FIG. 2.

In mtsh spermatogenesis, mitochondria aggregate and fuse prematurely, and meiotic cytokinesis fails. Phase-contrast (A–N and P–Q) and fluorescence (O) micrographs of live squashed preparations of testes from wild-type (A–H), mtsh^Z2-2620/mtsh^Z2-2620 (I–L and N–Q), and mtsh^Z2-2620/mtsh^Z2-2620; fzo²/fzo^Z3-4436 (M) males. Wild-type primary spermatocyte (A) includes a large phase-light nucleus with phase-dark nucleolus; small, phase-dark mitochondria are diffuse in the cytoplasm. In spermatocytes approaching meiosis (B), the nucleolus becomes less distinct, and mitochondria remain diffuse. In wild-type meiosis I (C) phase-dark mitochondria are aligned on the spindle. (D) After meiosis, mitochondria aggregate (arrow) and fuse beside each daughter nucleus. In early round spermatids (E, F), mitochondrial derivatives form a spherical phase-dark Nebenkern (arrow) beside each phase-light nucleus (arrowhead); the size of the Nebenkern is not affected in preparations not fully squashed (F). Mitochondria unfurl and elongate (G, arrow) and later stretch the full length of each cell within a spermatid bundle (H, partial view). Spermatocytes from mtsh males appear normal (I) but show aberrant and premature mitochondrial aggregation (J, arrow) in cells approaching the first meiotic division. (K) Cyst of mtsh spermatocytes in which mitochondrial aggregation has progressed further in some cells than in others. Aggregating mitochondria (white arrow) appear to form a shell (black arrow) eclipsing each premeiotic nucleus (white arrowhead). (L) Live testis preparation not fully squashed; mtsh nuclei appear surrounded by mitochondrial shells. Compare to panel (F). (N, O) Fully squashed and Hoescht-stained mtsh postmeiotic cells under phase-contrast optics (N) and fluorescence (O); four smaller nuclei (e.g., arrowhead) of roughly the size found in normal haploid spermatids (see panel E) have escaped one mitochondrial shell. (P) Later-stage mtsh spermatids squashed after mitochondrial fission and unfurling; each mitochondrial aggregate separates into four nucleus-associated lobes (arrow) under cover slip pressure. (Q) Elongating spermatid bundles in mtsh, with wide parallel arrays of elongating mitochondria (arrow). Transheterozygotes showed identical phenotypes. Scale bars 10 μm. Panels (A–G) and (I–P) at same magnification; (H) and (Q) at same magnification.