Figure 3. Cells rearrange and change both identity and polarity during larval development.
(A–D) Four individuals are shown; on the left as embryos (A–D) while the right column shows the same four individuals as pre-L3 larvae (A’–D’). The drawings indicate the disposition of the cells of each marked clone (apical profiles filled in green) in the individual embryo and larva respectively. Clones were induced with sry.FLP in the blastoderm stage, studied in the later embryo in the pre-L1 stage and then revisited in the pre-L3. The cells of the clones are marked with cherry::moesin (red cell membranes and pre-denticles), stinger::GFP and Cd8::GFP. All the cells, clone and non-clone are marked with utrp::GFP (pre-denticles are labelled in green) and DE-cad::tomato (cell outlines labelled in red). Numbers I–VII indicate the lines of cells while numbers 1–7 mark the rows of pre-denticles in the embryo (green digits) and the larva (red digits). The cells labelled with single black dots are the T1 tendon cells. Scale bars are 10 µm. (A–A’) Clone of four cells. In the embryo, cells of the clone mark pre-denticles of row 1. In the larva (A’), cells mark pre-denticles of both row 0 (1 cell) and row 1 (3 cells). (B–B’) Clone of two cells. In the pre-L1 embryo, cells in the clone mark pre-denticles of row 2. In the pre-L3 larva (B’), the same cells are the tendon cells. No pre-denticles are marked in the larva. (C–C’) Clone of two cells. In the embryo, cells in the clone mark pre-denticles of row 3 while in the larva the same two cells mark pre-denticles of row 2. (D–D’) Four marked cells in the denticle belt. In the embryo, two cells mark pre-denticles of row 4 and in the larva these same cells mark pre-denticles of row 3. In the embryo two cells make pre-denticles of row 5 and are, presumably, tendon cells. In the larva these same cells make frank T2 tendon cells. Note the tendon cells are small with smaller nuclei, presumably of lower polytenic values than the epidermal cells. Note in Figure D’ that there is a muscle from the adjacent more anterior segment labelled with utrp::GFP and that this muscle attaches to a T1 cell, the most anterior cell of the segment—exactly as in the adult (see Krzemień et al., 2012). See further cases of clones in Figure 4.