SINGLE-CELL SEQUENCING: UNRAVELING GENETIC HETEROGENEITY

Abstract

Cellular heterogeneity is a fundamental characteristic of multicellular organisms as well as some models of artificial intelligence. It contributes to the normal development of tissue variety and functional stability. However, in the context of disease, cellular homogeneity is often disrupted, resulting in genomic, epigenomic, transcriptomic, and phenotypic diversity among individual cells in a population. This genomic and phenotypic diversity is the driving force behind tumorigenesis, metastasis, drug resistance, and treatment failure in many cancers (Ye et al., 2016). Currently, the bulk population assay remains the gold standard in characterizing genomic and phenotypic diversity. However, population-based experiments can only provide averaged information and fail to represent the entire spectrum of cellular states. As a consequence, an understanding of oncogenic cellular diversity and the ability to accurately predict and intercept cancer progression are beyond reach. Whole-genome amplification (WGA) was first demonstrated in 1992 using degenerate oligonucleotide-primed PCR (DOP-PCR) on a few nanograms of input DNA. During the late 1990s, several other WGA protocols were developed, some of which are still in use today. Scheduling the polymerase chain reaction (PCR) and isothermal amplification at various temperatures can minimize bias due to local differences in GC content. In general, PCR-based WGA methods are simple, rapid, and inexpensive. Isothermal amplification is becoming increasingly popular, particularly for low-input DNA (C. Macaulay & Voet, 2014).