Damaged chromatin does not prevent the exit from metaphase I in fused mouse oocytes

The presence of checkpoint mechanisms which are able to recognize damagedchromatin and thereafter to prevent exit from metaphase I has beeninvestigated in giant mouse oocytes produced by fusion of a normalmetaphase I oocyte with an equivalent oocyte with damaged chromatin. Thepresence of damaged chromatin did not prevent the onset of anaphase I inboth sets of chromatin in the fused cells. Interestingly, fused or unfusedcells containing only damaged chromatin failed to enter anaphase andpersisted instead in a metaphase-like state. These results demonstrate thefragility of checkpoint controls in mammalian female germ cells.