Hox transcription factors may play a role in regulating segmental function of the adult epididymis.

Spermatozoa entering the epididymis do not exhibit progressive motility and are incapable of fertilizing an egg in vivo. They undergo maturation through a series of cellular events occurring primarily in the proximal epididymis and are stored as mature sperm in the distal epididymis (Hinton and Palladino, 1995; Turner, 1995). The epididymis consists of a single, highly convoluted duct packed within a tunica albuginea capsule, and the organ is conventionally divided from proximal-to-distal epididymis into the caput, corpus, and cauda regions. The different regions can be distinguished by their morphology (Robaire and Hermo, 1988) as well as by their different patterns of gene and protein expression (Cornwall and Hann, 1995; Kirchhoff, 1999). These regionalized patterns may reflect specific epididymal functions that are crucial for sperm maturation and storage, and studies to understand their regulation have been extensive. Presently, it is believed that the complex interplay between regional differences in androgen levels (Turner et al, 1984), activity of steroid metabolizing enzymes (Robaire and Viger, 1995; Orgebin-Crist, 1996), signaling via tyrosine kinase receptors (Sonnenberg-Riethmacher et al, 1996), and presentation of lumicrine signaling molecules (Hinton et al, 1998) is responsible for region-specific gene expression and protein synthesis. In this context, it has become evident that gene or protein expression often occurs coincidentally with infraregional segmentation of the epididymal tubule, as opposed