12 h suggesting that increased water movement across the Sertoli cell membrane may contribute to increased tubular diameter and testis weight. The absence of spermatogenic progression over the time-course studied is likely to reﬂect the inactive state of the Sertoli cell in the adult hpg testis and the time required for the Sertoli cell to become active enough to support germ cell maturation. Real-time PCR studies of a small number of known germ cell genes showed that there was a variable response of germ cell transcripts to FSH stimulation. POU5F1 has been shown to be necessary for primordial germ cell survival (Kehler et al. 2004) and the increase in response to FSH, albeit small, may facilitate an increase in spermatogonial number within the testis. DKKL1 and ZFP541 are expressed in both spermatocytes and spermatids (Kohn et al. 2005, Choi et al. 2008) while HDC and SPATIAL are associated with round spermatids and the later stages of sperma- togenesis (Saﬁna et al. 2002, Irla et al. 2003). Lack of a general increase in germ cell transcripts (data from both arrays and real-time PCR) would indicate that the effects seen are not due to an overall increase in germ cell number but are more likely to be part of an early speciﬁc response to FSH stimulation. It has been shown previously that more prolonged treatment of hpg mice with FSH will stimulate an increase in germ cell number and development (O’Shaughnessy et al. 1992, Singh & Handelsman 1996b, Baines et al. 2008) but the stimulatory effect of FSH on the Leydig cells makes interpretation of the FSH effects on the germ cells difﬁcult because of the known stimulatory effect of testosterone on germ cell development in the hpg mouse (O’Shaughnessy & Shefﬁeld 1990, Singh et al. 1995). In this study, FSH treatment of hpg mice for up to 72 h induced signiﬁcant changes in Sertoli cell transcript levels and led to indirect stimulation of Leydig cell function. The changes in Leydig cell activity probably induced further changes in androgen-depen- dent Sertoli cell transcripts. While FSH is known to be required for optimal germ cell development (Abel et al. 2000, 2008), treatment of hpg mice for 72 h did not have a marked effect on germ cell differentiation suggesting that longer-term action of FSH is required to induce germ cell proliferation and progression. Declaration of interest The authors declare that there is no conﬂict of interest that could be perceived as prejudicing the impartiality of the research reported. Funding This study was supported by the Wellcome Trust (grant number 078137). www.endocrinology-journals.org Effects of FSH on testicular transcript levels . 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