Neuropeptides and Peptide Hormones

Abstract

Several types of chemical messengers are employed by the nervous system for local or more diffuse signaling. Among these the peptides are the most diverse in structure and function. In nervous tissues they are typically produced by neurons or neurosecretory cells, and can therefore be specified as neuropeptides or peptide hormones, respectively. Additionally, many peptides are produced by endocrine cells or other cell types in different locations. In fact, the same peptide can be expressed by all these cell types in a given animal. Neuropeptides and peptide hormones are ubiquitous in the nervous and endocrine systems of all metazoans. Not only do these peptides exist in a large number of distinct molecular forms, they are also very diverse in their actions and signaling mechanisms. Thus, in a single animal species there may be more than a 100 different neuropeptides and peptide hormones (and their receptors), and each can have multiple functions. The peptides are encoded in the genome as parts of larger precursor proteins, referred to as prepropeptides. This direct coding means that when whole animal genomes have been sequenced the total inventory of neuropeptides and peptide hormones can be predicted. Such sequence data can also be used for analysis of neuropeptide evolution and show that some peptide sequences are well conserved across a broad range of species, whereas others display considerable variability and some are even unique to certain taxa. In this chapter we show that in some cases not only peptide sequences, but also the receptor structures and mechanisms of action and physiological functions can be conserved from invertebrates to vertebrates.