An Unpaired Mouse Centromere Passes Consistently Through Male Meiosis and Does Not Significantly Compromise Spermatogenesis

ST1 is an artificial mini-chromosome approximately 4.5 Mb in size containing mouse minor and major satellite DNA, human alphoid DNA and sequences derived from interval 5 of the human Y chromosome. Here we have measured the mitotic and meiotic transmission of ST1 and have used the mini-chromosome to define the ability of mice to monitor the presence of unpaired centromeres during meiosis. ST1 is mitotically stable, remaining intact and autonomous in mice for many generations. Female mice efficiently transmit ST1 to their offspring at a frequency approaching 50%. Male mice also reliably transmit the mini-chromosome, though to only 20% of their offspring. Presence of ST1 in males is not associated with any compromise in the output of the seminiferous epithelium nor with histological or immunocytochemical evidence of increased apoptosis, outcomes predicted for a synapsis checkpoint. These data indicate that the presence of an unpaired centromere is not sufficient to arrest male meiosis, implying that univalents are normally eliminated by a mechanism other than a tension-sensitive spindle checkpoint.