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Jian Zou, Xiangyun Wei; The Roles Of Crb Proteins During Neurulation And Early Retinal Morphogenesis In Zebrafish. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6018.
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Many epithelium-derived tissues express the Crumbs (Crb) polarity proteins, which form complexes with other polarity proteins such as Nok and Lin7 to maintain epithelial polarity and regulate tissue morphogenesis. Several crb genes have been identified in zebrafish. However their functional difference during neuroepithelial morphogenesis remains unclear. This study was undertaken to investigate the roles of Crb1, Crb2a, and Crb2b in neurulation and early retinal morphogenesis in zebrafish.
Specific antibodies against Crb1, Crb2a, and Crb2b were generated and used to analyze the expression patterns of Crb proteins in the neuroepithelium by immunohistochemistry. Morpholinos were used to analyze the loss-of-function phenotypes of the crb genes. Pulldown assays and mammalian cell culture assays were performed to determine the physical adhesion porperties of the extracellular domains of Crb proteins. The crb mRNAs were injected into 1-4-cell stage embryos for rescue or overexpression assays.
Crb1, Crb2a and Crb2b are expressed in distinct and yet overlapping temporal and spatial patterns earlier in the neural tube, as well as later in the developing brain, retina, and the spinal cord. For example, Crb2a is the only Crb protein expressed in undifferentiated retinal neuroepithelium. The results of biochemical pull-down and HEK293 cell culture expression assays suggested that Crb proteins play redundant roles in the neuroepithelium by mediating cell-cell adhesion at the apical surface. The severity of the disruption of epithelial polarity is correlated with the total Crb protein level in the neuroepithelium.
The authors demonstrated that the novel adhesion function mediated by the Crb proteins and their intracellular partners play an important role during neurulation and early retinal morphogenesis. The temporal and spatial regulation of Crb-mediated cell-cell adhesion may regulate the balance between tissue plasticity and rigidity. This regulation might underlie dynamic tissue morphogenesis, which requires the tissue to bear a certain amount of plasticity to accommodate shape and position changes of individual cells as well as intercellular cohesiveness to maintain tissue integrity and architecture.
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