Fig. 7. Proliferation profile of the lymph gland. (A) Second instar primary lobe stained for BrdU incorporation. A single confocal section from the middle of the lymph gland shows BrdU (red) incorporation in randomly positioned cells. (B,B') Third instar primary lobe stained for BrdU incorporation. A single confocal section from the middle of the lymph gland shows that BrdU⁺ cells (red) are restricted to the cortical zone marked by Pxn expression (B', green). (C) Cells incorporating BrdU (red) are excluded from the medullary zone marked by dome-gal4/UAS-GFP (green). (D) Quantitation of data represented in C. Twelve third instar lymph gland lobes were counted. The y-axis represents the percentage of total BrdU-positive cells. (E) In secondary lobes of the third instar lymph gland, BrdU⁺ cells (red) are randomly distributed. To-pro-3 (blue) marks nuclei. Scale bars: 10 µm. (F) Three phases of proliferation in lymph gland development. Phase 1: growth phase. Lymph gland cells expand in number from the embryonic stage through the second instar (left panel). Cells in the secondary lobes of the third instar also belong to this phase. Phase 2: quiescence phase. This comprises the prohemocyte population of the third instar medullary zone. Cells of the PSC also rarely divide. Phase 3: expansion phase. Maturing and mature hemocytes divide to increase their numbers.