diodontidae. In the Balistidae and Aracanidae, the cord is relatively long and then gradually decreased in dorso-ventral thickness. J. Morphol. 276:290-300, 2015. © 2014 Wiley Periodicals, Inc.

Tanaka K.,Tokai University | Shiina T.,Tokai University | Tomita T.,Hokkaido University | Suzuki S.,Tokai University | And 9 more authors.
BioMed Research International | Year: 2013

Hexanchiformes is regarded as a monophyletic taxon, but the morphological and genetic relationships between the five extant species within the order are still uncertain. In this study, we determined the whole mitochondrial DNA (mtDNA) sequences of seven sharks including representatives of the five Hexanchiformes, one squaliform, and one carcharhiniform and inferred the phylogenetic relationships among those species and 12 other Chondrichthyes (cartilaginous fishes) species for which the complete mitogenome is available. The monophyly of Hexanchiformes and its close relation with all other Squaliformes sharks were strongly supported by likelihood and Bayesian phylogenetic analysis of 13,749 aligned nucleotides of 13 protein coding genes and two rRNA genes that were derived from the whole mDNA sequences of the 19 species. The phylogeny suggested that Hexanchiformes is in the superorder Squalomorphi, Chlamydoselachus anguineus (frilled shark) is the sister species to all other Hexanchiformes, and the relations within Hexanchiformes are well resolved as Chlamydoselachus, (Notorynchus, (Heptranchias, (Hexanchus griseus, H. nakamurai))). Based on our phylogeny, we discussed evolutionary scenarios of the jaw suspension mechanism and gill slit numbers that are significant features in the sharks. © 2013 Keiko Tanaka et al.

Islam Z.,Tokyo Institute of Technology | Hayashi N.,Tokyo Institute of Technology | Inoue H.,University of Tokyo | Umezawa T.,Tokyo Institute of Technology | And 6 more authors.
American Journal of Physiology - Regulatory Integrative and Comparative Physiology | Year: 2014

The kidney of marine teleosts isthe major site of Mg2 excretion and produces urine with a highMg2+ concentration. However, the transporters involved in Mg2+ excretion are poorly understood. The cyclin M (Cnnm; also known as ancient conserved domain protein) family comprises membrane pro-teins homologous to the bacterial Mg2+ and Co2+ efflux protein, CorC. To understand the molecular mechanism of Mg2+ homeostasis in marine teleosts, we analyzed the expression of the Cnnm family genes in the seawater (SW) pufferfish, torafugu (Takifugu rubripes), and the closely related euryhaline species, mefugu (Takifugu obscurus). Database mining and phylogenetic analysis indicated that the Takifugu genome contains six members of the Cnnm family: two orthologs of Cnnm1, one of Cnnm2, one of Cnnm3, and two of Cnnm4. RT-PCR analyses indicated that Cnnm2, Cnnm3, and Cnnm4a are expressed in the kidney, whereas other members are mainly expressed in the brain. Renal expression of Cnnm3 was upregulated in SW mefugu, whereas renal expression of Cnnm2 was upregulated in freshwater (FW) mefugu. No significant difference was observed in renal expression of Cnnm4a between SW and FW mefugu. In situ hybridization and immunohistochemical analyses of the SW mefugu kidney revealed that Cnnm3 is expressed in the proximal tubule, and its product localizes to the lateral membrane. When Cnnm3 wasexpressed in Xenopus laevis oocytes, whole cellular Mg2+ contentand free intracellular Mg2+ activity significantly decreased. Theseresults suggest that Cnnm3 is involved in body fluid Mg2+ homeostasis in marine teleosts. © 2014 the American Physiological Society.

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