Fig. 6. MLH1, RPA and BLM foci at meiotic prophase. (A) MLH foci (orange) appear in association with the SCs (green) when there are only a very few RPA foci (blue) left and there is no obvious colocation at this time. (B) BLM foci (red) are still fairly abundant when the MLH1 foci (green) are present in their nearly full complement of 20-30 foci. There does not appear to be colocation of BLM with MLH1. (C,E) Evidence that MLH1 antigen, which is marked by 5 nm gold grains, locates to the EM-defined RNs. The RNs are the dark-stained (PTA) bodies in association with the SCs. In the nuclei that are positive for MLH1, each SC has one or two immunogold labeled RNs. (D) The bar graph illustrates the decline in immunofluorescent BLM foci, whereas the numbers of MLH1 foci remain relatively constant at late pachytene. (F,G) A precocious diplotene bivalent that was generated by a 2 hour okadaic acid treatment of a pachytene bivalent demonstrates the presence of an MLH1-labeled RN at the site of a presumptive chiasma/crossover.

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