Microspread oocytes from fetal mouse ovaries, demonstrating different appearances of axial elements and labelling for cleaved PARP-1 and TUNEL during meiotic prophase I. Red = COR1 immunodetection indicating the axial elements of oocyte chromosomes, used to determine the stage of meiotic prophase I. Blue = Cleaved PARP-1 immunodetection. Presence of cleaved PARP-1 indicates inability to repair DNA damage, indicative of apoptosis. Green = TUNEL labelling. Indicates presence of DNA double strand breaks. A. Oocyte in late zygotene with intact axial elements shown by COR1 staining in red. This oocytes was negative for both cleaved PARP-1 and TUNEL. B and C. Oocyte at pachytene showing discontinuities in COR1 staining. This oocyte was TUNEL positive (green) and negative for cleaved PARP-1. D. Oocyte in pachytene with intact axial elements, negative for both cleaved PARP-1 and TUNEL. E and F. Oocyte in early diplotene showing discontinuities in COR1 staining. This oocyte was positive for cleaved PARP-1 (blue) and negative for TUNEL. G, H and I. Oocyte with short sections of dense discontinuous COR1 staining, possibly degenerating diplotene stage. This oocyte stained positive for both TUNEL (H) and cleaved PARP-1 (I), indicating advanced apoptosis. J. Two adjacent oocytes stained for COR1, demonstrating clear differences in nuclear size. Oocytes showing limited expansion, such as that on the right, we have termed 'compressed'. Both of these oocytes were TUNEL negative (shown green) and PARP-1 positive (not shown).