Gene therapy is a promising approach to the treatment of various inherited diseases, but its development is complicated by a number of limitations of the natural promoters used. The currently used strong ubiquitous natural promoters do not allow for the specificity of expression, while natural tissue-specific promoters have lowactivity. These limitations of natural promoters can be addressed by creating new synthetic promoters that achieve high levels of tissue-specific target gene expression. This review discusses recent advances in the development of synthetic promoters that provide a more precise regulation of gene expression. Approaches to the design of synthetic promoters are reviewed, including manual design and bioinformatic methods using machine learning. Examples of successful applications of synthetic promoters in the therapy of hereditary diseases and cancer are presented, as well as prospects for their clinical use.

The untranslated regions (UTRs) of messenger RNAs (mRNAs) play a crucial role in regulating translational efficiency, stability, and tissue-specific expression. The review describes various applications and challenges of UTR design in the development of gene therapy and mRNA-based therapeutics. UTRs affect critical biological functions, such as mRNA stability, modulation of protein synthesis, and attenuation of immune response. Incorporating tissue-specific microRNA (miRNA)-binding sites into 3′ UTRs might improve precise targeting of transgene expression and minimize off-target effects. Nucleotide modifications (pseudouridine, N1-methyladenosine, and N4-acetylcytidine) in mRNA and UTRs in particular, improve mRNA stability and translational efficiency. At the same time, several challenges remain, such as lack of consensus on UTRs best suited for certain biomedical applications. Current efforts are focused on integrating high-throughput screening, computational modeling, and experimental validation to refine UTR-based therapeutic strategies. The review presents current information on the design of UTRs and their role in therapeutic applications, with special focus on the possibilities and limitations of existing approaches.