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#Drosophila

77 public questions tagged with this topic.

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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Morphogen Induction-l

Which one of the following morphogens is involved in anterior-posterior patterning in Drosophila?

Anterior-posterior axis in Drosophila is initially established by maternally localized mRNAs along oocyte cortex. Bicoid transcript anchored anteriorly by cytoskeletal proteins, Nanos posteriorly, creates opposing gradients determining polarity. Bicoid protein diffuses posteriorly forming concentration gradient that activates gap genes hunchback and orthodenticle in threshold-dependent manner specifying head and thorax, while repressing caudal translation posteriorly refining pattern. Notch signaling mediates later segmentation boundary sharpening and neuroectoderm decisions but does not provide primary AP positional information. Thus morphogen driving AP patterning is Bicoid, functioning as anterior determinant and concentration-dependent transcription activator of zygotic genome.

Ref: St Johnston and Nusslein-Volhard, Development 1992, Bicoid Establishes Drosophila AP Polarity.

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Induction Morphogen -ll

Which of the following morphogens is essential for anterior-posterior patterning in Drosophila embryos?

Bicoid mRNA is localized anteriorly in Drosophila oocyte by swallow, exuperantia and staufen proteins anchoring to cytoskeleton. After fertilization, translation creates anterior-to-posterior protein gradient that functions as morphogen for anterior patterning. High anterior Bicoid activates hunchback, orthodenticle and buttonhead to specify head and thorax, while low posterior permits abdomen via repression of Caudal translation. Nuclear Bicoid concentration directly activates gap gene enhancers in threshold-dependent manner via homeodomain binding. Notch, FGF8 and retinoic acid do not provide primary AP axis information in fly embryo; Bicoid together with Nanos posterior counter-gradient establishes anteroposterior polarity.

Ref: Nusslein-Volhard, Drosophila Development, Chapter 2: Bicoid Gradient and AP Patterning.

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Specification Determination-l

What is a key feature of syncytial specification in Drosophila?

Drosophila embryogenesis begins as syncytium facilitating rapid pattern formation. Nuclei divide thirteen times without cytokinesis, sharing common cytoplasm where Bicoid and Nanos gradients diffuse unimpeded, establishing positional information before membranes form. Gap genes respond to gradient thresholds, initiating segmentation cascade of pair-rule and segment polarity genes through cooperative DNA binding. Only after cellularization at cycle fourteen do cells become individualized, retaining pre-programmed identities through sustained transcription factor networks. Key innovation lies in fate pre-patterning within communal cytoplasmic space, accelerating development and minimizing need for extensive early cell-cell signaling during axis establishment phase.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Syncytial Specification Before Cellularization in Drosophila.

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Specification Determination-l

Which type of specification is most commonly seen in Drosophila syncytial blastoderm?

Drosophila early embryogenesis is dominated by syncytial specification, where rapid nuclear divisions occur without cytokinesis, generating a syncytial blastoderm with nuclei sharing common cytoplasm. Maternal gradients including Bicoid, Hunchback and Caudal diffuse among nuclei, establishing positional codes before membranes enclose cells. Gap, pair-rule and segment polarity genes activate sequentially based on threshold responses to these gradients through cooperative enhancer binding. This mode permits long-range morphogen action unrestricted by membranes, distinct from autonomous or conditional mechanisms requiring localized determinants or cell-cell signaling after cellularization and essential for fast insect development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Syncytial Specification in Drosophila Blastoderm.

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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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Specification Determination-ll

In Drosophila, the gradient of which morphogen determines anterior structures?

Anterior structures in Drosophila are patterned by Bicoid, a homeodomain transcription factor functioning as classic morphogen. Its mRNA is localized to anterior pole of the oocyte through cytoskeletal anchoring, and after fertilization translation produces protein that diffuses posteriorly forming exponential gradient in syncytial embryo. Nuclei exposed to high Bicoid activate anterior gap genes including hunchback, orthodenticle and empty spiracles promoting head and thoracic identity. Lack of Bicoid deletes anterior segments and transforms them into posterior telson via ectopic Caudal, while ectopic anterior transplantation duplicates head structures posteriorly, confirming morphogen role.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Bicoid Morphogen Gradient and Anterior Patterning.

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Sex determination-l

Metafemale condition in Drosophila occurs when X:A ratio is:

Import entry appears erroneous listing germ-layer inducers epidermis, Xbra, Goosecoid, neural tube as options for metafemale condition rather than numeric X:A ratios, indicating data import mismatch. Metafemale in Drosophila classically defined as severely abnormal flies with X:A ratio 1.5 corresponding to 3X:2A genotype showing female-like traits but inviable due to dosage compensation abnormalities and developmental defects, sterility and morphological malformations. Normal female 1.0, male 0.5, intersex 0.67. Intended answer Goosecoid marks Spemann organizer in Xenopus unrelated to sex ratio, but metafemale ratio conceptually 1.5.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Metafemale 3X/2A ratio 1.5; organizer Goosecoid confusion noted.

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Sex determination-l

XX males occur due to presence of:

XX male syndrome occurs frequently due to aberrant recombination during paternal meiosis where SRY-containing segment of short arm Y translocates onto distal Xp or autosome. Offspring inheriting recombined chromosome are karyotypically XX but carry functional SRY capable of initiating Sox9 activation and testis determination despite absence of other Y genes such as AZF needed for spermatogenesis. Individuals develop phenotypic males with testes, male internal ducts and external genitalia though typically azoospermic and sterile. Incidence around 1 in 20,000 males reveals sufficiency of SRY for gonadal male development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: XX males due to SRY translocation.

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Sex determination-l

Sex-lethal protein in Drosophila is a:

Sex-lethal protein contains two conserved RNA recognition motifs binding uridine-rich sequences near regulated splice sites modulating spliceosome assembly. Rather than binding DNA as transcription factor, Sxl interacts with U1 snRNP and U2AF complex to block inclusion of male-specific exon with premature stop codons in its own transcript and transformer. This post-transcriptional RNA-splicing factor activity shifts pattern toward female isoforms. Through precise alternative splicing control, Sxl integrates dosage compensation, germline sexual identity and somatic differentiation, orchestrating entire female program via RNA processing rather than direct transcriptional activation of target genes.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 8: Sxl is RNA-splicing regulator.

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Sex determination-l

In Drosophila, X:A ratio of 1.0 indicates:

X:A ratio 1.0 in Drosophila meaning two X chromosomes and two autosome sets provides strong numerator signal activating Sex-lethal establishment promoter. Double dose of transcription factors sis-a, sis-b, scute and runt cooperatively binds SxlPe enhancer driving robust early Sxl transcription around blastoderm. Resulting Sxl protein autoregulates its maintenance splicing avoiding stop-codon exon and triggers female transformer and doublesex isoforms DsxF. Phenotype therefore female with functional ovaries, female pigmentation, dosage compensation off. Ratio 0.5 yields male, intermediate 0.67 intersex, 1.5 metafemale inviable.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: X:A ratio 1.0 indicates female Drosophila.

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