The pigmentary system of developing axolotls

Development ◽  
1986 ◽  
Vol 95 (1) ◽  
pp. 117-130
Author(s):  
S. K. Frost ◽  
L. G. Epp ◽  
S. J. Robinson
Keyword(s):  
Electron Micrographs ◽  
Biosynthetic Pathway ◽  
Ambystoma Mexicanum ◽  
Pigment Cells ◽  
Transmission Electron Micrographs ◽  
Electron Microscopic ◽  
Mexican Axolotl ◽  
Transmission Electron ◽  
Pteridine Biosynthesis

The axanthic mutant in the Mexican axolotl (Ambystoma mexicanum) was analysed with respect to the differentiation of pigment cells. Transmission electron micrographs revealed the presence of melanophores and cells that are described as unpigmented xanthophores in axanthic skin. Iridophores apparently failed to differentiate in axanthic axolotls (a pattern similar to that observed in melanoid axolotls). Chromatographic analyses of skin extracts confirmed that there are no pteridines (xanthophore pigments) in axanthic skin, suggesting that the axanthic gene may affect pteridine biosynthesis at some point early in the biosynthetic pathway. Why iridophores fail to differentiate in these animals is not known, but this, too, may be related to an inability to synthesize pigments properly. Xanthophore and iridophore pigments both presumably derive from purine precursors. Finally, all axanthic animals were found to be infected by a virus. Electron microscopic results demonstrated the presence of numerous macrophages in the dermis of the skin, occupying positions typical of pigment cells. The virus was localized primarily in macrophages, but was also observed in pigment cells. The virus is, as yet, uncharacterized but is thought to contribute to the low survivability of axanthic adults.

The pigmentary system of developing axolotls

Development ◽  
1984 ◽  
Vol 81 (1) ◽  
pp. 127-142
Author(s):  
S. K. Frost ◽  
L. G. Epp ◽  
S. J. Robinson
Keyword(s):  
Structural Characteristics ◽  
Cell Types ◽  
Ambystoma Mexicanum ◽  
Pigment Cells ◽  
Similar Data ◽  
Wild Type ◽  
Transmission Electron ◽  
Pteridine Biosynthesis ◽  
Development Proceeds ◽  
Chemical Evidence

The melanoid mutant in the Mexican axolotl (Ambystoma mexicanum) is analysed with respect to the differentiation of pigment cells. Pigment cells were observed with the transmission electron microscope in order to determine any unusual structural characteristics and to determine what happens to each of the cell types as development proceeds. Chemical analysis of pteridine pigments was also carried out, and changes in pteridine biosynthesis were found to correlate well with changes in xanthophore morphology and number. In melanoid axolotls, as development proceeds, melanophore numbers increase, xanthophores decrease, and iridophores fail to differentiate at all. This is considered to result from: (a) conversion of xanthophores (that are present in young larvae) to melanophores; (b) the gradual programming of the majority of chromatoblasts to become, exclusively, melanophores, and (c) the failure of some chromatoblasts (possibly iridoblasts) to differentiate altogether. The ultrastructural and chemical evidence presented in this study is compared to similar data for wild-type axolotls, and a mechanism regarding how the melanoid gene might act is suggested.

The pigmentary system of developing axolotls

Development ◽  
1984 ◽  
Vol 81 (1) ◽  
pp. 105-125
Author(s):  
S. K. Frost ◽  
L. G. Epp ◽  
S. J. Robinson
Keyword(s):  
Developmental Stages ◽  
Pigment Cell ◽  
Cell Types ◽  
Ambystoma Mexicanum ◽  
Pigment Cells ◽  
Wild Type ◽  
Cell Type ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Mutant Phenotypes

A biochemical and transmission electron microscopic description of the wild-type pigment phenotype in developing Mexican axolotls (Ambystoma mexicanum) is presented. There are three pigment cell types found in adult axolotl skin - melanophores, xanthophores and iridophores. Both pigments and pigment cells undergo specific developmental changes in axolotls. Melanophores are the predominant pigment cell type throughout development; xanthophores occur secondarily and in fewer numbers than melanophores; iridophores do not appear until well into the larval stage and remain thereafter as the least frequently encountered pigment cell type. Ultrastructural differences in xanthophore organelle (pterinosome) structure at different developmental stages correlate with changes in the pattern of pteridine biosynthesis. Sepiapterin, a yellow pteridine, is present in larval axolotl skin but not in adults. Ribofiavin (also yellow) is present in minimal quantities in larval skin and large quantities in adult axolotl skin. Pterinosomes undergo a morphological “reversion” at some point prior to or shortly after axolotls attain sexual maturity. Correlated with the neotenic state of the axolotl, certain larval pigmentary features are retained throughout development. Notably, the pigment cells remain scattered in the dermis such that no two pigment cell bodies overlap, although cell processes may overlap. This study forms the basis for comparison of the wild type pigment phenotype to the three mutant phenotypes-melanoid, axanthic and albino-found in the axolotl.

Phase contrast and electron microscopic studies on the nuclear apparatus of Escherichia coli

1953 ◽  
Vol 141 (903) ◽  
pp. 199-203 ◽  
Keyword(s):  
Escherichia Coli ◽  
Electron Micrographs ◽  
Electron Scattering ◽  
Phase Contrast ◽  
Transmission Electron Micrographs ◽  
Direct Transmission ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Microscopic Studies

Phase microscopic studies on Escherichia coli indicate that the contrast difference between the cytoplasmic and nuclear sites varies with the age of the culture. It is maximum with bacteria of 1 to 2 h growth and then gradually diminishes with age, vanishing in bacteria older than 9 h. Direct-transmission electron micrographs show that the nuclear sites are of smaller electron scattering power than the cytoplasm. Micrographs of shadowed bacterial replicas provide evidence of depressions in the nuclear sites.

Radial mass analysis of unstained STEM images of molluscan hemocyanins

1990 ◽  
Vol 48 (3) ◽  
pp. 810-811
Author(s):  
M.G. Hamilton ◽  
T.T. Herskovits ◽  
J.S. Wall
Keyword(s):  
Image Analysis ◽  
Hollow Cylinder ◽  
Electron Micrographs ◽  
Side View ◽  
Mass Analysis ◽  
Mass Measurements ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Transmission Electron Microscopic ◽  
Microscopic Studies

The hemocyanins of molluscs are aggregates of a cylindrical decameric subparticle that assembles into di-, tri-, tetra-, penta-, and larger multi-decameric particles with masses that are multiples of the 4.4 Md decamer. Electron micrographs of these hemocyanins typically show the particles with two profiles: circular representing the cylinder viewed from the end and rectangular representing the side-view of the hollow cylinder.The model proposed by Mellema and Klug from image analysis of a didecameric hemocyanin with the two decamers facing one another with collar (closed) ends outward fits the appearance of side-views of the negatively-stained cylinders. These authors also suggested that there might be caps at the ends. In one of a series of transmission electron microscopic studies of molluscan hemocyanins, Siezen and Van Bruggen supported the Mellema-Klug model, but stated that they had never observed a cap component. With STEM we have tested the end cap hypothesis by direct mass measurements across the end-views of unstained particles.

scholarly journals Identifying Atoms in High Resolution Transmission Electron Micrographs Using a Deep Convolutional Neural Net

2018 ◽  
Vol 24 (S1) ◽  
pp. 512-513 ◽  
Author(s):  
Jakob Schiøtz ◽  
Jacob Madsen ◽  
Pei Liu ◽  
Ole Winther ◽  
Jens Kling ◽  
...  
Keyword(s):  
High Resolution ◽  
Electron Micrographs ◽  
Transmission Electron Micrographs ◽  
Neural Net ◽  
Transmission Electron

Transmission electron microscopic study of antennal sensilla of the female black fly, Simulium arcticum (IIL-3; IIS-10.11) (Diptera: Simuliidae)

1990 ◽  
Vol 68 (7) ◽  
pp. 1443-1453 ◽  
Author(s):  
J. F. Sutcliffe ◽  
E. G. Kokko ◽  
J. L. Shipp
Keyword(s):  
Electron Micrographs ◽  
Host Location ◽  
Scanning Electron Micrographs ◽  
Antennal Sensilla ◽  
Electron Microscopic ◽  
Olfactory Sensilla ◽  
Transmission Electron Microscopic Study ◽  
Sensilla Trichodea ◽  
Transmission Electron ◽  
Transmission Electron Microscopic

The innervation and internal ultrastructure of the antennal flagellar sensilla of female Simulium arcticum (cytotypes IIL-3 and IIS-10.11) are described from transmission electron micrographs. Two types of contact chemosensilla and at least four types of olfactory sensilla (sensilla trichodea, two or more types of sensilla basiconica, grooved pegs) were found. These correspond to sensillar types previously described from scanning electron micrographs of the antennae of these species. In addition, possible thermo- and hygro-receptive sensilla coeloconica are described from the antennal tip. The sensory complement of the simuliid antenna is compared with those of certain other dipterans, and possible roles of these sensilla in host location and other behaviours are discussed.

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