Before revision:  We then introduce an alternative for gradient formation via the coupling of the proteins within a single cell with a molecule  whose action is similar to that of morphogens in multi-cell assemblies ; the "morphogen" is produced with a fixed flux at one side of the cell.
After revision:  We then introduce an alternative for gradient formation via the coupling of the proteins within a single cell with a molecule whose action is similar to that of morphogens in multi-cell assemblies , the pronogen is produced with a fixed flux at one side of the cell.