Building Synthetic Cells─From the Technology Infrastructure to Cellular Entities

Abstract

The de novo construction of a living organism is a compelling vision. Despite the astonishing technologies developed to modify living cells, building a functioning cell "from scratch" has yet to be accomplished. The pursuit of this goal alone has─and will─yield scientific insights affecting fields as diverse as cell biology, biotechnology, medicine, and astrobiology. Multiple approaches have aimed to create biochemical systems manifesting common characteristics of life, such as compartmentalization, metabolism, and replication and the derived features, evolution, responsiveness to stimuli, and directed movement. Significant achievements in synthesizing each of these criteria have been made, individually and in limited combinations. Here, we review these efforts, distinguish different approaches, and highlight bottlenecks in the current research. We look ahead at what work remains to be accomplished and propose a "roadmap" with key milestones to achieve the vision of building cells from molecular parts.

Figure 1

Our working definition of living systems, based on Tibor Gánti’s Chemoton model of life. Compartmentalization, replication, and metabolism together make up minimal criteria for a living system. From these other features emerge, including evolution, responsiveness to stimuli, and directed movement.

Figure 2

Four different molecular platforms for studying life. Outgoing from externally provided template DNA (1), a cell-free transcription/translation (Tx/Tl) system uses complex substrates and a chemical energy-donor (2) to synthesize RNA, proteins and potentially other biocatalytically (enzymatically) formed products (3). An encapsulated cell-free system is often a liposome enclosing a cell-free Tx/Tl system. A synthetic cell would function more like a natural cell in that it could be a self-sustaining system that is capable of replication.

Figure 3

Major approaches to building a synthetic cell: bottom-up (a), top-down (b), and middle-out (c) are distinguished as the basic concepts of currently ongoing research. Top-down approaches generally seek to find a “minimal genome” of an existing organism, while the bottom-up approach aspires to de novo create a cell “from scratch” or based on macromolecules. Middle-out approaches utilize modules of known function (e.g., organelles, extracts) to assemble a new cell or major elements/mechanisms thereof.

Figure 4

Milestones toward the de novo design and construction of a synthetic cell. Many of these steps can be performed in parallel with a mixing and matching approach to integration.