A genetic time-delay circuitry in mammalian cells.

Gene expression circuitries with time-delayed expression profiles regulate key events, such as oscillating systems, noise elimination, and coordinated multi-step processes, in all organisms from bacteria to mammalian cells. We present the rational synthesis of a genetic circuit displaying time-delayed expression in silico and in mammalian cells. The network is based on a time-delay circuit, where the tetracycline-responsive transactivator (tTA) induces expression of the pristinamycin-responsive repressor PIP-KRAB, which silences expression of the terminal human placental secreted alkaline phosphatase (SEAP). While the addition of pristinamycin I inactivates PIP-KRAB and results in the immediate resumption of SEAP expression, addition of tetracycline abolishes PIP-KRAB synthesis. Consequently, SEAP production remains repressed until the PIP-KRAB buffer in the cell is eliminated. We characterized in silico and in vivo the time-delayed expression properties and analyzed the impact of the size and stability of the PIP-KRAB buffer on fine-tuning of the response kinetics. This tunable time-delay circuitry represents a biologic building block for emulating a fundamental circuit topology in integrated artificial synthetic gene networks for the design of tailor-made cell types and organisms. (c) 2007 Wiley Periodicals, Inc.