Pax2 overexpression and regulation studies in vertebrate eye
Abstract
Pax2 is a member of the Paired Bo x family of transcription factors and plays a pivotal role in eye, ear, spinal cord and kidney development. Loss-of-Pax2 expression has been linked with various developmental and functional abnormalities such as coloboma in the eye and Wilm's tumor in the kidney. In the following studies we attempted to analyze the role of Pax2 in the eye and mechanism of regulation by SHH and BMP7. Pax2 loss-of-expression has been associated with lack of choroid fissure closure, referred to as a Coloboma. Coloboma also results from downregulation of genes like Shh and Vax. In this study we determined that the ectopic Pax2 expression the in ventral optic cup phenocopies loss of Pax2 expression. The underlying mechanism of coloboma formation is very different in Pax2 overexpression as compared to the Pax2 loss-of-expression. In this study, Pax2 overexpression lead to a cell fate change from retinal and retinal pigmented epithelium cells (RPE) to glial cells. The presence of ectopic astrocytes and their processes interfere with the choroid fissure, leading to a coloboma whereas in Pax2 loss-of-expression, the basal laminae that separate the two opposing lips of choroid fissure fails to break, leading to a defect in choroid fissure closure. In addition to coloboma formation, we determined that Pax2 overexpression in RPE leads to secondary neural retina formation adjacent to the Pax2-electroporated region and that the ectopic retina overexpresses Fgf8. In this study, we also analyzed the regulation of Pax2 by SHH and BMP7 in astrocytes derived from retina. BMP7 and SHH have been shown to regulate Pax2 but the mechanism is not understood. We determined that BMP7 and SHH activate both PAX2 and phospho-PAX2 in retinal derived astrocytes. In addition, SHH acts upstream of BMP7 and, BMP7 and SHH decrease the binding of TLX (a repressor of Pax2) on the Pax2 promoter. Furthermore, phospho-SMAD1 and GLI2, the downstream targets of BMP7 and SHH signaling respectively, directly interact with TLX. Together this data reveals a new mechanism for the synergistic actions of signaling pathways in retinal cell determination and differentiation and suggest interactions of regulatory pathways that are applicable to other developmental programs.
Degree
Ph.D.
Advisors
Belecky-Adams, Purdue University.
Subject Area
Molecular biology|Neurosciences|Cellular biology
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