A Simulation That Students Can Perform

<p>After several minutes, Dpp forms one peak in the centre of the dorsal region, as in the wild type. The various elements of the quantitative model can be entered under “protein conc. changes”, “initial localizations”, “values of constants”, and “initial concentrations”. The numerical simulation itself shows the dynamic behaviour of the designed quantitative model.</p

Two in vivo images showing the first apterous-expressing cells in the wing discs of two flies expressing UAS CD8-GFP under the control of apGAL4.

<p>The wing disc outlines are indicated by the lighter areas. <b>A:</b> In this wing disc, only a single cell shows apterous expression, indicating that although apterous is a marker for the dorsal compartment, the D/V boundary is not established simultaneously with the first apterous expression. <b>B:</b> two cells show apterous-expression. The rather typical position of the first apterous-expressing cells near the tracheal fork is not in accordance with a direct control of apterous via wingless and vein. The scale bar is 50 µm.</p

Images of a wing disc, where the apical cell outlines of the disc proper are marked by GFP fused to E-Cadherin.

<p><b>A:</b> wing disc in vivo at the beginning of the third instar. In this image, several sources of mechanical force can be discerned. A tiny thread is attached to the wing disc on the posterior side (*). Also, the large muscle fiber between the wing, leg and haltere discs is clearly exerting a substantial force on the disc at (**). The cell outlines are correspondingly distorted. <b>B:</b> the same wing disc after dissection. Due to the dissection, the external force from the muscle fiber and the thread has been removed and the shape of the disc as well as that of the cell outlines has relaxed, showing a marked difference to A. The scale bar is 50 µm.</p

Image of the wing and haltere discs in flies expressing UAS CD8-GFP under the control of enGAL4.

<p>This shows the respective engrailed expression patterns. The lighter areas indicate the imaginal disc outlines. In the wing disc (lower left, located above the tracheal branch), the engrailed expression pattern, showing the posterior compartment, is oriented as expected in respect to the larva. In the haltere disc (upper right, located below the tracheal branch) the engrailed expressing cells are oriented quite differently in this stage, although they show the same orientation as the wing disc in later larval stages. This change in orientation over time may be induced by the muscle fiber between the wing, leg and haltere discs.</p

Illustration of the method of locating the wing and haltere discs.

<p>A: Schematic of the process for imaging the larvae and locating the wing and haltere discs. B: A section of the left dorsal trunk, main tracheal branch of a larva showing the positions of the wing(wd) and haltere(hd) discs. The discs are indicated by the lighter areas, the cell outlines are fluorescently marked by GFP fused to E-Cadherin. The thick tracheal branch which connects the right and left main tracheal branches can be seen at the top (+). The wing disc is connected to the first left side branch (*), counting from (+). The haltere disc is located on the second side branch (**).</p

The apterous expression pattern in the left haltere disc over time in flies expressing UAS CD8-GFP under the control of apGAL4.

<p>The haltere disc is indicated by the lighter area. <b>A:</b> first instar haltere disc, without ap expression. <b>B:</b> same haltere disc the next day (about 16(1) h after the first image (AFI)). The larva has entered the second instar and now shows expression of apterous. <b>C:</b> 24(1) h AFI. <b>D:</b> 40(1) h AFI. <b>E:</b> 48(1) h AFI. <b>F:</b> 64(1) h AFI. The larva is in the third instar. <b>G:</b> 72(1) h AFI. In this image it can be seen that the D/V boundary is not yet smooth. <b>H:</b> 88(1) h AFI. The D/V boundary is now smooth and well-defined. <b>I:</b> 96(1) h AFI. <b>J:</b> 112(1) h AFI. <b>K:</b> 120(1) h AFI. The scale bar is 50 µm in all images.</p

The apterous expression pattern in the left wing disc over time in flies expressing UAS CD8-GFP under the control of apGAL4.

<p>The wing disc is indicated by the lighter area. <b>A:</b> second instar wing disc, with first ap expression. <b>B:</b> same wing disc the next day (about 16(1) h after the first image (AFI)). <b>C:</b> 24(1) h AFI. <b>D:</b> 40(1) h AFI. The larva is in the third instar. In this and the following image it can be seen that the D/V boundary is not yet smooth but rather appears to be determined by non-oriented cell divisions<b>. E:</b> 48(1) h AFI. <b>F:</b> 64(1) h AFI. The D/V boundary is now smooth and well-defined. <b>G:</b> 72(1) h AFI. <b>H:</b> 88(1) h AFI. <b>I:</b> 96(1) h AFI. <b>J:</b> 112(1) h AFI. The scale bar is 50 µm in all images.</p

Growth curves of wing disc area during the larval stages.

<p>A: Semi-logarithmic plot of the average apical disc area as a function of time. The times were normalized, such that the first point in the third instar coincided with 80 hrs. The first instar with moderate growth ends after about 24 hrs. In the second (24–72 hrs.) and early third instars, growth is nearly exponential. In the late third instar the slope of the line decreases, indicating a decrease in the average growth rate. The error bars indicate the standard error of the respective time point. Note that in these experiments the larvae are kept at 22(1) °C, which explains the longer time periods of the different growth phases. The vertical lines delineate different instar stages of the larvae. B: Semi-logarithmic plot of the apical disc area for different larvae over time. The average of these growth curves yields the graph shown in part A. Each larva develops individually, yet there is generally moderate growth in the first instar, exponential growth in the second and early third and a decrease in the growth rate in the late third instar. The differences in the growth rates of individual larvae indicate that external factors play a role in wing disc development.</p

In-vivo imaging results.

<p>A: Dependence of the apical cell area on developmental time. B: Proliferation rate as a function of developmental time. The vertical lines indicate the time of the molts between different larval instars. Note the similar time evolution of the area and proliferation rate roughly compatible with a correlation between the two. The correlation is shown in C. Colors correspond to different instar stages (red first instar, blue second instar and black third instar), showing a significant correlation during the growth phase (i.e. in the late second and third instar).</p

The mechanical strain of the tissue during stretching ( when stretching begins).

<p>Shown are the strain in the direction of the applied force () and in the perpendicular direction ().</p