Reproduction Abstracts

Introduction: Onset timing of meiosis is different between the two sexes in mammals. In the mouse, meiosis in the ovary initiates during late stages of the second trimester, whereas germ cells in the testis at the same stage enter mitotic arrest and do not initiate meiosis until postpartum. In the present study, I have studied effects of ovarian steroids on the formation of synaptonemal complex in the neonatal mouse testis.

Materials and methods: Testis was collected aseptically from neonatal C57BL/6N mice, de-capsulated, placed atop an agarose block placed in wells of multi-well plates, and then cultured with control medium containing fetal bovine serum, transferrin and insulin, and either with or without steroid hormones. After culture for a few weeks, testis was recovered and assayed for SYCP1 and its transcripts, by immunofluorescence (IF) and qRT-PCR respectively.

Results and discussion: SYCP1-specific IF signals were detected in the testis from days 6–8 postpartum that was cultured for 1 week or longer with no addition of steroids, whereas specific signals with reduced intensities were detected in the testis that was cultured with progesterone. Estradiol β added alone showed no or little effects but an additive effect with progesterone in suppression of SYCP1. QRT-PCR confirmed that progesterone reduced the amount of Sycp1-specific transcripts, and that estradiol β further reduced when added with progesterone. Removal of these steroids from culture medium induced the resumption of SYCP1 expression. These results indicate that ovarian steroid hormones are likely to be candidates for physiological suppressors of meiosis in the testis.