A bistable genetic switch based on designable DNA-binding domains

An analytical approach to bistable biological circuit discrimination using real algebraic geometry

“…A second MBN of particular interest, herein referred to as the monomerdimer (MD) toggle, is a double-negative switch variant in which one of the repressors functions as a monomer (figure 1a, bottom). While to the best of our knowledge no MD toggle circuit has been constructed, the components necessary for its implementation exist in the form of monomeric singlechain transcriptional repressor proteins [17], as well as in transcription-activator-like effectors (TALEs) and CRISPR/Cas nucleases that have been engineered as repressors [18,19]. Other exotic toggle-like circuit topologies have also been proposed and/or built [13,18,[20][21][22].…”

“…In a recent study [18], it was shown that a toggle variant consisting of two monomeric repressors derived from TALE protein DNA-binding domains cannot support bistability, but that the introduction of positive feedback in the form of two TALE-based activators that compete with the repressors for promoter access makes the system bistable. However, as we show below, it is not necessary to have two symmetric positive feedback loops for bistability; a single activator added to the monomeric toggle is sufficient.…”

“…While to the best of our knowledge no MD toggle circuit has been constructed, the components necessary for its implementation exist in the form of monomeric singlechain transcriptional repressor proteins [17], as well as in transcription-activator-like effectors (TALEs) and CRISPR/Cas nucleases that have been engineered as repressors [18,19]. Other exotic toggle-like circuit topologies have also been proposed and/or built [13,18,[20][21][22]. An understanding of the differences in how these various toggles perform can be beneficial, in particular for those circuits that have yet to be built and for which a priori knowledge of their behaviour could aid in their development.…”

“…However, as we show below, it is not necessary to have two symmetric positive feedback loops for bistability; a single activator added to the monomeric toggle is sufficient. We begin by combining components from the 'mutual repressor' and 'competitive feedback' models of Lebar et al [18], so that the two types of promoters-one containing a single binding site for both an activator and a repressor, and a second that is only responsive to a repressor-are present in one hybrid circuit:…”

Genome-Editing Technologies: Principles and Applications

“…Facilitated by many of the insights gained from zinc-finger transcription factor technology, both TALEs and CRISPR-Cas9 have now further expanded the possibilities of engineered transcriptional activators and repressors. For example, TALEs and CRISPR-Cas9 have enabled rapid construction of custom genetic circuits and logic gates (Gaber et al 2014;Lebar et al 2014;Liu et al 2014b), complex gene regulation networks (Nielsen and Voigt 2014;Nissim et al 2014), and even facilitated cellular reprogramming (Gao et al 2013) and the differentiation of mouse embryonic fibroblasts to skeletal myocytes (Chakraborty et al 2014). dCas9 transcriptional effectors have even been used to efficiently mediate repression and activation of endogenous genes in Drosophila (Lin et al 2015b) and in plant cells (Piatek et al 2015).…”