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From the Department of Ophthalmology, University of Washington School of Medicine, Seattle.
PURPOSE. Angiogenesis refers to the latter stage of vascular development. It has been reported that angiopoietin-like factor cornea-derived transcript 6 (CDT6) encodes a protein homologous to angiopoietins that could play a critical role in blocking a receptor of angiopoietin (Tie2) and therefore contribute to the avascularity and transparency of the cornea in the developing embryo and the adult. This study was focused on isolation and characterization of the CDT6 promoter.
METHODS. Rapid amplification of cDNA ends (5'-RACE) was used to isolate the CDT6 promoter from an adaptor-ligated genomic DNA fragment library and to identify the transcription initiation site of the CDT6 gene. The RNase protection assay was performed to confirm the initiation site. The sequence similarity, binding sites for putative transcription factors, and transcriptional activity of human and mouse CDT6 promoters were compared. Corneal and noncorneal cells from humans and other animals were transiently transfected with CDT6 promoter-chloramphenicol acetyltransferase (CAT) reporter constructs to analyze the transcriptional activity of the promoter.
RESULTS. A 2956-bp human CDT6 promoter fragment and a 3142-bp
mouse CDT6 promoter fragment were isolated. The major
transcription initiation sites of the human and mouse
CDT6 genes were located at 224 and 168 bp, respectively,
upstream of the translation initiation site. Human and mouse
CDT6 promoter sequences were very similar. Both
promoters were minus TATA and CAAT boxes close to the transcription
initiation site. Transfection into human corneal and noncorneal cells
and into nonhuman cells revealed that the human CDT6
promoter probably contains positive and negative
cis-regulatory elements that modulate cell, tissue, and
species specificity. The human CDT6 promoter contains
four interferon (IFN)-stimulated response elements (ISREs). No ISREs
could be identified in the mouse promoter. IFN-
stimulated
transcriptional activity of the human promoter.
CONCLUSIONS. The human and mouse CDT6 promoters have similar
sequences and share many cis-regulatory elements.
IFN-
appears to have an important role in regulating transcription
of the human, but not the mouse, CDT6
promoter.
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