. prdGAL4 driven expression of GMA during germband retraction. The video covers 90 minutes during germband retraction. Each epidermal stripe of expression continues dorsally into the amnioserosa and as the germband retracts the amnioserosal cells stay in register with their corresponding epidermal stripe. Note that the stripes of GMA expression narrow dorsally as they move around the hairpin bend at the end of the embryo.

Mistakes in epidermal cell matching at the dorsal midline can be resolved after dorsal closure. The video covers 100 minutes and shows enGAL4 driven stripes of GMA expression during dorsal closure. Two pairs of stripes mismatch: second from the left and second from the right. The left-hand mismatch resolves immediately; however, the right-hand mismatch is not resolved until after the adjacent pair of GMA-expressing stripes have met. Subsequent to dorsal closure, filopodia and lamellipodia are still active at the dorsal midline.

RhoA^N19 expression alters behavior of leading edge cells during germband retraction. The video covers 50 minutes during germband retraction and shows an embryo co-expressing RhoA^N19 and GMA under the control of prdGAL4. At the beginning, two RhoA^N19-expressing stripes have made ectopic cell-cell connections at their leading edges (bottom right) and another has initiated ectopic contacts via leading edge filopodia. Note that these stripes do not undergo dorsal narrowing (compare with Video 1). Furthermore, amnioserosa cells no longer appear as tightly associated with individual epidermal stripes; an amnioserosal cell associated with the top right prdGAL4 stripe becomes transiently associated with other stripes in the right hand cluster RhoA^N19 expression alters behavior of leading edge cells during germband retraction. The video covers 50 minutes during germband retraction and shows an embryo co-expressing RhoA^N19 and GMA under the control of prdGAL4. At the beginning, two RhoA^N19-expressing stripes have made ectopic cell-cell connections at their leading edges (bottom right) and another has initiated ectopic contacts via leading edge filopodia. Note that these stripes do not undergo dorsal narrowing (compare with Video 1). Furthermore, amnioserosa cells no longer appear as tightly associated with individual epidermal stripes; an amnioserosal cell associated with the top right prdGAL4 stripe becomes transiently associated with other stripes in the right hand cluster.

RhoA^N19 expression alters behavior of leading edge cells during dorsal closure. The video covers 125 minutes during dorsal closure and shows an embryo co-expressing RhoA^N19 and GMA under the control of enGAL4. RhoA^N19-expressing cells at the leading edge spread and put out extensive filopodia. Contact between filopodia from neighboring RhoA^N19 stripes initiates the formation of ectopic cell bridges.

RhoA^N19 expression causes cell defects at the ventral midline. The video covers 120 minutes and shows ventral view of a stage-11 embryo co-expressing RhoA^N19 and GMA under the control of prdGAL4. RhoA^N19-expressing cells spread slightly along the ventral midline. Many then undergo cytoskeletal compaction, resulting in the generation of bright spots of GFP fluorescence.

RhoA^N19 expression causes defects in epidermal cell-cell adhesion. The video covers 75 minutes and shows a ventral view of a stage-12 embryo co-expressing RhoA^N19 and GMA under the control of enGAL4. A ventral epidermal hole is apparent within each RhoA^N19-expression domain and these expand as the lateral epidermis moves dorsally. In addition, cells at the periphery of these holes fall out of the epidermal cell layer and are ingested by hemocytes. This can be seen at the beginning of the video in the stripe of expression second from right. Hemocytes can be seen as motile shadows and are observed to transmigrate between RhoA^N19-expressing cells. This is particularly clear in the third expression stripe from the left, where four hemocytes penetrate the epidermis creating an increasingly larger ventral hole.