The comparison of doses measured by radiochromic films and semiconductor detector in a 175 MeV proton beam

We wanted to verify the response of radiochromic films in a 175 MeV clinical proton beam used at the Joint Institute for Nuclear Research in Dubna against doses measured using semiconductor detectors and compare the results with published data from other centres. Radiochromic films (RCFs) MD-55 and a Vidar VXR-16 scanner were used. The films were irradiated in an unmodulated proton beam and with a beam modulated with a bolus and a ridge filter. Obtained dose distributions were compared with dose distributions measured with a Si-semiconductor detector.For the unmodulated beam the difference between the RCF and the semiconductor detector was 12% in the Bragg peak top. For the modulated beam the difference inside the spread-out Bragg peak region was 4%. Observed deviations between doses measured with RCF and Si-detector outside the Bragg peak were caused by the inhomogeneity of radiochromic emulsion. In the Bragg peak region the RCF doses were lower than those measured by semiconductors. The results were in agreement with published data from other proton therapy centres.     

Lens Transplantation in Zebrafish and its Application in the Analysis of Eye Mutants

The lens plays an important role in the development of the optic cup^[1,2]. Using the zebrafish as a model organism, questions regarding lens development can be addressed. The zebrafish is useful for genetic studies due to several advantageous characteristics, including small size, high fecundity, short lifecycle, and ease of care. Lens development occurs rapidly in zebrafish. By 72 hpf, the zebrafish lens is functionally mature ^[3]. Abundant genetic and molecular resources are available to support research in zebrafish. In addition, the similarity of the zebrafish eye to those of other vertebrates provides basis for its use as an excellent animal model of human defects^[4-7]. Several zebrafish mutants exhibit lens abnormalities, including high levels of cell death, which in some cases leads to a complete degeneration of lens tissues ^[8]. To determine whether lens abnormalities are due to intrinsic causes or to defective interactions with the surrounding tissues, transplantation of a mutant lens into a wild-type eye is performed. Using fire-polished metal needles, mutant or wild-type lenses are carefully dissected from the donor animal, and transferred into the host. To distinguish wild-type and mutant tissues, a transgenic line is used as the donor. This line expresses membrane-bound GFP in all tissues, including the lens. This transplantation technique is an essential tool in the studies of zebrafish lens mutants.Open in a separate windowClick here to view.^{(64M, flv)}     

Zebrafish N-cadherin,encoded by the glass onion locus,plays an essential role in retinal patterning

Genetic screens in zebrafish identified several loci that play essential roles in the patterning of retinal architecture. Here, we show that one of them, glass onion, encodes the N-cadherin gene. The glo(m117) mutant allele contains a substitution of the Trp2 residue known for its essential role in the adhesive properties of classic cadherins. Both the glo(m117) and pac(tm101b) mutant N-cadherin alleles affect the polarity of the retinal neuroepithelial sheet and, unexpectedly, both result in cell-nonautonomous phenotypes in retinal patterning. The late onset of mutant N-cadherin phenotypes may be due to the ability of classic cadherins to substitute each other's function.     

Characterization of a white bass (Morone chrysops) embryonic cell line with epithelial features

The genus Morone is an important one for U.S. aquaculture, but there has been no available cell line from this genus. We report here a cell line (the WBE line) derived from white bass embryos that has been grown for more than 80 passages over 21 mo in Dulbecco modified Eagle medium supplemented with fetal bovine serum. The WBE line showed epithelial features with positive immunohistochemical staining for cytokeratin and intercellular junctions when observed by electron microscopy. The doubling time, transformation characteristics, response to cryopreservation, and karyotype were determined. The WBE line was also tested by polymerase chain reaction to verify the species of origin and to screen for mycoplasma infection. This epithelial cell line may prove useful for the study of host-pathogen interactions that occur at the epithelial surface in this commercially important fish species.     

Functional conservation of atonal and Math1 in the CNS and PNS

To determine the extent to which atonal and its mouse homolog Math1 exhibit functional conservation, we inserted (beta)-galactosidase (lacZ) into the Math1 locus and analyzed its expression, evaluated consequences of loss of Math1 function, and expressed Math1 in atonal mutant flies. lacZ under the control of Math1 regulatory elements duplicated the previously known expression pattern of Math1 in the CNS (i.e., the neural tube, dorsal spinal cord, brainstem, and cerebellar external granule neurons) but also revealed new sites of expression: PNS mechanoreceptors (inner ear hair cells and Merkel cells) and articular chondrocytes. Expressing Math1 induced ectopic chordotonal organs (CHOs) in wild-type flies and partially rescued CHO loss in atonal mutant embryos. These data demonstrate that both the mouse and fly homologs encode lineage identity information and, more interestingly, that some of the cells dependent on this information serve similar mechanoreceptor functions.     

Mutations that affect the survival of selected amacrine cell subpopulations define a new class of genetic defects in the vertebrate retina

Amacrine neurons are among the most diverse cell classes in the vertebrate retina. To gain insight into mechanisms vital to the production and survival of amacrine cell types, we investigated a group of mutations in three zebrafish loci: kleks (kle), chiorny (chy), and bergmann (bgm). Mutants of all three genes display a severe loss of selected amacrine cell subpopulations. The numbers of GABA-expressing amacrine interneurons are sharply reduced in all three mutants, while cell loss in other amacrine cell subpopulations varies and some cells are not affected at all. To investigate how amacrine cell loss affects retinal function, we performed electroretinograms on mutant animals. While the kle mutation mostly influences the function of the inner nuclear layer, unexpectedly the chy mutant phenotype also involves a loss of photoreceptor cell activity. The precise ration and arrangement of amacrine cell subpopulations suggest that cell-cell interactions are involved in the differentiation of this cell class. To test whether defects of such interactions may be, at least in part, responsible for mutant phenotypes, we performed mosaic analysis and demonstrated that the loss of parvalbumin-positive amacrine cells in chy mutants is due to extrinsic (cell-nonautonomous) causes. The phenotype of another amacrine cell subpopulation, the GABA-positive cells, does not display a clear cell-nonautonomy in chy animals. These results indicate that environmental factors, possibly interactions among different subpopulations of amacrine neurons, are involved in the development of the amacrine cell class.     

oko meduzy mutations affect neuronal patterning in the zebrafish retina and reveal cell-cell interactions of the retinal neuroepithelial sheet

Mutations of the oko meduzy (ome) locus cause drastic neuronal patterning defect in the zebrafish retina. The precise, stratified appearance of the wild-type retina is absent in the mutants. Despite the lack of lamination, at least seven retinal cell types differentiate in oko meduzy. The ome phenotype is already expressed in the retinal neuroepithelium affecting morphology of the neuroepithelial cells. Our experiments indicate that previously unknown cell-cell interactions are involved in development of the retinal neuroepithelial sheet. In genetically mosaic animals, cell-cell interactions are sufficient to rescue the phenotype of oko meduzy retinal neuroepithelial cells. These cell-cell interactions may play a critical role in the patterning events that lead to differentiation of distinct neuronal laminae in the vertebrate retina.     

Isolation of a novel visual-system-specific arrestin: an in vivo substrate for light-dependent phosphorylation

Absorption of a photon of light by rhodopsin triggers mechanisms responsible for excitation as well as regulation of the phototransduction cascade. Arrestins are a family of proteins that appear to be responsible for terminating the active state of G-protein-coupled receptors. One of the major substrates of light-dependent phosphorylation in the visual cascade of Drosophila was purified and partially sequenced. The complete primary structure of the protein was determined by isolating the corresponding gene, which revealed it to be a new isoform of arrestin, Arr2. Arr2 is 401 residues in length, and shares 47% sequence identity with the Drosophila Arr1 protein and 42% with human arrestin. We show that the two Drosophila arrestin genes are differentially regulated, and that Arr2 is a specific substrate for a calcium-dependent protein kinase. This is the first demonstration of in vivo regulation of arrestins in a transduction cascade, and provides a new level of modulation in the function of G-protein-coupled receptors.