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S. A. Lachke, F. Alkuraya, I. Saadi, R. Cavallesco, S. Choe, A. Tsai, A. Drack, R. L. Maas; Identification of a Novel Cataract Gene, TDRD7, a Component of Lens RNA Granules That Regulates Fiber Cell Differentiation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3477.
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© ARVO (1962-2015); The Authors (2016-present)
We have generated a tool to efficiently identify genes that play key roles in lens biology and cataractogenesis. We demonstrate its utility by identifying a novel cataract gene, TDRD7, which has led to the discovery of lens cytoplasmic RNA granules and their role in post-transcriptional regulation in fiber cell differentiation.
Using whole genome transcript profiling by microarray, we generated a developmental profile of the mouse lens transcriptome as it transitions from the stage of placode invagination to that of vesicle formation. We established a normalization protocol that ranks probe datasets based on their lens enrichment p-values, allowing detection of genes essential in lens development and disease.
We studied a juvenile cataract patient who carries the balanced paracentric inversion 46, XY, inv(9)(q22.33q34.11). The database predicted TDRD7 as the most probable candidate among 50 genes within a 5 Mb interval around the q22.33 breakpoint. TDRD7 disruption and haploinsufficiency in patient lymphoblastoid cells was confirmed by FISH and Western blot analysis. TDRD7 expression was highly specific in differentiating lens fiber cells and was conserved between chick and mice. In chick, TDRD7 knockdown in lenses resulted in cataract formation recapitulating the patient phenotype. In mice, Tdrd7 protein localized to cytoplasmic RNA granules in differentiating lens fiber cells. We found that lens cells harbored two classes of RNA granules namely, Processing (P)-bodies, which contain components of the microRNA machinery and regulate mRNA turnover, and Stau1 RNA granules that are involved in mRNA transport. Tdrd7 granules differentially co-localized with both classes of RNA granules, and were mechanistically distinct from P-bodies as indicated by their resistance to cycloheximide. We hypothesized that TDRD7 haploinsufficiency alters the intricate interplay between these RNA granules resulting in misregulation of lens transcripts. Consistent with this model, Tdrd7-knockdown in lens-derived cells specifically led to aberrant transcript levels of Foxe3 and Prox1, two genes with key roles in lens development.
We report a unique lens gene expression database that served as an efficient tool to identify a novel cataract gene, TDRD7. We demonstrate TDRD7 to be a component of cytoplasmic RNA granules that interacts with P-bodies and Stau1 transport granules to regulate post-transcriptional events in differentiating lens fiber cells in turn, assigning a role for RNA granules in organogenesis.
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