Drosophila formation PP

How does the body at an embryonic stage even know where to place all the organs in such perfect order? The drosophila's dorsoventral axis formation is a good model system to give us a general idea. At an early stage, the drosophila undergoes syncytial specification – in short, it is one cell full of nuclei in the same cytoplasm and they signal each other. Along the cytoplasm, there are genes creating proteins in different concentrations to establish different axes, including the dorsoventral axis. Gurken is a protein that starts off a signaling cascade that leads to the determination of the ventral identity. Dorsal protein controls the ventral identity of the embryo. Toll protein assists in transporting dorsal into the nucleus of the ventral side, where it acts a transcription factor to establish the identity. Another protein called cactus helps by preventing dorsal from entering and hence dorsalizing that end. To prove this theory, Roth et al had performed immunolocalization and Western blots to find location of the proteins in the wildtype, dorsalized and ventralized embryo. In short, it is the difference in concentrations of dorsal in the cytoplasm and the nucleus that creates the morphogenic gradient, which leads to the embryo to have a dorsoventral axis. In fact, the morphogenic gradient is a concept that can be seen in other settings too. For example, when our hands our forming, the the placement of our fingers from our thumb down to our little finger depends upon morphogenic gradient of a certain protein.