Examples of spatial assignments of two wing disc lines, illustrating the logic used to make these assignments. The examples shown in these cartoons are a few of the genes used to assign spatial identity to cell lines; a more complete list can be found in Table 3. The top panel shows a fate map of a Drosophila wing disc (based on a figure from (Held 2002). The middle panel illustrates the sites of expression of three genes expressed in line D21: Optix expression is confined to a small area of the prospective wing blade, straddling the dorsal/ventral (D/V) boundary near the proximal portion of the anterior wing blade (outlined in yellow). fng is a marker for the dorsal compartment in the wing blade and part of the hinge and notal regions (dark blue). Ser is expressed widely in the dorsal compartment, but in the wing blade region, it is confined to the region just on the dorsal side of the D/V boundary (green). Line D21 therefore has expression properties suggesting an origin in the small region colored red. The bottom panel illustrates the sites of expression of three genes expressed in line D32. Gr23a is expressed strongly in this line; taste receptors in the adult (presumably including Gr23a) are confined to the anterior margin of the wing blade, derived from the region of the D/V boundary within the anterior compartment (thick purple line). Dl is expressed in a line of cells on each side of the D/V boundary (dashed blue lines). fng, as described above, is a marker for the dorsal compartment in the wing blade region (dark blue). The region whose expression resembles D32 therefore is somewhere along the red line, just dorsal to the D/V boundary within the anterior compartment.
