Site-specific mRNA cleavage for selective and quantitative profiling of alternative splicing with label-free optical biosensors.

Alternative Splicing of messenger RNA precursors is a key process in gene regulation, contributing to the diversity of proteomes by the alternative selection of exonic sequences. Most cancers are associated with alterations in this mechanism, enhancing their proliferation and survival, and can be employed as cancer biomarkers. Label-free optical biosensors are ideal tools for the highly sensitive and label-free analysis of nucleic acids. However, their application for alternative splicing analysis has been hampered due to the formation of complex and intricate long-range base-pairing interactions which make the direct detection in mRNA isoforms difficult. To solve this bottleneck, we introduce a methodology for the generation of length-controlled RNA fragments from purified total RNA, which can be easily detected by the biosensor. The methodology seizes RNase H enzyme activity to degrade the upstream and downstream RNA segments flanking the target sequence upon hybridization to specific DNA-oligos. It allows the fast and direct monitoring of Fas gene alternative splicing in real-time employing a Surface Plasmon Resonance (SPR) biosensor. We demonstrate the selective and specific detection of mRNA fragments in the pM-nM concentration range, reducing quantification errors and showing 81% accuracy when compared to RT-qPCR. The site-specific cleavage outperformed a random RNA hydrolysis by increasing the detection accuracy in 20%, making this methodology particularly appropriate for label-free quantification of alternative splicing events in complex samples.