Figure 1.

Cellular signalling pathways and gene expression regulation. A: In 1969, RJ Britten and EH Davidson hypothesized a theoretical model consisting of five ‘genes’ – sensor (S), integrator (I), activator (A) RNA, receptor (R), and producer (P). A ‘battery’ comprises of various P and its regulators that are activated by a single S in response to a cellular cue. For example, Battery 1 targets producer genes (P) ‘a’ and ‘b’, based on the signal provided by sensor gene (S) ‘1’. The five gene-components work co-ordinately to activate various batteries of genes involved in specific biological processes (refer to Table 1). The five ‘gene’ types are listed in the figure key. The goal of these components is to effect gene expression upon stimulation from certain environmental cues. Integration of cellular signals and regulatory sites can be performed at the level of the Integrator (I), or Receptor (R). B: Cellular signalling networks as found in eukaryotes. The complexity of this system enables effective transmission of signals from the environment to the gene-level to deploy various gene expression programs in the cell. Here, the binding of a receptor at the surface of the cell, triggers the activation of a cascade of signalling proteins, which in turn activate various transcriptional regulatory factors. The active transcriptional regulatory factors bind at specific genes and regulating the gene’s expression, in response to the external stimulus.