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S. S. Saravanamuthu, Z. Liu, C. Y. Gao, C. J. Thiele, P. S. Zelenka; Castor Expression in Ocular Lens. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2794.
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Castor is a zinc finger transcription factor that controls cell fate within neuroblast cell lineages in Drosophila melanogaster and is upregulated in mammalian cell lines during differentiation associated with neurite extension and myotube formation. This study was undertaken to examine rat Castor (rCasz1) expression in the differentiating rat lens.
rCasz1 expression in isolated epithelia and fibers of post natal day 2 rat lenses was examined by immunoblotting and RT-PCR. Localization of rCasz1 expression was determined by immunofluorescence of frozen sections and whole mounted epithelia.
Immunofluorescence of the whole lens revealed expression in both epithelial and fiber cells, which was completely blocked by the antigenic peptide. Discrete nuclear localization of rCasz1 was evident in epithelial cells, consistent with its role as Zn-finger containing transcription factor. Immunofluorescence was more intense in the peripheral zone of the isolated epithelium than in the undifferentiated, central zone. Immunofluorescence in fiber cells was intense, but was primarily cytoplasmic. Immunoblotting of fiber cell proteins showed a single aproximately 20kDa immunoreactive band in the fiber cells that may represent a degradation product or a novel isoform. In contrast, immunoblotting of epithelial cell proteins showed 125kDa and 190kDa bands corresponding to two known human Castor (CASZ1) isoforms. The specificity of these immunoreactive bands was confirmed using the antigenic peptide. Semi-quantitative RT-PCR analysis showed a ten fold greater expression of rCasz1 transcripts in isolated epithelia than in fiber cells.
These data indicate that rCasz1 is expressed in lens and may be involved in the initiation of fiber cell differentiation in the transitional zone. This possibility is being examined in FGF-induced differentiation of rat epithelial explants.
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