They also serve as ligands for cell receptors, insuring proper communication between cells. Slit is a complex extracellular protein containing at least four different motifs shared with other differentiation factors and receptors, including the vertebrate epidermal growth factor, the Drosophila receptor Toll, and the matrix protein laminin.
Slit protein is made by midline glial cells.
It provides a matrix for the migration of ventral nerve cord axons and is therefore likely to serve as an axon guidance protein. Robo has been shown to be a repulsive guidance receptor on growth cones that binds to an unknown midline ligand. At the time, because slit had such a similar axon phenotype to single minded , which controls midline cell fate and survival, and because of the lack of good midline markers, there was some uncertainty as to whether slit like sim might also control midline cell fate and survival. As a result, initial attention was placed on robo and comm , two genes that clearly control midline axon guidance. Nevertheless, there was always the lingering possibility that Slit might directly control axon guidance.