Delta-like 4 mRNA is regulated by adjacent natural antisense transcripts

Keguo Li, Tamjid Chowdhury, Padmanabhan Vakeel, Christopher Koceja, Venkatesh Sampath, Ramani Ramchandran

Recent evidence suggests that a majority of RNAs in the genome do not code for proteins. They are located in the sense (S) or antisense (AS) orientation and, to date, the functional significance of these non-coding RNAs (ncRNAs) is poorly understood. Here, we examined the relationship between S and AS transcripts in the regulation of a key angiogenesis gene, Delta-like 4 (Dll4). Rapid Amplification of cDNA Ends (RACE) method was used to identify natural antisense transcripts in the Dll4 gene locus in murine and human endothelial cells, referred to as Dll4 Anti-Sense (Dll4-AS). Messenger RNA (mRNA) levels of Dll4 and Dll4-AS were quantified by real-time PCR. The function of Dll4-AS was investigated by overexpression and knocking down of Dll4-AS. Dll4-AS comprises of three isoforms that map proximal to the Dll4 promoter region. Expression patterns of Dll4-AS isoforms vary among different endothelial cell lines, but are always congruent with those of Dll4. A dual promoter element in the Dll4 locus has been identified that controls the expression of both transcripts. Both Dll4-AS and Dll4 are sensitive to cellular density in that higher cellular density favors their expression. Exogenous Dll4 stimuli such as VEGF, FGF and Notch signaling inhibitor altered both DLL4-AS and DLL4 expression suggesting co-regulation of the transcripts. Also, knocking down of Dll4-AS results in down-regulation of Dll4 expression. As a consequence, endothelial cell proliferation and migration increases in vitro, and sprout formation increases. The regulation of Dll4 by Dll4-AS was also conserved in vivo. A novel form of non-coding RNA-mediated regulation at the Dll4 locus contributes to vascular developmental processes such as cell proliferation, migration and sprouting.