Figure 7. SMC-4 and MIX-1 co-localize with centromere proteins on meiotic chromosomes, and their depletion impairs chromosome segregation in meiosis II but not meiosis I. (A-D) Meiosis I bivalents stained with a DNA dye (blue, A), SMC-4 antibody (green, B), and an antibody to centromere protein HCP-3 (red, C). SMC-4 is concentrated at the periphery of the chromosomes and colocalizes with HCP-3. (D) SMC-4 and HCP-3 overlap (yellow). (E-H) Images of anaphase I (ana I) and anaphase II (ana II) from time-lapse movies of meiosis in a strain carrying histone H2-GFP. Normal segregation of homologs at anaphase of meiosis I is observed in wild-type (E) and
smc-4(RNAi) embryos (F). Sister chromatids separate normally at anaphase of meiosis II in wild-type embryos (G; PB1 is first polar body from meiosis I), but anaphase II chromatin bridges are observed in
smc-4(RNAi) embryos (H; PB1 is out of focus). (I-J) DNA-stained wild-type (I) and
smc-4(RNAi) (J) embryos after formation of the first and second polar bodies (PB1 and PB2) and migration and fusion of the oocyte (O) and sperm (S) pronuclei. In
smc-4(RNAi) embryos, the oocyte pronucleus remains connected to the second polar body by a long chromatin bridge; condensation of prophase chromosomes in the pronuclei is abnormal (J).