DROSOPHILA bHLH-PAS DEVELOPMENTAL REGULATORY PROTEINS

1. INTRODUCTION Drosophila bHLH-PAS proteins play important roles in development and physiology. They can be divided into three groups: (i) Tgo and its bHLH-PAS dimerization partners, (ii) circadian rhythms, and (iii) hormone function. The Tgo dimerization group carries-out many developmental roles, and includes: Dysfusion (Dys), Similar (Sima), Single-minded (Sim), Spineless (Ss), and Trachealess (Trh). They are the subject of this chapter (the other Drosophila PAS genes are reviewed in the chapters by Hogenesch and Kay, Montell, and Wilson). Members of the Tgo dimerization group share a number of common features. Foremost, they form DNA-binding heterodimers with Tgo. They are well-conserved between nematodes, insects, and mammals. Each carries-out multiple developmental roles, and some have roles as master regulators of tissue formation. The tissues, cell types, and biological processes whose development and function are influenced by bHLH-PAS proteins are diverse. There is little redundancy or overlap of function, although, there is one example of a bHLH-PAS protein regulating levels of another.