Optimization of long-range PCR protocol to prepare filaggrin exon 3 libraries for PacBio long-read sequencing

BackgroundThe filaggrin (FLG) protein, encoded by the FLG gene, is an intermediate filament-associated protein that plays a crucial role in the terminal stages of human epidermal differentiation. Loss-of-function mutations in the FLG exon 3 have been associated with skin diseases. The identification of causative mutations is challenging, due to the high sequence homology within its exon 3 (12,753 bp), which includes 10 to 12 filaggrin tandem repeats. With this study we aimed to obtain the whole FLG exon 3 sequence through PacBio technology, once 13-kb amplicons have been generated.Methods and resultsFor the preparation of SMRTbell libraries to be sequenced using PacBio technology, we focused on optimizing a 2-step long-range PCR protocol to generate 13-kb amplicons covering the whole FLG exon 3 sequence. The performance of three long-range DNA polymerases was assessed in an attempt to improve the PCR conditions required for the enzymes to function properly. We focused on optimization of the input template DNA concentration and thermocycling parameters to correctly amplify the entire FLG exon 3 sequence, minimizing non-specific amplification.ConclusionsTaken together, our findings suggested that the PrimeSTAR protocol is suitable for producing the amplicons of the 13-kb FLG whole exon 3 to prepare SMRTbell libraries. We suggest that sequencing the generated amplicons may be useful for identifying LoF variants that are causative of the patients' disorders.

Automated summary

In this study, the whole sequence of FLG exon 3 was obtained using PacBio technology to investigate its association with skin diseases. A 2-step long-range PCR protocol was optimized to generate 13-kb amplicons covering the entire FLG exon 3 sequence. The PrimeSTAR protocol was found to be suitable for generating amplicons, and sequencing them may aid in identifying causative variants of the patients' disorders.