Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): PASKIN is an orphan receptor PAS sensory protein containing a serine/threonine kinase domain. In situ hybridization (upper right) and targeted integration of a beta-galactosidase reporter gene revealed strong PASKIN expression during spermatogenesis in the mouse testis. The lower left picture shows whole-mount X-Gal staining of the testes of Paskin^+/+, Paskin^+/-, and Paskin^-/- littermate mice. (See related article on p. 6780.)