Dynamic Regulation of Mitotic Arrest in Fetal Male Germ Cells

Abstract

During fetal mouse development, germ cells enter the developing gonad at embryonic day (E) 10 -11. In response to signaling from the male or female gonad, the germ cells commit either to spermatogenesis at E12.5 and enter mitotic arrest or to oogenesis and enter meiotic arrest at E13.5. It is unclear whether male commitment of the germ line and mitotic arrest are directly associated or whether they are developmentally separate. In addition, the published data describing the timing of mitotic arrest are inconsistent, and the molecular processes underlying the control of the cell cycle during mitotic arrest also remain unknown. Using flow cytometric techniques, 5-bromo-2-deoxyuridine labeling, and immunofluorescent analysis of cell proliferation, we have determined that germ cells in the embryonic mouse testis arrest in G0 during E12.5 and E14.5. This process is gradual and occurs in an unsynchronized manner. We have also purified germ cells and analyzed molecular changes in male germ cells as they exit the cell cycle. This has allowed us to identify a series of molecular events, including activation of p27 Kip1 , p15 INK4b , and p16 INK4a ; the dephosphorylation and degradation of retinoblastoma protein; and the suppression of CyclinE, which lead to mitotic arrest. For the first time, the data presented here accurately define the mitotic arrest of male germ cells by directly combining the analysis of cell cycle changes with the examination of functionally defined cell cycle regulators. STEM CELLS 2008;26:339 -347 Disclosure of potential conflicts of interest is found at the end of this article.

Targeting theGdnfGene in peritubular myoid cells disrupts undifferentiated spermatogonial cell development

“…S2E). In addition, sections of testes from 2-wk-old WT, Het, and cKO mice were immunostained with antibodies to GATA4, a marker for Sertoli cells, and to KI67 (Table S1), a marker for cell proliferation (27)(28)(29). All tubules in WT and Het mice contained KI67-labeled germ cells, whereas some tubules in cKO mice lacked KI67-labeled germ cells (Fig.…”

Primordial Germ Cells in Mice

“…At the fertilization with a haploid spermatozoon, the oocyte completes the second meiotic division and extrudes the second polar body. In contrast to those in the female, XY PGCs enter into mitotic arrest upon entry into the genital ridges, and stay quiescent in the G 0 /G 1 phase of the cell cycle for the remaining embryonic period (Hilscher et al 1974;Western et al 2008). Around day 5 postpartum (P5), many of them resume active proliferation, while some are recruited as spermatogonial stem cells (SSCs) (Fig.…”

Sex determination in mammalian germ cells: extrinsic versus intrinsic factors

“…Germ cells in the developing testis do not enter meiosis but instead stop proliferating, enter G 0 /G 1 arrest, and commit to the spermatogenic pathway (Hilscher et al 1974, McLaren 1984, Adams & McLaren 2002, Western et al 2008. It is not clear whether the events of mitotic arrest and commitment to spermatogenesis occur cell autonomously in the absence of entry into meiosis, or whether they are triggered by extrinsic signals from the testicular soma.…”

“…When XY germ cells in a testis arrest, there are transcriptional changes in some genes encoding cell cycle regulators (Western et al 2008) as well as an upregulation of transcription of the g isoform of Trp63, a relative of Trp53 (Petre- Lazar et al 2007). In addition, the P27 protein appears as germ cells enter mitotic quiescence (Western et al 2008).…”

“…When XY germ cells in a testis arrest, there are transcriptional changes in some genes encoding cell cycle regulators (Western et al 2008) as well as an upregulation of transcription of the g isoform of Trp63, a relative of Trp53 (Petre- Lazar et al 2007). In addition, the P27 protein appears as germ cells enter mitotic quiescence (Western et al 2008). RB1 is a major cell cycle regulator, and it has recently been demonstrated that the active non-phosphorylated form is present in the fetal testis, whereas only the inactive phosphorylated form is present in the fetal ovary (Western et al 2008, Spiller et al 2010.…”