  Genetic regulatory networks enable cells to respond to the changes in
internal and external conditions by dynamically coordinating their gene
expression profiles. Our ability to make quantitative measurements in these
biochemical circuits has deepened our understanding of what kinds of
computations genetic regulatory networks can perform and with what reliability.
These advances have motivated researchers to look for connections between the
architecture and function of genetic regulatory networks. Transmitting
information between network's inputs and its outputs has been proposed as one
such possible measure of function, relevant in certain biological contexts.
Here we summarize recent developments in the application of information theory
to gene regulatory networks. We first review basic concepts in information
theory necessary to understand recent work. We then discuss the functional
complexity of gene regulation which arrises from the molecular nature of the
regulatory interactions. We end by reviewing some experiments supporting the
view that genetic networks responsible for early development of multicellular
organisms might be maximizing transmitted 'positional' information.
