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Axis determination

Maternal effect genes including Bicoid, Nanos,Oskar, Caudal and Hunchback have important roles on axes determination in Drosophila. After being transported from Nurse cells into the oocyte through microtubule, Bicoid mRNAs are shown to localize to the anterior of the embryo while Nanos mRNAs are shown to be tethered to the posterior of the embryo by Oskar protein. After the oocyte is fertilized, Nanos and Bicoid mRNAs are translated, producing two opposing protein gradient, one from the anterior and one from the posterior of the embryo. The two protein gradients would affect the translation of Huntchback and Caudal mRNA which are initially ubiquitously distributed throughout the blastoderm after they are transported from the Nurse cell. Eventually, four maternal protein gradients would be produced (Hunchback and Bicoid protein gradients are established from the anterior part of the embryo while Caudal and Huntchback gradients are established from the posterior part of the embryo). The four protein gradients expressed by maternal mRN initiates the process of axes determination which leads to segmentation and eventually the establishment of cell identities in Drosophila.