Fig. 1. Monopolar and conical spindles in dd4 testes. (A-F) Living cells at different stages of meiosis in wild-type (A-C) and dd4^S (D-F) testes viewed by phase-contrast light microscopy. (A) Cyst of primary spermatocytes at the onset of meiosis I with parafusorial membranes becoming visible (arrow). (B) This parafusorial material is seen along the meiotic spindle and concentrates in the equatorial region in late anaphase I (arrow). (C) A cyst at the onion stage showing spermatids, each containing a nucleus (light sphere) adjacent to a Nebenkern (phase dense sphere). (D) Cyst of primary spermatocytes from dd4^S testis with an abnormal number of cells. One of the cells is larger than the others (arrow), whereas the morphology of both germline and somatic cells (cyst precursor cell, arrowhead) seems normal. (E) Example of the asymmetric distribution of the phase-dense material in dd4^S meiocytes. Both conical (arrows) and biconical (arrowhead) figures are visible. (F) A cyst of early dd4^S spermatids with very disorganized Nebenkerns (dark inclusions). The nuclei associated with each Nebenkern are variable in size and number (arrow). Note also what seem to be bundles of sperm tails on the right of this cyst. (G-L) Localization of -tubulin (red) with respect to spindle microtubules (green) in spermatocytes from fixed wild-type (G-I) and dd4^S (J-L) testes. DNA is stained blue. (G) A wild-type 16-cell cyst in prometaphase with duplicated and separated centrosomes. (H) Cells in anaphase before formation of the central spindle. (I) Late anaphase/telophase with fully formed central spindle marked by two bands of microtubules (paired arrowheads) separating the central spindle mid-zone (single arrowhead). The -tubulin-containing MTOCs have separated before meiosis II. (J) A dd4^S 16-cell cyst in which condensing chromatin is surrounded by masses of microtubules (arrows) in early meiosis and -tubulin staining is undetectable. (K) Field of dd4^S cells in meiosis showing one cone that has a central spindle-like structure (arrow) separating two masses of chromatin and three hemi-spindles. The DNA in the hemi-spindles is present both at the centre of the asters and around the periphery (e.g. arrowhead). (L) The left-most arrow points to a rare example of a bipolar spindle. The cones in this panel (remaining arrows) show a pronounced constriction at their apexes compared with the cone in panel K. Measurement of the frequency of the different types of defective meiotic figure in a sample of 162 cells indicated that 38% were hemi-spindles, 7% sharp cones and 33% biconical. 22% of this group of cells had a morphology that suggested either apoptosis or necrosis. Bars, (A-F), 20 µm; (G-L), 50 µm.

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