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W.-L. Wang; ASC-2 is Important for Lens Fiber Cells Survival and Not Involved in Retinal Signaling for Fiber Cells Differentiation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2782.
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© ARVO (1962-2015); The Authors (2016-present)
ASC-2 (Activating Signal Cointegrator-2), a recently identified coactivator, functions in mediating the transcriptional activity of nuclear receptors (NRs) and other transcription factors. Its interaction with NRs is mediated through the LXXLL motif, nuclear receptor box (NR box). A fragment harboring the N-terminal NR box, DN1, ubiquitously expressed in mice acting via a dominant negative (DN) mechanism caused a plethora of phenotypes, including micropthalmia, posterior lenticonus and cataract (Kim et al., 2002). The recruitment of ASC-2 to retinoic acid (RA) receptor-β was hampered as shown in cell culture based assays. Since RA signaling is important for lens development, studies of ASC-2 in the lens can provide novel insight into lens development and differentiation.
Immunohistochemistry was performed to determine ASC-2 expression in the eye. To study the lens specific function of ASC-2, we expressed the DN1 fragment in the lens using the αA-Crystallin promoter (-367~+46). H&E staining was performed to compare the phenotypes. DAPI staining and TUNEL assay were conducted to analyze apoptosis in the lens. To link phenotypes caused by DN1 with disrupted lens signaling pathways, total RNA prepared from E15.5 wild type and transgenic mice lenses were used for RNA microarray and quantitative RT-PCR analysis.
Two transgenic lines were established and morphological studies identified similar phenotypes in the lens. Some of these defects such as micropthalmia and lens opacity are similar to the published model described above. In contrast, our model does not form the posterior lenticonus. Additional defects observed in our model include disturbed ASC-2 expression, incomplete denucleation, retarded growth, migration and differentiation of lens fiber cells. These defects are caused by an internal expression of the DN1 fragment and not by its expression in the surrounding ocular tissues. In microarray analysis, we found ~600 genes up or down-regulated in the transgenic samples including genes downstream of RA signaling pathway, c-fos and p21waf1/cip1. No change in αA- and αB-Crystallin expression was detected in the lens.
The current data suggest that the lower expression of the crystallin genes expression caused by ubiquitous expression of ASC-2 DN1 fragment results from defects outside of the lens. The candidate genes whose expression is under ASC-2 DN1 influence are c-fos, p21waf1/cip1, Ccng1, Ddit3, Atf3, Klf5, Ap2α, Prox1, and Bfsp.
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