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Hardeep Singh, Xiaoliang Xu, David Cobrinik; Co-expression of RNAs Corresponding to Multiple Retinal Cell Markers in Human Cone Precursors. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3728.
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Retinoblastoma cells were previously shown to express numerous cone photoreceptor markers, to depend upon cone-specific signaling circuitry, and to lack established protein markers of other retinal cell types (Xu et al., 2009). These findings implied that retinoblastoma cells have a cone-dominant phenotype consistent with a cone precursor tumor origin. However, a recent study showed that individual retinoblastoma cells express markers of multiple retinal cell types at the RNA level, suggestive of a progenitor/neuronal hybrid cell phenotype (McEvoy et al, 2011). To assess whether the hybrid RNA expression pattern of retinoblastoma cells is compatible with cone precursor features, the present study tested whether individual cone precursors express RNAs that were ostensibly specific to other retinal cells.
Human fetal week 19 retinal cells were stained for CD133, which has modest expression in retinal progenitor cells and hi-level expression in photoreceptors. Medium size CD133hi cells were isolated by FACS and either stained for cone markers (CRX and cone arrestin) or used for cDNA synthesis and amplification. Single cell expression of progenitor cell markers (SFRP2, LHX2), amacrine/horizontal/ganglion cell markers (PAX6, SYT1, NEFM, CALB1) and photoreceptor markers (L/M opsin, ARR3, TRB2, NRL) was tested using qPCR and agarose gel electrophoresis.
91.2% of FACS sorted CD133hi medium size cells were double immuno-positive for cone arrestin and CRX. These cells did not show immuno-reactivity with other retinal cell types. Three CD133+ medium size cells show co-expression of progenitor, amacrine/horizontal/ganglion, and photoreceptor markers. Cell-1 co-expressed progenitor markers (SFRP2, LHX2), an amacrine/horizontal/ganglion cell marker (NEFM), and photoreceptor markers (ARR3 and NRL). Cell-2 co-expressed progenitor (NEFM) and photoreceptor marker (ARR3). Cell-3 co-expressed progenitor markers (SFRP2, LHX2), an amacrine/horizontal/ganglion marker (CALB1), and photoreceptor markers (L/M opsin, ARR3).
Like retinoblastoma cells, normal human cone precursors co-express diverse yet ostensibly cell type-specific markers at the RNA level. Co-expression of these mRNAs may be a vestigial feature of cone photoreceptor development that is reflected in retinoblastoma cell biology.
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