Characterization of arterial endothelium specific promoter/enhancer region in mouse Alk1 gene

Arterial endothelial cells (ECs) are potentially invaluable targets in gene therapies for various disorders. Aiming at restricting curative gene expression in arterial ECs, we previously isolated a 9.2 kb arterial regulatory fragment from mouse activin receptor‐like kinase 1 (ALK1) gene, which stretches from 2.7 kb upstream of exon 1 to the middle of intron 3. In addition, we showed that the intron 2 region is required for the endogenous Alk1 expression and may contain enhancer element(s). Intriguingly, both the promoter region and intron 2 of mouse Alk1 gene contains several blocks of sequences that are highly homologous to the human corresponding regions. In order to further characterize this unique arterial EC regulatory region and to shorten this regulatory fragment for the use in viral vectors, after the removal of non‐conserved sequences, we were able to generate a new transgenic construct that carries only the sequences conserved between human and mouse as a regulatory unit. Preliminary analyses were conducted on the offspring of the first founder mouse and they revealed that in addition to some ectopic expressions, this chimeric fragment is sufficient to drive transgene expression in arterial ECs. The ectopic expressions may be triggered by some regulatory elements close to the transgene integration site that are exercising influence on the transgene expressions. Alternatively, it is possible that the non‐conserved sequences may contain silencer elements or may act as a spacer between the promoter and enhancer. Further characterization of offspring from the following founders as well as human ALK1 expression pattern should help identify the vital regulatory elements in this valuable regulatory fragment.