Animal receptors ― Examples of cellular signal perception molecules

Considerable information has accumulated about the mechanisms by which animal cells perceive extracellular signals. In sharp contrast, very little is known about cellular signal perception in plant cells. The purpose of this article is to examine signal perception mechanisms in animal cells and to highlight general principles that may prove applicable to the study of plant systems. I will focus on the receptors in target cells that specifically bind the signal molecule(s). This is the initial event in the signal cascade that eventually leads to changes in cellular metabolism (e.g., gene expression) in targeted cells. Secondary messengers, which are often involved in the signal transduction process subsequent to the binding of signal molecules to receptors, are the focus of another review (see article by C. A. West, this volume).