- Torpedo, is known to serve as a receptor for Gurken. Deficiencies of the torpedo gene in Drosophila cause ventralization of the embryo. In an experiment, the germ cell precursors from a wild type embryo were transplanted into embryos whose mother carried the torpedo mutation. Also, the reverse experiment, i.e., transplantation of germ cell precursors from torpedo mutants into wild type embryos was done. The torpedo deficient germ cells developed in a wild type female showed normal dorso-ventral axis, while the wild type germ cells developed in a torpedo deficient female showed ventralized egg. Some of the following
statements are drawn from the above experiments and some from known facts to understand the functioning of Torpedo.
A. Zygotic contribution of Torpedo is essential for the development of dorso- ventral axis.
B. Maternal contribution of Torpedo is essential for the development of dorso- ventral axis.
C. Since Torpedo is a receptor for Gurken and follicle cells surround the part of the oocyte where Gurken is expressed, it is likely that Torpedo is expressed in follicle cells.
D. Gurken signalling initially dorsalizes the follicle cells, which in turn send signal to organize the dorso- ventral polarity in oocyte.
E. Gurken signalling initially dorsalizes the nurse cells which help in generation of dorso-ventral polarity in oocyte.
Which one of the following combination of statements is most appropriate?
(1) B, C and D (2) A, C and D
(3) B, C and E (4) A, D and E
The establishment of the dorsal-ventral (D-V) axis in Drosophila melanogaster is a finely tuned developmental process governed by signaling between the oocyte and surrounding follicle cells. Central to this process is the interaction between the Gurken protein, secreted by the oocyte, and the Torpedo receptor (Drosophila EGFR) located on follicle cells. This interaction directs the dorsal fate of follicle cells, which in turn orchestrates subsequent embryonic patterning steps.
Maternal Contribution of Torpedo Is Essential
Experiments with germ line chimeras demonstrate the importance of maternal, rather than zygotic, Torpedo function in D-V axis determination. When torpedo mutant germ cells develop in a wild type ovary, normal dorsal-ventral patterning is rescued by the maternal somatic environment. Conversely, wild type germ cells in torpedo mutant ovaries fail to establish dorsal follicle cell fate, leading to ventralized embryos. This confirms that maternal Torpedo receptor expression in follicle cells, not zygotic Torpedo, is essential for D-V axis formation.
Expression of Torpedo in Follicle Cells and Its Role
The Torpedo receptor is expressed specifically in follicle cells surrounding the oocyte, particularly those dorsal to the oocyte nucleus where Gurken protein accumulates. Gurken binds to Torpedo, triggering signaling cascades that induce dorsal identity in these follicle cells. This localized dorsalization is the first step in establishing spatial cues that define the embryonic dorsal side.
Gurken Signaling Dorsalizes Follicle Cells for Embryonic Patterning
Gurken signaling to follicle cells modifies their fate, which then produce factors influencing the oocyte to organize the dorsal-ventral polarity. This follicle cell feedback is crucial for asymmetric patterning of the future embryo. There is no evidence that Gurken directly dorsalizes nurse cells; rather, the follicle cells respond to Gurken to mediate polarization.
Summary of Correct Statements
-
Statement B: Maternal contribution of Torpedo is essential for D-V axis development — true.
-
Statement C: Torpedo is expressed in follicle cells surrounding the oocyte — true.
-
Statement D: Gurken signaling dorsalizes follicle cells which organize D-V polarity — true.
-
Statement A (zygotic Torpedo essential) and Statement E (Gurken dorsalizes nurse cells) are incorrect.
Conclusion
The most accurate combination explaining the function of Gurken and Torpedo in dorsal-ventral polarity is (1) B, C, and D. Maternal Torpedo receptor in follicle cells mediates Gurken signaling to establish dorsal follicle cell fate, thereby indirectly shaping the embryonic dorsal-ventral axis.
-
6 Comments
Kajal
November 12, 2025B,C and D
Bhawna Choudhary
November 13, 2025B C D is correct
Rishu
November 13, 2025B ,c and d is the right answer
Mohd juber Ali
November 15, 2025B C D is right
Santosh Saini
November 16, 2025B , C , D is right
Muskan Yadav
November 21, 2025(1) B, C, and D is the correct statement.