Robbert De Iongh, Rafaela Perez, Mary Familari, Gemma Martinez, Frank J Lovicu, Gary Hime; Tob1 and Tob2 mark distinct RNA processing granules in differentiating lens fibre cells. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1722.
Purpose : Lens fibre cell differentiation involves a complex interplay of growth factor signals and tight control of gene expression via transcriptional and post-transcriptional regulators. Recent studies have demonstrated an important role for RNA-binding proteins, functioning in ribonucleoprotein granules, in regulating post-transcriptional expression during lens development. In this study we examined expression of Tob1 and Tob2, members of the BTG/Tob family of RNA-binding proteins, and examined the role of Tob1 in lens development.
Methods : Expression of Tob1 and Tob2 mRNA were detected by RT-PCR and in situ hybridisation and proteins were localized by double labelling immunofluorescence. The phenotype of Tob1-/- lenses was examined by histology and immunofluorescence for cell proliferation and differentiation markers.
Results : Tob1 and Tob2 mRNA were most intensely expressed in the early differentiating fibres, with weaker expression in the anterior epithelial cells and were down-regulated in the germinative zone of E15.5 lenses. Tob1 protein was detected from E11.5 to E16.5 and was predominantly detected in large cytoplasmic and occasional nuclear puncta in early differentiating fibre cells, often co-localising with the P-body marker, Dcp2. By contrast, Tob2 was detected in later differentiating fibre cells in the inner cortex, did not co-localise with Dcp2 and appeared to be present in polysomes. In vitro experiments using rat lens epithelial explants treated with or without a fibre differentiating dose of FGF2 showed that both Tob1 and Tob2 were up-regulated during FGF-induced differentiation. In differentiating explants, Tob1 also co-localised with Dcp2 in large cytoplasmic granules. Preliminary analysis of Tob1 mutants did not reveal a marked change in phenotype.
Conclusions : hese findings suggest that Tob proteins play distinct, but apparently non-essential roles in RNA processing during lens fibre differentiation.