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. 1998 Sep 1;12(17):2698–2710. doi: 10.1101/gad.12.17.2698

Figure 5.

Figure 5

clb5/clb5 clb6/clb6 mutants attempt to progress through meiotic development despite being unable to replicate DNA. (A) Northern blots made with RNA samples from sporulating wild-type diploids (left) or clb5/clb5 clb6/clb6 mutants (right) were sequentially hybridized with probes recognizing RNA transcripts from the early (IME1 and IME2) and middle (SPS1 and SPS2) sporulation genes and the B-type cyclins, CLB1 and CLB3. The constitutively expressed gene C4/2 was used as a loading control (Su and Mitchell 1993). (B) Chromatin segregation in wild-type diploids (top) or clb5/clb5 clb6/clb6 mutants (bottom) following induction of sporulation. The proportion of cells having either one (█), two (▴), or more than two (•) masses of divided chromatin was determined by fluorescence microscopic examination of DAPI-stained cells following induction of sporulation in synchronized populations. (C) Chromatin masses in a representative group of cells from the 8-hr time point of B. Chromatin was visualized by propidium iodide fluorescence and is overlaid on a DIC image of the same cells. The wild-type cells (top) have undergone MI and MII, whereas most of the clb5/clb5 clb6/clb6 mutants (bottom) have apparently undergone a single meiotic division. (D) Meiotic spindles visualized by GFP–tubulin fluorescence in wild-type (top) and clb5/clb5 clb6/clb6 (bottom) 6 hr following the induc-tion of sporulation. The fluorescence image is overlaid on a DIC image of the same cells. (E) Lethal meiosis of clb5/clb5 clb6/clb6 mutants is partially rescued by inhibiting spindle formation. Viability in synchronized populations of wild-type (□,█), clb5/clb5 (○,•) or clb5/clb5 clb6/clb6 (▵,▴) mutant cells treated (solid symbols) with nocodazole (20 μ/ml)/benomyl (30 μg/ml) or left untreated (open symbols) following induction of sporulation.The percent of viable cells was determined by their ability to return to mitotic growth when removed from sporulation conditions and plated onto rich growth medium lacking any inhibitors. Values represent the average number of colonies derived from two independent samples.