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N. Tanimoto, D. Chen, R. Bremner, M. W. Seeliger; Retinal Function in Cell-Specific Neuronal Differentiation Mutants of the Retinoblastoma Protein (RB)-Pathway. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3840.
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The retinoblastoma protein (Rb), besides its role as a tumor suppressor, is critical for the cell cycle exit during birth of post-mitotic retinal transition cells (RTCs). In addition, Rb promotes RTC differentiation into neuronal cells by inhibition of E2f transcription factors, which otherwise cause apoptosis of theses cells. The purpose of this study was to investigate the functional integrity of cell-specific neuronal differentiation mutants.
Since Rb loss has a number of systemic effects, the retinal consequences were studied in a tissue-specific Cre-lox system (Chen et al., Cancer Cell 2004; 5:539-551). For this work, Rb mutants, E2f1 knockouts, E2f1/Rb double mutants, and functionally normal wild-type mice were examined with Ganzfeld electroretinography (ERG; Multiliner Vision, VIASYS, Germany) under both scotopic and photopic conditions. The study was performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.
Retinal Rb-deficient mutants did show only rudimentary ERG responses. This is due to the fact that E2f1 is not repressed in the absence of Rb, leading to apoptosis of about half the rods, most bipolar cells and most ganglion cells. The ERG was not completely flat due to a minor area at the posterior pole lacking Cre expression. In contrast, the ERG of E2f1 knockouts was practically normal, and that of the E2f1/Rb double mutants was only marginally reduced (low-normal). Thus, rod/bipolar survival and function are severely affected in the absence of Rb, but are restored when E2f1 is also removed. Interestingly, although Rb null starburst amacrine cells are abnormal, which is due to a cell cycle-independent effect of E2f3a, this defect did not cause clearly identifiable alterations of the ERG.
This study underlines the value of electrophysiological investigations of genetically modified mouse models in the assessment of the functional impact of developmental processes in the retina.
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