Figure 7.

Meiotic Chromosomes Failed to Undergo Normal Condensation and Rarely Carried Hypomethylated Histone H3K9 at Pericentromeres in PMCs of mel1-1 Mutants.

(A) Frequency of PMCs at various meiotic stages in anthers ranging from 0.5 to 1.1 mm in length. Blue and red bars indicate the frequency of wild-type and mutant PMCs at the various stages. Arrows indicate the frequencies of escape from meiotic arrest in the mutant (each was 5% or less).

(B) to (I) Indirect immunofluorescence of PMCs. In each section, the left and middle panels represent the results using anti-dimethylated H3K9 (green) and anti-Os CenH3 (red) antibodies, respectively, and both images are merged in the right panels with the chromatin image counterstained with TO-PRO-3 (Invitrogen) (blue). Bars = 5 μm.

(B) to (E) In wild-type PMCs, H3K9 was dimethylated extensively, but mainly at pericentromeric regions during leptotene (B), zygotene (C), pachytene (D), and anaphase I (E).

(F) to (H) Of the mel1-1 PMCs arrested at early meiosis I, most were dimethylated to a normal (F) or moderate (G) level, but markedly hypomethylated PMCs appeared at low frequency (H).

(I) All PMCs that had escaped from meiotic arrest in mutants were dimethylated on H3K9 at a wild-type level.