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Zahra Motahari, Andrea Sophia Viczian, Michael Ezra Zuber; Tbx3 is required at neural plate stages for normal eye formation in Xenopus laevis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6404.
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Vertebrate eye formation begins in the anterior neural plate in a region called the eye field. Seven transcription factors called the eye field transcription factors or EFTFs (Tbx3, Rax, Pax6, Nr2e1, Six3, Lhx2, and Six6) are expressed in a dynamic and overlapping pattern in the eye field. Functional inactivation of any one of the EFTFs results in animals (humans, mice, frogs, and/or fish) with abnormal or no eyes. Tbx3 can regulate the expression of other EFTFs and is implicated in the dorsoventral patterning of the retina at optic vesicle stages. However its role at earlier, neural plate stages has not been extensively investigated.
In situ hybridization and RTPCR were used to determine the expression pattern and timing of the tbx3a and tbx3b homeologs in X. laevis. Injection of tbx3 RNA and Tbx3 morpholinos were used to misexpress and knockdown tbx3 during neural plate stages. Hormone inducible fusion constructs consisting of Tbx3 and the human glucocorticoid receptor were used to determine when Tbx3 functions during embryogenesis.
Both homeologs of tbx3 (tbx3a & tbx3b) are expressed in the eye field in a pattern consistent with a role in eye field and eye formation. Using mosaic analysis, we found that Tbx3 was sufficient to convert pluripotent cells to a retinal lineage. Conversely, knockdown of tbx3 translation resulted in abnormal eye formation in vivo. Blocking translation of both tbx3a and tbx3b was required to inhibit normal eye formation. Furthermore, donor eye fields from Tbx3 morpholino injected embryos fail to form retina when transplanted to host embryo eye fields.
These results support the conclusion that Tbx3 is required for normal eye field formation. The precise cellular and molecular mechanisms by which Tbx3 regulates early eye formation is currently under investigation.
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