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PubMed2003

Pigment cell organization in the hypodermis of zebrafish.

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.

Animals↗
PubMed1983

Biosynthesis of the photosynthetic membranes of Rhodopseudomonas sphaeroides.

The steady-state biosynthesis of the photosynthetic membrane (ICM) of Rhodopseudomonas sphaeroides has been reviewed. At moderate light intensities, 500 ft-c, preexisting ICM serves as the insertion matrix for newly synthesized membrane components. Whereas the bulk of the membrane protein, protein-pigment complexes, and pigments are inserted into preexisting ICM throughout the cell cycle, phospholipid is transferred from outside the ICM to the ICM only at the time of cell division. Because the site of cellular phospholipid synthesis is the cytoplasmic membrane, these results infer that despite the physical continuity of cytoplasmic membrane and ICM, there must exist between these membranous domains a "barrier" to the free diffusion of cellular phospholipid. The cyclical alternation in protein to phospholipid ratio of the ICM infers major structural and functional alternations, such as changes in the protein to lipid ratio of the membrane, specific density of the membrane, lipid structure within the membrane, and the rate of cyclic electron flow. When biochemical studies are correlated with detailed electron microscopic investigations we can further conclude that the number of photosynthetic units within the plane of the membrane can vary by nearly a factor of two over the course of the cell cycle. The average physical size of the photosynthetic units is constant for a given light intensity but inversely proportional to light intensity. The distribution of photosynthetic unit size classes within the membrane can be interpreted as suggesting that the "core" of the photosynthetic unit (reaction center plus fixed antenna complex) is inserted into the membrane coordinately as a structural entity. The variable antenna complex is, on the other hand, inserted independent of the "core" and randomly associates with both old and new core complexes. Finally, we conclude that there is substantial substructure to te distribution of photosynthetic units within the ICM, ie, they are highly ordered and exist in a defined spatial orientation to one another.

Bacterial Chromatophores↗
PubMed1984

Differential protein insertion into developing photosynthetic membrane regions of Rhodopseudomonas sphaeroides.

Previous studies have suggested that much of the B800-850 light-harvesting bacteriochlorophyll a-protein complex is inserted directly into the intracytoplasmic photosynthetic membrane of Rhodopseudomonas sphaeroides. In contrast, the B875 light-harvesting and reaction center complexes are assembled preferentially at peripheral sites of photosynthetic membrane growth initiation. The basis for this apparent site-specific polypeptide insertion was examined during the inhibition of RNA and protein syntheses. The pulse labeling of polypeptides at the membrane growth initiation sites was significantly less sensitive to inhibition by rifampicin, chloramphenicol, or kasugamycin than in the intracytoplasmic or outer membranes. This suggests increased stability for the translation machinery at these membrane invagination sites. Similar differential effects in polypeptide insertion were observed during inhibition of bacteriochlorophyll synthesis through deprival of delta-aminolevulinate to R sphaeroides mutant H-5, which requires this porphyrin precursor. The pulse-labeling patterns observed during the inhibition of both RNA and pigment syntheses were consistent with the uncoupling of polypeptide insertion into the membrane invagination sites from their growth and maturation into intracytoplasmic membranes.

Anti-Bacterial Agents↗