FIGURE 2.

Structural alterations induced by heterozygous knock-in of the catalytically inactive Gpx4-mutant Sec46Ala. A, sperm extracted from the epididymal cauda were stained according to the Spermac® method (see “Materials and Methods”) and classified into three different groups according to morphological appearance of their midpiece in light microscopy. a, Grade 1 sperm: no granulation in the midpiece (normal sperm); b, Grade 2 sperm: moderate granulation in the midpiece; c, Grade 3 sperm: severe granulation in the midpiece. B, electron microscopy of grade 1 (a) and grade 3 (b) sperm. Grade 1 sperm are characterized by condensed mitochondria and a lack of intramitochondrial vacuoles and regular mitochondrial capsules. Grade 3 sperm have swollen mitochondria with intramitochondrial vacuoles and disturbed structure of the mitochondrial capsule. C, immunogold staining of different parts of epididymal cauda sperm indicating the intracellular localization of Gpx4 in the head (a and b), the midpiece (c and d), and the cytoplasmic droplet (e and f). Immunopositive material is indicated by the small black dots. U46A represents Sec46Ala exchange.