Transmission electron micrographs of sperm heads from the epididymis from Hnrnpab^−/− and Hnrnpab^+/− mice.

<p>(A) Normal sperm from Hnrnpab^−/− mouse showing the nucleus (n) revealed like an evenly stained black mass (due to high electron density) that contains the highly compacted DNA, surrounded by the nuclear envelope. The acrosome (a) located in the anterior half of the head and the proximal centriole (pc) in the neck of the sperm. (B) Abnormal sperm of Hnrnpab^−/− mice with fibers extending out of the main mass of local regions of nucleus (inset in B and B′). (C) Abnormal sperm of Hnrnpab^−/− mice with fibers extending out of the main mass around the nucleus (inset in C and C′). (D) Elongated spermatid at step 13 of spermatogenesis of wild-type mice. Posterior part of DNA, which is less packed than in anterior region, was observed as fibers (inbox in D and D′). Scale bar is 2 µm in A–D and 500 nm in B′–D′.