Further mutation in this enhancer of the third-site to a 2 n spacer, as in D. virilis, restored the levels of expression similar to the original SLF4 enhancer (Fig 4C).
Comparative genomics combined with TF database analysis were used in order to identify potential TF for the enhancer activity of the first intron of MIF.
The sev gene promoter without the sev enhancer showed very weak promoter activity in S2 cells (data not shown) and the sev enhancer located in the second intron of the sev gene is known to be required for eye disc-specific expression (Basler and Hafen 1988).
Recently, we have shown [ 5] that in cases where we have a biological model with an experimentally verified map of enhancer elements, the second problem can be tackled with a probabilistic model giving high accuracy of predictions of both target genes and their tissue-specific expression.
A 57 bp cis-regulatory element named E1E (exon 1 enhancer) in the first exon of PAX6 plays an important role in the expression of this gene in glioblastoma cell lines (23), and a powerful silencer (SX250) located between 1518 and 1268 bp from the A of the ATG codon is able to repress the promoter activity of PAX6 in cervical carcinoma and glioblastoma cell lines (22).
On the other hand, insertion of the EGFP reporter cassette after the PK2 promoter might nullify a potential enhancer in the first intron of PK2 gene.
As well, others have identified a TCR-responsive enhancer in the first intron of the FOXP3 gene that is dependent upon a cyclic AMP response element binding protein/activating transcription factor site [51].
Using an unbiased DNase I hypersensitivity approach, we have identified a novel cell type-specific enhancer within the first intron of MIF.
Thus, the effects of BMP signaling on Müller glial gene expression, at least for Rlbp1, might function directly through pSmad1/5/8 binding to an enhancer in the first intron of the Rlbp1 gene.
Since the discovery of the SV40 enhancer, the first enhancer shown to regulate transcription of a mammalian gene [1], enhancers have been defined as DNA sequence regions that can up-regulate transcription independent of position and orientation with respect to the gene.
These findings are consistent with those of Ragvin et al. who have recently identified long range enhancers within the first intron of FTO that influence the expression of IRX3, located ∼470 kb downstream of this region.
