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Dean Bok

Bio: Dean Bok is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Photoreceptor outer segment. The author has an hindex of 1, co-authored 1 publications receiving 1138 citations.

Papers
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Journal ArticleDOI
TL;DR: The disposal phase of the retinal rod outer segment renewal process has been studied by radioautography in adult frogs injected with tritiated amino acids to identify inclusions within the pigment epithelium by virtue of their content of radioactivity.
Abstract: The disposal phase of the retinal rod outer segment renewal process has been studied by radioautography in adult frogs injected with tritiated amino acids. Shortly after injection, newly formed radioactive protein is incorporated into disc membranes which are assembled at the base of the rod outer segment. During the following 2 months, these labeled discs are progressively displaced along the outer segment owing to the repeated formation of newer discs. When the labeled membranes reach the end of the outer segment, they are detached from it. They subsequently may be identified in inclusion bodies within the pigment epithelium by virtue of their content of radioactivity. These inclusions have been termed phagosomes. Disc membrane formation is a continuous process, but the detachment of groups of discs occurs intermittently. The detached outer segment fragments become deformed, compacted, undergo chemical changes, and are displaced within the pigment epithelium. Ultimately, the material contained in the phagosomes is eliminated from the cell. In this manner the pigment epithelium participates actively in the disposal phase of the rod outer segment renewal process.

1,180 citations


Cited by
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Journal ArticleDOI
TL;DR: This review summarizes the current knowledge of RPE functions and describes how failure of these functions causes loss of visual function.
Abstract: Located between vessels of the choriocapillaris and light-sensitive outer segments of the photoreceptors, the retinal pigment epithelium (RPE) closely interacts with photoreceptors in the maintenance of visual function. Increasing knowledge of the multiple functions performed by the RPE improved the understanding of many diseases leading to blindness. This review summarizes the current knowledge of RPE functions and describes how failure of these functions causes loss of visual function. Mutations in genes that are expressed in the RPE can lead to photoreceptor degeneration. On the other hand, mutations in genes expressed in photoreceptors can lead to degenerations of the RPE. Thus both tissues can be regarded as a functional unit where both interacting partners depend on each other.

2,387 citations

Book ChapterDOI
01 Jan 1981
TL;DR: This paper used pyramidal neurons and neuroglial cells in the primary auditory cortex (area 41) of the aging rat as a basis for the following account, and referred to recent studies of their own colleagues and of other investigators as appropriate within that context.
Abstract: It is not the intent of this chapter to provide a comprehensive documentation of all the changes that have been recorded in the cells of the central nervous system as they age. Rather, we have chosen to follow the rather narrow path of using our own studies of the pyramidal neurons and neuroglial cells in the primary auditory cortex (area 41) of the aging rat as a basis for the following account, and to refer to recent studies of our own colleagues and of other investigators as appropriate within that context. This approach is bound to result in a rather biased description of the aging of neurons and neuroglia, but we believe that sufficient information will be given in this account for the reader to use it as a means of gaining access to studies that provide additional information and other views.

925 citations

Journal ArticleDOI
TL;DR: The results provide genetic evidence for an essential role of a receptor tyrosine kinase in a specialized form of phagocytosis and suggest a molecular model for ingestion of outer segments by RPE cells.
Abstract: Vertebrate photoreceptor cells are the basic sensory apparatus of the retina, capable of converting the energy of absorbed photons into neuronal signals. The proximal portions of mammalian photoreceptor outer segments are synthesized daily by cell bodies, and outer segment tips are shed with a circadian rhythm, resulting in a complete turnover of outer segments about every 9 days. The shed outer segments are phagocytosed by adjacent retinal pigment epithelial (RPE) cells, and metabolites are recycled to photoreceptors. The Royal College of Surgeons (RCS) rat is a widely studied, classic model of recessively inherited retinal degeneration in which the RPE fails to phagocytose shed outer segments, and photoreceptor cells subsequently die. We have used a positional cloning approach to study the rdy (retinal dystrophy) locus of the RCS rat. Within a 0.3 cM genetic inclusion interval, we have discovered a small deletion of RCS DNA that disrupts the gene encoding the receptor tyrosine kinase Mertk. The deletion includes the splice acceptor site upstream of the second coding exon of Mertk and results in a shortened transcript that lacks this exon. The aberrant transcript joins the first and third coding exons, leading to a frameshift and a translation termination signal 20 codons after the AUG. The concordance of these and other data indicate that Mertk is probably the gene for rdy. Our results provide genetic evidence for an essential role of a receptor tyrosine kinase in a specialized form of phagocytosis and suggest a molecular model for ingestion of outer segments by RPE cells.

872 citations

Journal ArticleDOI
TL;DR: Although its importance was previously unrecognized, TAM signalling promises to have an increasingly prominent role in studies of innate immune regulation.
Abstract: Recent studies have revealed that the TAM receptor protein tyrosine kinases — TYRO3, AXL and MER — have pivotal roles in innate immunity. They inhibit inflammation in dendritic cells and macrophages, promote the phagocytosis of apoptotic cells and membranous organelles, and stimulate the maturation of natural killer cells. Each of these phenomena may depend on a cooperative interaction between TAM receptor and cytokine receptor signalling systems. Although its importance was previously unrecognized, TAM signalling promises to have an increasingly prominent role in studies of innate immune regulation.

717 citations

Journal ArticleDOI
03 Dec 1976-Science
TL;DR: When albino rats are reared in cyclic light, a burst of rod outer segment disk shedding occurs in the retina soon after the onset of light, and the subsequent degradation of large phagosomes to smaller structures within pigment epithelial cells proceeds rapidly.
Abstract: When albino rats are reared in cyclic light, a burst of rod outer segment disk shedding occurs in the retina soon after the onset of light. The number of large packets of outer segment disks (phagosomes) in the pigment epithelium at this time is 2.5 to 5 times greater than at any other time of day or night. The subsequent degradation of large phagosomes to smaller structures within pigment epithelial cells proceeds rapidly. The burst of disk shedding follows a circadian rhythm for at least 3 days, since it occurs in continuous darkness at the same time without the onset of light.

692 citations