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(Investigative Ophthalmology and Visual Science. 2008;49:1542-1552.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-1300
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Dual Roles for Prox1 in the Regulation of the Chicken βB1-Crystallin Promoter

Xiaoren Chen,1,2 Jennifer R. Taube,1,2 Vladimir I. Simirskii,1 Tapan P. Patel,1 and Melinda K. Duncan1

1From the Department of Biological Sciences, University of Delaware, Newark, Delaware.

PURPOSE. Lens fiber cell differentiation is marked by the onset of βB1-crystallin expression and is controlled by the cooperative action of a set of transcription factors including Prox1, an atypical homeodomain protein. Previously, the authors reported that Prox1 directly interacts with the OL2 element found in the chicken βB1-crystallin basal promoter to activate the expression of this gene. Here they mapped the location of activating and repressing sequences of the full-length chicken βB1-crystallin promoter (–432/+30) in lens epithelial cells, annular pad cells, and intact lens and characterized Prox1-binding sites found in this region.

METHODS. Transfection analysis and transgenic mice were used to characterize upstream regions of the chicken βB1-crystallin gene. DNaseI footprinting and chromatin immunoprecipitation was performed to identify Prox1-binding sites, and transfection analyses were used to characterize these sites functionally.

RESULTS. Sequences between –152 and –432 of the chicken βB1-crystallin promoter mediated either promoter activation or repression, depending on the stage of lens differentiation tested. Two new Prox1-binding sites were found in this region that bound Prox1 more avidly than the OL2 element. However, neither binding site conferred Prox1-mediated activation on a heterologous promoter; instead, each allowed Prox1 to repress promoter function.

CONCLUSIONS. The function of the upstream region of the chicken βB1-crystallin promoter changes depending on cellular context. These data suggest that Prox1 function as a transcriptional activator could be regulated at the DNA level based on the characteristics of the responsive elements.






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Copyright © 2008 by the Association for Research in Vision and Ophthalmology