Fiber DNA studies of premeiotic mouse spermatogenesis.

The technique of fiber DNA measurement was used to study the possibility that the lengthening of the DNA "S" phase previously reported for mouse premeiotic spermatogonia was due to a reduced number of initiation sites. The mean replicon size of neonatal mouse preleptotene cells was similar to sizes reported for adult mouse somatic cells. A slow rate of DNA chain growth was observed in all cells from day 1 through days 10-12 of age. It was felt that the meiotic entry in male mouse germ cells may involve a slower replication fork rate and other factors which increased the time between activation and replication of replicon families.