Classification of the Seminiferous Epithelial Cycle in the Sika Deer (Cervus nippon)

The sika deer (Cervus nippon) is the only Cervidae inhabiting Japan, except a feral foreign cervid, the Reeves’ muntjac (Muntiacus reevesi). The sika deer is short-day seasonal breeder, and its rut occurs from October to December (Suzuki et al. 1992). When considering the biology of seasonal breeders, it is especially important to elucidate testicular functions during seasonal testicular changes. In the mature testes of the roe deer during the breeding season, the composition of the seminiferous epithelium periodically changes throughout spermatogenesis (Blottner et al. 1996). Many studies on the stages of the epithelial cycle have been reported in experimental and domestic animals (Foote et al. 1972; Swierstra et al. 1974; Berndtson 1977; Ekstedt et al. 1986; Pawar and Wrobel 1991). For example, the seminiferous epithelial cycle is divided into 14 stages in the rat (Leblond and Clermont 1952) and 8 stages in the bull (Wrobel and Schimmel 1989). Information about these stages is essential for morphological and functional researches on the testes and provides the basis of understanding testicular regulatory mechanisms (Toppari et al. 1986; Zhu et al. 1997; Zhou et al. 2002; Schon et al. 2004; Klonisch et al. 2006). In the rat, the morphological changes of the Sertoli cells with each seminiferous epithelial stage are concerned with the control of phosphorylation of the cytoskeletal protein, vimentin (Zhu et al. 1997). In the mouse, androgen receptors in the Sertoli cells show stage-dependent expression with the most intense expression in stages VI–VII (Zhou et al. 2002). Histological studies on postnatal testicular development and seasonal changes of the testes have been reported in the sika deer (Yamauchi et al. 1982). Structural changes of the seminiferous tubules, plasma and fecal testosterone levels and localization of steroidogenic enzymes have already been examined with annual testicular changes of the sika deer (Suzuki et al. 1992; Yamauchi et al. 1997; Kameyama et al. 2002; Hayakawa et al. 2004). However, the stages of the seminiferous epithelial cycle are not yet fully defined in the sika deer, although they have been reported in other cervids, the fallow deer (Wrobel et al. 1993) and roe deer (Schon et al. 2004). In the present study, therefore, we categorized the seminiferous epithelial stages in the sika deer.