This series compares gene expression between germ line stem cells (GSCs) purified either from bam mutant or Dpp-overexpressing ovaries, with gene expression in Kc cells.

RNA from dissected ovary tips of c587-GAL4; hsbam UAS-dpp females 50hr after a single heat shock to induce GSC differentiation ; expt 2; these tips contain reverted GSCs; See Kai et al. (2005). Developmental Biology, in press.

RNA from dissected ovary tips of c587-GAL4; hsbam UAS-dpp females 0hr after a single heat shock to induce GSC differentiation ; expt 2; these tips are enriched in GSCs; See Kai et al. (2005). Developmental Biology, in press.

RNA from dissected ovary tips of c587-GAL4; hsbam UAS-dpp females 0hr after a single heat shock to induce GSC differentiation ; expt 1; these tips are enriched in GSCs; See Kai et al. (2005). Developmental Biology, in press.

RNA from Kc tissue culture cells was profiled. This is replicate 2. See Kai et al. (2005). Developmental Biology, in press.

RNA from Kc tissue culture cells was profiled. This is replicate 1. See Kai et al. (2005). Developmental Biology, in press.

gene expression is tested for an association with GSCs by comparing expression levels in ovary tips of c587-GAL4; hs-bam UAS-dpp females at 0 hr, 20 hr and 50 hr after heat shock ; results of two independent experiments are given as expt 1 and expt 2.

RNA from dissected ovary tips of c587-GAL4; hsbam UAS-dpp females 20hr after a single heat shock to induce GSC differentiation ; expt 1; these tips lack GSCs; See Kai et al. (2005). Developmental Biology, in press.

Drosophila adult females but not males contain high levels of the steroid hormone ecdysone, however, the roles played by steroid signaling during Drosophila gametogenesis remain poorly understood. Drosophila germ cells in both sexes initially follow a similar pathway. After germline stem cells are established, their daughters form interconnected cysts surrounded by somatic escort (female) or cyst (male) cells and enter meiosis. Subsequently, female cysts acquire a new covering of somatic cells to form follicles. Knocking down expression of the heterodimeric ecdysteroid receptor (EcR/Usp) or the E75 early response gene in escort cells disrupts 16-cell cyst production, meiotic entry and follicle formation. Escort cells lose their squamous morphology and unsheath germ cells. By contrast, disrupting ecdysone signaling in males does not perturb cyst development or ensheathment. Thus, sex-specific steroid signaling is essential for female germ cell development at the time male and female pathways diverge. Our results suggest that steroid signaling plays an important sex-specific role in early germ cell development in Drosophila, a strategy that may be conserved in mammals.

Whether or not mammalian females generate new oocytes during adulthood from germ-line stem cells to sustain the ovarian follicle pool has recently generated controversy. We used a sensitive lineage-labeling system to determine whether stem cells are needed in female adult mice to compensate for follicular losses and to directly identify active germ-line stem cells. Primordial follicles generated during fetal life are highly stable, with a half-life during adulthood of 10 mo, and thus are sufficient to sustain adult oogenesis without a source of renewal. Moreover, in normal mice or following germ-cell depletion with Busulfan, only stable, single oocytes are lineage-labeled, rather than cell clusters indicative of new oocyte formation. Even one germline stem cell division per 2 wk would have been detected by our method, based on the kinetics of fetal follicle formation. Thus, adult female mice neither require nor contain active germ-line stem cells or produce new oocytes in vivo.