Genomics


DNA SEQUENCING towards the third generation and beyond


Next-generation sequencing has expanded the frontiers of genomic research, opening up new avenues of enquiry and offering insights into diverse areas of biology. Rapid developments in this field are dramatically lowering costs and increasing speeds. With the arrival of third generation sequencing, this continually evolving technology is now being applied within clinical environments, where it has the potential to improve diagnosis and treatment outcomes of diseases such as cancer. There are still challenges facing sequencing today, in many ways magnified by the current economic climate, but these are being addressed by improvements across the sequencing ecosystem, but particularly in workflow, sequencing chemistry and analysis. Expected developments in sequencing technology, including the arrival of nanopore technology, offer the prospect of yet more advances in system performance and miniaturisation, going well beyond the present generation.


T


he genetic code is composed of the sequence of nucleotide bases which form the fundamental repetitive units of DNA. Deciphering the code – or the sequence of bases – offers insights into a vast repository of genetic information governing all manner of biological phenomena. This can be achieved by DNA sequencing. In recent years, sequencing via the con- ventional capillary-based Sanger method has been superseded by the advent of next-generation DNA sequencing technology, overcoming some of the limitations associated with the previous method. Next-generation DNA sequencing encompasses several technologies utilising distinct approaches to sequencing biochemistry. A defining feature of next-generation sequencing (NGS) is its ability to


Drug Discovery World Spring 2013


perform millions of sequencing reactions simulta- neously. This attribute is referred to as massively parallel sequencing.


Despite the diversity in sequencing biochemistry, most NGS approaches retain a high degree of sim- ilarity in the steps preceding sequencing and data acquisition. Initially, genomic DNA is randomly fragmented. Fragments are subsequently ligated to adapter sequences, facilitating formation of arrayed clusters of PCR-amplified DNA. Each spa- tially distinct array feature forms the location of one of millions of ongoing sequencing reactions. The DNA sequence is finally determined as a result of enzyme-driven synthesis of the nucleic acid chain, using the cluster fragments as a template. A signal released upon incorporation of a specific


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By Andrew Szopa-Comley


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