Fig. 3

Oocytes from cultured fetal ovaries progress through prophase I of meiosis in the presence or absence of etoposide. Fetal ovaries cultured for 2, 4 or 6 days were stained for Sycp3 in order to assess the synaptonemal complex (SC). Oocytes were categorised into leptotene/zygotene, (SC assembling but not fully formed) by the presence of extensive networks of fine Sycp3 threads, often with large nuclear aggregates of Sycp3 that has not yet assembled into SC (Ai); pachytene, (fully synapsed SC) by the presence of a thicker well-spaced long Sycp3 threads (Aii); or diplotene, (SC disassembling but still present) by the presence of short thick fragments of Sycp3 threads (Aiii). B: Meiotic progression was examined in germ cells from control ovaries and from ovaries exposed to 150 ng ml⁻¹ etoposide during culture. Control oocytes progressed through the early stages of prophase I in a normal manner during the first 6 days of culture, with the majority at leptotene/zygotene at Day 2 of culture, pachytene at Day 4 and diplotene by Day 6 of culture, immediately prior to follicle formation. Oocytes exposed to 150 ng ml⁻¹ etoposide during culture were able to progress through to diplotene. At Day 2 of culture only, oocytes from etoposide-treated ovaries were at more advanced meiotic stages than those from control ovaries, but there was no difference at Days 4 or 6. Scale bars: 10 μm, n = 961 control oocytes and n = 994 treatment oocytes. Stars denote significant difference between oocytes from etoposide-exposed ovaries (lower panel) relative to controls (upper panel; **p < 0.01)