drosophila early development

"When is the Drosophila egg activated?"

"During ovulation

"How does sperm enter the Drosophila egg?"

"Through the micropyle

"Why is polyspermy rare in Drosophila?"

"Only one sperm can physically enter through the micropyle."

"What type of cleavage occurs in Drosophila?"

"Superficial meroblastic cleavage."

"What is centrolecithal organization?"

"Yolk concentrated in the center

"What forms pole cells?"

"Nuclei that migrate to the posterior and become germline precursors."

"What is the syncytial blastoderm?"

"A stage where nuclei share a common cytoplasm before cellularization."

"What drives cellularization?"

"Microtubules first

"What major transition overlaps with cellularization?"

"Mid-blastula transition: slower divisions and onset of zygotic transcription."

"What is the first major movement in gastrulation?"

"Ventral furrow formation as prospective mesoderm invaginates."

"What is germ band extension?"

"Convergence/extension of ectoderm and mesoderm toward the ventral midline

"What is the structure of the Drosophila egg chamber?"

"One oocyte and 15 nurse cells connected by cytoplasmic bridges."

"What do nurse cells do?"

"Produce mRNAs and proteins transported into the oocyte."

"What determines which cell becomes the oocyte?"

"One of two posterior cells retains microtubule organizing center activity."

"What is Gurken?"

"A TGF‑α–like protein that signals to follicle cells to establish axes."

"What receptor does Gurken activate?"

"Torpedo (EGFR) on follicle cells."

"What does the first Gurken signal establish?"

"Posterior follicle cell identity and A‑P axis initiation."

"What rearranges microtubules in the oocyte?"

"Reciprocal signaling between oocyte and posterior follicle cells."

"What proteins help organize microtubules in the oocyte?"

"PAR‑3/PAR‑6/aPKC and PAR‑1/PAR‑4 complexes."

"What does the second Gurken signal establish?"

"Dorsal follicle cell identity and D‑V axis initiation."

"Where is Gurken localized during the second signaling event?"

"Anterodorsal region near the oocyte nucleus."

"What gene is repressed in dorsal follicle cells?"

"Pipe."

"Where is Pipe expressed?"

"Ventral follicle cells."

"What does Pipe expression initiate?"

"A serine protease cascade (Gd → Snake → Easter) after fertilization."

"What does the protease cascade activate?"

"Dorsal protein nuclear localization on the ventral side."

"What does Dorsal protein do?"

"Acts as a transcription factor activating ventral genes like Twist and Snail."

"What is Twist?"

"A conserved bHLH transcription factor required for mesoderm formation."

"What are maternal effect genes?"

"mRNAs deposited by nurse cells that set up early gradients."

"What are the key maternal morphogens?"

"Bicoid

"How is bicoid mRNA localized?"

"Transported by dynein to the anterior and tethered there."

"How is oskar mRNA localized?"

"Transported by kinesin to the posterior and tethered to actin."

"What does Oskar protein do?"

"Anchors nanos mRNA at the posterior and allows its translation."

"How is nanos mRNA localized?"

"Diffuses but becomes trapped at the posterior by Oskar."

"What does Bicoid protein do?"

"Acts as a transcription factor activating zygotic Hunchback in the anterior."

"What does Nanos protein do?"

"Translationally represses maternal Hunchback in the posterior."

"What establishes the Caudal gradient?"

"Bicoid represses Caudal translation in the anterior."

"What establishes the Hunchback gradient?"

"Bicoid activates zygotic Hunchback in anterior; Nanos represses maternal Hunchback in posterior."

"What are gap genes?"

"Zygotic genes expressed in broad domains controlled by maternal gradients."

"What regulates Krüppel expression?"

"Activated by Bicoid; repressed by high Hunchback; activated by low Hunchback; repressed by Knirps."

"What are pair‑rule genes?"

"Genes expressed in 7 stripes

"What is an example of a pair‑rule gene?"

"even‑skipped (eve)."

"What controls eve stripe expression?"

"Combinatorial inputs from maternal and gap proteins."

"What are Hox genes?"

"Highly conserved transcription factors specifying A‑P identity."

"What is colinearity?"

"Order of Hox genes on chromosome matches their expression pattern along A‑P axis."

"What demonstrates Hox conservation?"

"Chicken Hoxb‑1 can rescue a Drosophila labial mutant."

"What is the terminal system?"

"Torso RTK signaling at embryo ends."

"What activates Torso?"

"Torso‑like ligand at the poles."

"What does Torso signaling specify?"

"Terminal structures at anterior and posterior ends."

"What is the role of PAR proteins in Drosophila oogenesis?"

"Help organize microtubule polarity for mRNA localization."

"What is the role of the micropyle?"

"Allows sperm entry and prevents polyspermy."

"What initiates D‑V patterning after fertilization?"

"Protease cascade leading to nuclear Dorsal gradient."

"What genes does Dorsal activate?"

"Twist and Snail in ventral mesoderm."

"What genes does Dorsal repress?