Subcellular processes in morphogen gradient formation studied with 3D tracking fluorescence microscopy

Abstract

A human consists of billions of cells. All these cells need to know in which organ they are located and what their position inside the organ is. One way to obtain this information is via morphogens, small particles providing positional information. We quantitatively studied the transport of the morphogen Decapentaplegic (Dpp) in the __wing imaginal disc__ (the precursor of the wing) of fruit fly larvae. Certain cells in this disc produce Dpp, while others receive it and determine their position according to the Dpp concentration. To study Dpp transport we first developed a microscope able to follow single molecules in three dimensions in living tissue with high spatial and temporal accuracy. With this microscope we then studied the subcellular processes governing intracellular Dpp transport. We determined how long Dpp resides in different types of endosomes (a cellular compartment involved in transport). We also found that the movement of endosomes is too small to facilitate Dpp transport. Furthermore we found differences in the in- and outflow of Dpp in endosomes. This work is one of the first to quantitatively study intracellular morphogen transport. It provides new insights into growth and development of organisms.