Fig. 5. Spermiogenesis abnormalities in RIM-BP3 knockout mice revealed by transmission electron microscopy. (A,B) Step 5 spermatids. Unfused proacrosomal vesicles are aligned above the bent acroplaxome in a mutant round spermatid (B). The ends of the extending acroplaxome in this section are marked with white arrows. (C,D) Step 9 spermatids. Acrosome fragmentation was occasionally observed in mutant elongating spermatids as shown in D. The breakage point is indicated with an arrowhead (D, inset). (E-G) Step 10/11 spermatids. At this elongating stage, abnormalities ranged from acrosome discontinuity (F, inset, arrowhead), acroplaxome distortion (F,G) and nuclear shape irregularity to symmetric manchette appearance with a conical shape (F). Black arrows indicate the perinuclear ring of the machette. (H,I) Step 12/13 spermatids. A membrane-bound microtubular bundle is ectopically located within the nuclear envelope on the presented cross-section (H, inset). The perinuclear ring (I, left arrow) at the left is shifted away from its normal location subjacent to the marginal ring (compare with the perinuclear ring on the right, arrow). (J-L) Step 15/16 spermatids. The mutant elongated spermatids frequently contain deformed nucleus and detached acrosome, with some unidentified materials in the expanded perinuclear space. Acrosome gaps (arrowheads, K) continue to exist. Nu, nucleus; Acr, acrosome; M, manchette. Scale bars: 1 µm.