A mutation in the silver gene leads to defects in melanosome biogenesis and alterations in the visual system in the zebrafish mutant fading vision.
Forward genetic screens have been instrumental in defining molecular components of visual function. The zebrafish mutant fading vision (fdv) has been identified in such a screen due to defects in vision accompanied by hypopigmentation in the retinal pigment epithelium (RPE) and body melanocytes. The RPE forms the outer most layer of the retina, and its function is essential for vision. In fdv mutant larvae, the outer segments of photoreceptors are strongly reduced in length or absent due to defects in RPE cells. Ultrastructural analysis of RPE cells reveals dramatic cellular changes such as an absence of microvilli and vesicular inclusions. The retinoid profile is altered as judged by biochemical analysis, arguing for a partial block in visual pigment regeneration. Surprisingly, homozygous fdv vision mutants survive to adulthood and show, despite a persistence of the hypopigmentation, a partial recovery of retinal morphology. By positional cloning and subsequent morpholino knock-down, we identified a mutation in the silver gene as the molecular defect underlying the fdv phenotype. The Silver protein is required for intralumenal fibril formation in melanosomes by amylogenic cleavage. Our data reveal an unexpected link between melanosome biogenesis and the visual system, undetectable in cell culture.
Schonthaler
Helia B
HB
Swiss Federal Institute of Technology, Department of Biology, and Brain Research Institute of the University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Lampert
Johanna M
JM
von Lintig
Johannes
J
Schwarz
Heinz
H
Geisler
Robert
R
Neuhauss
Stephan C F
SC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002875:Chromosomes; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D008040:Genetic Linkage; D005819:Genetic Markers; D016678:Genome; D006720:Homozygote; D008544:Melanocytes / Q000648:ultrastructure; D020460:Melanosomes / Q000502:physiology* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D020419:Photoreceptor Cells, Vertebrate / Q000648:ultrastructure; D010857:Pigment Epithelium of Eye / Q000648:ultrastructure; D017354:Point Mutation; D011110:Polymorphism, Genetic; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021101:Radiation Hybrid Mapping; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D014785:Vision, Ocular / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology / Q000235:genetics* / Q000502:physiology; D029961:Zebrafish Proteins / Q000737:chemistry / Q000235:genetics*
D005819:Genetic Markers; D021382:Protein Sorting Signals; D029961:Zebrafish Proteins