FIG. 4.

Meiotic spindles do not form properly in mtsh. Phase-contrast (A, C, E) and fluorescence (B, D, F) micrographs of male meiotic cells from wild-type (A, B, E, F) and mtsh^Z2-2620/mtsh^Z2-2620 (C, D) flies carrying a β tubulin-EGFP transgene (gift from H. Oda and Y. Akiyama-Oda). Wild-type cells in meiosis I (A, B) have strongly fluorescent regions of overlapping microtubules from opposite asters (B, arrows), along with a region of the spindle (arrowhead) thought to be anastral and nucleated from the chromosomal region (Rebollo et al., 2004). Cells from mtsh mutant males (C, D) do not have the overlapping astral spindle region and appear to contain only the anastral central spindle (D, arrowhead) plus some nonoverlapping astral microtubules. In wild-type cells at telophase I (E, F), strong fluorescence from the astral central spindle is detected in the region of the cleavage furrow and contractile ring (arrow). No such furrowing cells are ever observed in mtsh flies. The identical phenotype is seen in mtsh^Z2-2620/mtsh^Z2-3484 and mtsh^Z2-2620/mtsh^55207-12 transheterozygotes. Scale bar 10 μm.