Zebrafish have a characteristic horizontal-stripe pigment pattern made by a specific distribution of three types of pigment cells: melanophores, xanthophores, and iridophores. This pattern is a valuable model to investigate how the spatial patterns form during animal development. Although recent findings suggest that the interactions among the pigment cells play a key role, the particular details of these interactions have not yet been clarified. In this report, we performed transmission electron microscopic study to show the distribution, conformation, and how the cells contact with each other in the hypodermis. We found that the pigment cells form complex but ordered, layered structures in both stripe and interstripe regions. The order of the layered structures is kept strictly all through the hypodermal regions. Our study will provide basic information to investigate the mechanism of pigment pattern formation in zebrafish. Developmental Dynamics 227:497-503, 2003.

Stressed cells release ATP, which participates in neurodegenerative processes through the specific ligation of P2RX7 purinergic receptors. Here, we demonstrate that extracellular ATP and the more specific P2RX7 agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP, both induce photoreceptor cell death when added to primary retinal cell cultures or when injected into the eyes from wild-type mice, but not into the eyes from P2RX7(-/-) mice. Photoreceptor cell death was accompanied by the activation of caspase-8 and -9, translocation of apoptosis-inducing factor from mitochondria to nuclei, and TUNEL-detectable chromatin fragmentation. All hallmarks of photoreceptor apoptosis were prevented by premedication or co-application of Brilliant Blue G, a selective P2RX7 antagonist that is already approved for the staining of internal limiting membranes during ocular surgery. ATP release is up-regulated by nutrient starvation in primary retinal cell cultures and seems to be an initializing event that triggers primary and/or secondary cell death via the positive feedback loop on P2RX7. Our results encourage the potential application of Brilliant Blue G as a novel neuroprotective agent in retinal diseases or similar neurodegenerative pathologies linked to excessive extracellular ATP.

To obtain insights into the cardiomyogenic potential of hematopoietic tissue, we intravenously (i.v.) injected purified hematopoietic stem/progenitor cells into newborn recipients that may fully potentiate the developmental plasticity of stem cells. Transplantation of mouse bone marrow (BM) lineage antigen-negative (Lin-) cells resulted in the generation of the cells that displayed cardiomyocyte-specific antigenic profiles and contractile function when transplanted into syngeneic newborn recipients. To clarify the mechanism underlying the cardiomyogenic potential, green fluorescent protein (GFP)-labeled BM Lin-ScaI+ hematopoietic progenitors were transplanted into neonatal mice constitutively expressing cyan fluorescence protein (CFP). Lambda image acquisition and linear unmixing analysis using confocal microscopy successfully separated GFP and CFP, and revealed that donor GFP+ cardiomyocytes coexpressed host-derived CFP. We further reconstituted human hemopoietic- and immune systems in mice by injecting human cord blood (CB)-derived Lin-CD34+CD38- hematopoietic stem cells (HSCs) into neonatal T cell(-)B cell(-)NK cell- immune-deficient NOD/SCID/IL2rgamma(null) mice. Fluoroescence in situ hybridization analysis of recipient cardiac tissues demonstrated that human and murine chromosomes were colocalized in the same cardiomyocytes, indicating that cell fusion occurred between human hematopoietic progeny and mouse cardiomyocytes. These syngeneic- and xenogeneic neonatal transplantations provide compelling evidence that hematopoietic stem/progenitor cells contribute to the postnatal generation of cardiomyocytes through cell fusion, not through transdifferentiation.

Weil's disease, the most severe form of leptospirosis, is characterized by jaundice, haemorrhage and renal failure. The mechanisms of jaundice caused by pathogenic Leptospira remain unclear. We therefore aimed to elucidate the mechanisms by integrating histopathological changes with serum biochemical abnormalities during the development of jaundice in a hamster model of Weil's disease. In this work, we obtained three-dimensional images of infected hamster livers using scanning electron microscope together with freeze-cracking and cross-cutting methods for sample preparation. The images displayed the corkscrew-shaped bacteria, which infiltrated the Disse's space, migrated between hepatocytes, detached the intercellular junctions and disrupted the bile canaliculi. Destruction of bile canaliculi coincided with the elevation of conjugated bilirubin, aspartate transaminase and alkaline phosphatase levels in serum, whereas serum alanine transaminase and γ-glutamyl transpeptidase levels increased slightly, but not significantly. We also found in ex vivo experiments that pathogenic, but not non-pathogenic leptospires, tend to adhere to the perijunctional region of hepatocyte couplets isolated from hamsters and initiate invasion of the intercellular junction within 1 h after co-incubation. Our results suggest that pathogenic leptospires invade the intercellular junctions of host hepatocytes, and this invasion contributes in the disruption of the junction. Subsequently, bile leaks from bile canaliculi and jaundice occurs immediately. Our findings revealed not only a novel pathogenicity of leptospires, but also a novel mechanism of jaundice induced by bacterial infection.

Strain Eri-1T was isolated from a water sample on the campus of Kyushu University, Fukuoka, Japan. The motility and morphology of the isolate were similar to those of members of the genus Leptospira , but the spiral structure of the isolate was sharper under dark-field microscopy. Cells were 10.6±1.3 µm long and 0.2 µm in diameter, with a wavelength of 0.9 µm and an amplitude of 0.4 µm. Strain Eri-1T grew in Korthof’s medium at both 13 and 30 °C, and also in the presence of 8-azaguanine. 16S rRNA gene-based phylogenetic analysis placed strain Eri-1T within the radiation of the genus Leptospira where it formed a unique lineage within the clade of the known saprophytic species of the genus Leptospira . The strain was not pathogenic to hamsters. Strain Eri-1T exhibited low levels (11.2–12.6 %) of similarity by DNA–DNA hybridization to the three most closely related species of the genus Leptospira . The DNA G+C content of the genome of strain Eri-1T was 42.5±0.1 mol%. These results suggest that strain Eri-1T represents a novel species of the genus Leptospira , for which the name Leptospira idonii sp. nov. is proposed. The type strain is Eri-1T ( = DSM 26084T = JCM 18486T).