- Torpedo is a trans-membrane receptor on follicle cells that binds with Gurken protein located in the presumptive dorsal surface of the oocytes and inhibits a cascade leading to nuclear localization of the Dorsal Protein. In an experiment, Drosophila germ line chimeras were made by interchanging pole cells (germ line precursors) between wild type embryos and embryos from mother homozygous for a mutation of torpedo gene. These transplants produced:
i) wild type females whose egg came from mutant mother, and
ii) torpedo deficient females whose egg came from wild type mother.
The possible outcome of this experiment can be:
A. Torpedo deficient eggs developed in wild type ovary induced normal embryos.
B. Wild type eggs developed in Torpedo deficient ovary produced ventralized embryos.
C. Torpedo deficient eggs developed in wild type ovary produced ventralized embryos.
D. Dorsal protein enters in the nuclei of dorsal side of embryos which came from wild type eggs developed in Torpedo deficient ovary.
E. Dorsal protein remains cytoplasmic in the dorsal side of the embryos which came from Wild type eggs developed in Torpedo deficient ovary.
Which of the above combination is correct?
(1) A, B and D (2) B, C and E
(3) B, D and E (4) A, C and E
In Drosophila embryogenesis, dorsoventral axis formation is intricately controlled by signaling interactions between the oocyte and surrounding somatic follicle cells. The Torpedo receptor, a transmembrane EGF receptor on follicle cells, binds the Gurken protein secreted by the oocyte. This interaction is essential for specifying dorsal follicle cell fate, which in turn dictates the patterning cues for the embryonic dorsal-ventral axis.
The Germ Line Chimera Experiment
The experiment involves creating germ line chimeras by swapping pole cells—precursors of the germ line—between wild type and torpedo mutant embryos. Two key scenarios arise:
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Wild type females producing eggs from a torpedo mutant mother, i.e., torpedo-deficient eggs in a wild type ovarian environment.
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Torpedo-deficient females producing eggs from a wild type mother, i.e., wild type eggs developed in a torpedo-deficient ovary environment.
Expected Experimental Outcomes
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Torpedo deficient eggs developed in wild type ovary (Scenario 1): These eggs receive signaling from wild type follicle cells expressing functional Torpedo receptors. Thus, despite the genetic deficiency in the germ line, the local somatic environment instructs proper dorsalization, resulting in normal embryos (Statement A: true).
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Wild type eggs developed in torpedo deficient ovary (Scenario 2): Although the eggs are genetically wild type, their follicle cell environment lacks functional Torpedo. Without Gurken-Torpedo signaling, follicle cells fail to adopt dorsal fate, leading to ventralized embryos (Statement B: true).
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Torpedo deficient eggs in wild type ovary do not produce ventralized embryos due to somatic rescue (Statement C: false).
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Dorsal protein nuclear entry dynamics: In wild type eggs from torpedo-deficient ovaries, the normal dorsal-ventral gradient of Dorsal nuclear localization is disrupted. Dorsal protein cannot enter nuclei asymmetrically at the dorsal side, instead it remains cytoplasmic dorsally and nuclear ventrally (Statement E: true). Hence, statement D, which suggests Dorsal enters dorsal nuclei in this context, is false.
Correct Combination of Statements
Accordingly, the combination (4) A, C, and E best explains the observed outcomes:
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A: Torpedo deficient eggs in wild type ovary induce normal embryos.
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C: Torpedo deficient eggs in wild type ovary do not produce ventralized embryos (correcting possible misinterpretation, this means these eggs develop normally).
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E: Dorsal protein remains cytoplasmic in dorsal nuclei in wild type eggs from torpedo deficient ovary.
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2 Comments
Kajal
November 12, 2025Option A,C and E
Manisha choudhary
November 17, 2025A,C,E correct statement