eGFP-CircRNA incorporates the eGFP sequence and is synthesized through in vitro transcription and cyclization. After transfection into cells, eGFP-CircRNA expresses enhanced green fluorescent protein (eGFP) within the cells. This wild-type protein (GFP) was first isolated in 1962 by Osamu Shimomura from the jellyfish Aequorea victoria. GFP possesses unique luminescent properties, being independent of any cofactors or substrates and requiring only molecular oxygen. Therefore, GFP is often fused with the gene of the target protein to monitor the expression or localization of the target protein. However, GFP has notable limitations in applications. To address these shortcomings, molecular biologists developed variants of GFP called eGFP, which share the same secondary structure as GFP. Importantly, the codon sequence of eGFP has been optimized to be better suited for expression in mammalian cells.