Figure 4.

Genetic cell tracing reveals the continuous proliferation and mitotic division of germ cells. Representative micrographs were obtained at 4 mpi. (a–c) Co-staining EYFP⁺ cells with antibodies to Sycp3 documented a cluster of two or more germ cells that had just divided. None of the daughter cells initiated Sycp3 expression. (d–f) Co-staining EYFP⁺ cells with antibody to Stra8 revealed three modes of germ cell division. Arrowheads in (e) indicated three clustered EYFP⁺ germ cells. Red arrowhead, daughter cell initiating Stra8 expression; yellow arrowhead, daughter cell negative for Stra8; white arrowhead, germ cell negative for Stra8. (g–i) Different modes of germ cell division revealed by immunostaining EYFP⁺ germ cells with antibodies to Oct4 and Dazl. EYFP⁺ germ cells at metaphase (j) and anaphase (k). (l) After tracing for 4 months, EYFP⁺ germ cell (arrowhead) undergoes bona fide mitotic proliferation as indicated by the active BrdU incorporation and the absence of Stra8 expression. (m) After tracing for 4 months, EYFP⁺ germ cell (arrowhead) undergoes pre-meiotic DNA replication as evidenced by the active BrdU incorporation and the Stra8 expression. At each time point, ovaries from two to three animals were used for investigation. Scale bar, 10 μm.