ABSTRACT
Multicellular organisms require specific intercellular communication to properly organize the complex body plan during embryogenesis and maintain the physiological properties and functions during the entire life span. While growth factors, neurotransmitters and peptide hormones bind to membrane receptors thereby inducing the activity of intracellular kinase cascades or the JAK-STAT/Smad signaling pathways, other small hydrophobic signaling molecules such as steroid hormones, certain vitamins and metabolic intermediates enter the target cells and bind to cognate members of a large family of nuclear receptors. Nuclear receptors are of major importance for intercellular signaling in the animal, as they converge different intra- and extracellular signals on the regulation of genetic programs. They are transcription factors that, in addition to regulating cognate gene programs:
respond directly through physical association with a large variety of hormonal and metabolic signals;
integrate diverse signaling pathways as they themselves are targets of post-translational modifications;
regulate the activities of other major signaling cascades (commonly referred to as ‘signal transduction crosstalk’).
