  Recently, a large number of studies have been carried out on the early
signatures of sudden regime shifts in systems as diverse as ecosystems,
financial markets, population biology and complex diseases. Signatures of
regime shifts in gene expression dynamics are less systematically investigated.
In this paper, we consider sudden regime shifts in the gene expression dynamics
described by a fold-bifurcation model involving bistability and hysteresis. We
consider two alternative models, Models 1 and 2, of competence development in
the bacterial population B. subtilis and determine some early signatures of the
regime shifts between competence and noncompetence. We use both deterministic
and stochastic formalisms for the purpose of our study. The early signatures
studied include the critical slowing down as a transition point is approached,
rising variance and the lag-1 autocorrelation function, skewness and a ratio of
two mean first passage times. Some of the signatures could provide the
experimental basis for distinguishing between bistability and excitability as
the correct mechanism for the development of competence.
