Figure 4.

TEM Analyses of Testes from the Ttc21a Mutant Male Mice Reveal Structural Defects of the Connecting Piece During Spermiogenesis

(A–D) Representative ultra-structures of testicular spermatids from wild-type (WT) male mice during spermiogenesis. Golgi apparatuses were forming acrosomes (A), and the proximal centriole was transplanted into the nuclear fossa (B) in round spermatids. The connecting piece was formed by the assembly of the capitulum, proximal centriole, and segmented columns, and it was attached to the basal plates at the implantation fossa during nuclear condensation (C). In the late, elongated spermatid, the axoneme was surrounded by mitochondria and the forming mid-piece (D).

(E–L) Ultra-structures of testicular spermatids from the Ttc21a^mut/mut male mice during spermiogenesis. No obvious abnormality was observed in the early deformation stage of the round spermatid (E–J). However, during nuclear condensation and the late deformation stage, abnormal formations of the connecting pieces were observed. The structures indicated by green arrows were columnar, which was consistent with the previously reported structural characteristics of segmented columns.³³ Several similar columnar structures appeared nearby. These columnar structures and annulus were scattered (G and K). The mid-pieces could not be formed without being surrounded by mitochondria and without relocation of the annulus (H and L). The misalignment between nucleus and axoneme was observed as well (H and L).

Abbreviations are as follows: Ac = acrosome; An = annulus; Ax = axoneme; Ca = capitilum; Dc = distal centriole; Fo = fossa; Go = Golgi apparatus; Mt = mitochondrion; Nu = nucleus; Pc = proximal centriole; and Sc = segmented column.