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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
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- Life Sciences
Torpedo, is known to serve as a receptor for Gurken. Deficiencies of the torpedo gene is 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 dorsoventral 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 occyte.
Which one of the following combination of statements is most appropriate ?
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Eduncle Best Answer
The oocyte nucleus is originally located at the posterior end of the oocyte, away from the nurse cells. It then moves to an anterior dorsal position and signals the overlying follicle cells to become the more columnar dorsal follicle cells. Hence statement D is correct and Statement E incorrect.
The dorsalizing signal from the oocyte nucleus appears to be the product of the gurken gene. The Gurken signal is received by the follicle cells through a receptor encoded by the torpedo gene. Hence Statement C is correct.
Maternal deficiency of torpedo causes the ventralization of the embryo.
Moreover, the torpedo gene is active in the ovarian follicle cells, not in the embryo. Hence statement B is also correct.