Recombination intermediates in Blm^cko/neo spermatocytes. (A–C) Early and late recombination nodules appear in normal numbers (A and B) and with normal localization as measured by MSH4 (A) and MLH1 (B and C) foci counts. MSH4 and MLH1 foci were counted for Blm^flox/neo (black) and Blm^cko/neo (gray) mice. The mean values are represented by black horizontal lines. (C) Both Blm^flox/neo (left) and Blm^cko/neo (right) mice were stained with antibodies against SYCP3 (red) and MLH1 (green). (D) MLH1 localizes in cells with and without BLM localization. (left and middle) Dual staining of pachytene spermatocytes from Blm^cko/neo mice with antibodies against MLH1 (green), BLM (red), and DAPI (blue) in the absence of any staining against synaptonemal complex proteins. BLM staining is absent in some cells from the CKO mouse (left) and present in other cells from the same mouse (middle, red arrows). MLH1 localization (green) is the same in both cohorts of cells. (right) Chromosome cores stained with both SYCP3 and MLH1 (green arrows) coupled with BLM (right, red arrows) show colocalization in the Blm^flox/neo mouse; however, in the BLM-deleted mutant mouse where BLM is absent from some spermatocytes, MLH1 still localizes at a similar frequency to that of control animals.