Emerging and evolving concepts in gene essentiality

A gene is considered essential if it is required for the reproductive success of a cell or an organism. Gene essentiality is a core concept of genetics, with repercussions in evolutionary, systems and synthetic biology and with applications in drug development.The 'essentialome' is defined as the complete set of genes that are individually essential in a given organism. Recent genome sequencing and editing technologies are enabling the identification of essentialomes in a progressively larger number of non-model organisms and higher eukaryotes.The essentiality of many genes is dependent on the environment and/or genetic context and can be altered in the course of both short-term and long-term evolutionary processes. Hence it is not an absolute and static property of a gene.There seems to be a gradient of gene essentiality among genes in each genome, with some essential genes being more prone to losing their essentiality than others. Hence essentiality is not a binary but a quantitative property of a gene.The context-dependent nature of gene essentiality can be exploited to develop more effective or more specific antimicrobials and provides avenues for patient-tailored anticancer therapies.The evolvable nature of gene essentiality has implications for drug target prioritization: genes that are less likely to lose their essentiality should be associated with a lower incidence of resistance when targeted by a drug.