Investigation of RNA Granules in Lens Development

The mammalian lens is an avascular tissue that refracts and focuses light onto the retina. It consists of a monolayer of epithelial cells located anteriorly, and differentiated fiber cells that make up the bulk of the tissue. In early lens development, cells at the anterior of the lens vesicle form the lens epithelium while cells in the posterior form primary fiber cells. In later stages, lens epithelial cells near the equatorial region of the cells exit the cell cycle and differentiate into secondary fiber cells that elongate and undergo organelle degradation, which is necessary for lens transparency. Loss of lens transparency is called the eye disease cataract, the leading cause of blindness worldwide. Defects in embryonic development that affect lens epithelial cell maintenance or fiber differentiation can result in pediatric cataract. Because epithelial to fiber differentiation occurs throughout life, even mild alterations to this process over time can impact the onset of age‐related cataract. Therefore, understanding the molecular mechanism of lens development and fiber cell differentiation is necessary to develop non‐surgical alternative therapeutic interventions for cataract. Because, differentiating fiber cells involve degradation of nuclei, and progress toward compromised transcriptional potential, it is hypothesized that various post‐transcriptional mechanisms of gene expression control may have evolved to regulate this process. Recently, RNA‐binding proteins (RBPs) and RNA granule (RGs) components have been implicated as important mediators of post‐transcriptional gene control regulation in the lens, deficiency of which causes cataract in human and/or different animal models. In particular, mutations or reduced dosage of the Tudor family protein TDRD7 (Tudor domain containing protein 7) cause cataract in human, mouse and chicken. Tdrd7 protein forms RNA granules (Tdrd7‐RGs) that co‐localize with another conserved RBP and RG component called Stau1 (Staufen1), which also forms ribonucleoprotein particles (Stau1‐RNPs) in the lens. This co‐localization was observed in primary fiber cell differentiation, particularly at the elongating apical and basal regions. Stau1‐RNPs are known to function in the localization and decay of target mRNA transcripts in different cell types ranging from Drosophila oocytes to mammalian neurons. However, Stau1's function in the lens remains uncharacterized. We hypothesized that Tdrd7‐RGs and Stau1‐RNPs may function in the localization of key lens transcripts in differentiating fiber cells. As an initial step toward addressing this hypothesis, we characterized in detail the expression of Tdrd7 protein in different stages of mouse lens development. Using immunofluorescence, we find that in addition to primary fiber cells, Tdrd7 and Stau1 co‐localize in secondary lens fiber cells. Further, we are developing transgenic mouse models with lens‐specific expression of Tdrd7‐GFP and Stau1‐mCherry fusion proteins directed under the Alpha A Crystallin (Cryaa) promoter. This transgenic model will inform on the real‐time spatiotemporal dynamics between Tdrd7‐RGs and Stau1‐RNPs via live imaging, and in turn, serve to elucidate their function in lens development. Support or Funding Information 2017 Delaware Governor's Bioscience Fellowship, NEI/NIH RO1 EY021505 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .