Over the last few years, research has shown that mRNA molecules in the unfertilized egg of Drosophila determine the embryonic axes and future body plan of the fruit fly. The mRNA molecule that specifies the anterior-posterior (head-tail) axis of the embryo is transcribed from an egg-polarity gene which codes for a protein called Bicoid. This gene is active (that is, mRNA is made) in the nurse cells that surround the developing Drosophila egg. The bicoid mRNA, once transcribed, is deposited into the Drosophila egg asymmetrically; the bicoid mRNA is anchored to one end of the egg and not the other. Fertilization of the egg triggers the translation of the maternal bicoid mRNA into protein. The Bicoid protein then diffuses through the egg forming a gradient. The Bicoid protein gradient establishes the polarity of the embryo along the anterior-posterior axis. The head and thorax will develop in the zones of high Bicoid concentration; the abdomen will develop in the region of low Bicoid concentration.