#germline stem cells

Stem Cell -lll

Which factor prevents differentiation in Drosophila GSCs?

In Drosophila ovary, cap cells located at terminal filament tip secrete Decapentaplegic, activating BMP pathway in adjacent germline stem cells to maintain identity. Phosphorylated Mad-Medea complex directly silences transcription of bag-of-marbles, encoding differentiation-promoting factor required for cyst formation and meiosis entry. High local BMP concentration sustains self-renewal, prevents premature differentiation, and represses bam via heterochromatin modulation. Daughter cells displaced from niche experience BMP attenuation, de-repress Bam, and initiate four synchronous transit-amplifying divisions leading to oocyte and nurse cells, constituting bistable switch.

Ref: Song et al., Development 2004; Gilbert, Chap 6: BMP signaling represses Bam preventing GSC differentiation Drosophila.

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Stem Cell -lll

What is the key regulator of the Drosophila ovarian germline stem cell (GSC) niche?

Drosophila ovarian germline stem cells reside at anterior tip contacting cap cells that secrete Decapentaplegic and Glass bottom boat, Drosophila BMP homologs. BMP ligands bind Thickveins and Saxophone receptors, phosphorylating Mad which complexes with Medea to repress bag-of-marbles, the key differentiation factor. This short-range TGF-beta signal maintains GSC self-renewal only within one cell diameter of niche. As cystoblasts move posteriorly, BMP decays, Bam accumulates, and differentiation proceeds through four mitotic divisions with incomplete cytokinesis, demonstrating niche-dependent spatial control of stemness.

Ref: Xie & Spradling, Science 1998; Gilbert, Chapter 6: Drosophila germline stem cell niche BMP Dpp signaling mechanism.

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Morphogen Induction-l

Which factor prevents differentiation in Drosophila germline stem cells (GSCs)?

Drosophila germarium contains germline stem cells anchored to somatic cap cells forming stem cell niche at anterior tip. Cap cells secrete Decapentaplegic, fly BMP2/4 ortholog, activating TGF-beta receptors thickveins and punt on adjacent germline stem cell. Ligand binding phosphorylates Mad, homolog of Smad1, which partners with Medea to repress transcription of differentiation factor bag-of-marbles called bam. Repression maintains self-renewal and prevents cystoblast formation and meiosis entry. When daughter cell moves away from source, BMP signal declines, bam derepressed triggering differentiation into cystocyte. JAK-STAT maintains somatic niche cells, Notch and FGF not primary differentiation inhibitors here for germline.

Ref: Xie and Spradling, Science 1998, BMP Maintains Drosophila Germline Stem Cells.

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Specification Determination-ll

Which of the following factors prevents differentiation in Drosophila germline stem cells (GSCs)?

Germline stem cells in Drosophila ovary and testis are maintained by niche-derived BMP signals. Cap cells secrete Decapentaplegic and Glass bottom boat ligands that activate Thickveins receptors on adjacent GSCs, leading to phosphorylation of Mad and suppression of bag-of-marbles differentiation factor. Repression of bam keeps stem cells undifferentiated and proliferative. As daughter cystoblast moves away from niche, BMP concentration drops, bam is derepressed and differentiation proceeds through four transit divisions. Loss of BMP causes premature stem loss, while ectopic BMP expands stem pool, illustrating niche signaling sustaining self-renewal.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 5: Niche Signaling and BMP in Germline Stem Cells.

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