Intercalation/closure of the int2 ring.

<p>(A) Left lateral view of the E16 primordium during int2 intercalation/closure; note that cells flanking 2L do not appear to undergo dorsal constriction. In this embryo, 2R intercalations lags 2L intercalation, but 2L does not cross the dorsal midline to connect with 2R. (B) Diagram of the two modes of int2 intercalation/closure. Before intercalation, 2L shifts clockwise across ventral neurons and behind the ventral midline valve cell, v3V (red dashed outline). The int1 cells spread ventrally prior to division, across the anterior face of the int2 cells. The int2 cells either intercalate to close the ring and then rotate clockwise (mode 1), or 2L stalls and 2R completes the ring by rotating across the dorsal midline (mode 2). (C) Transverse view of int2 intercalation, mode 1, from the 3D reconstruction. (D) Transverse view of int2 intercalation, mode 2. The dorsal extension of 2L stopped when 1L divided, and the ring was closed by 2R. (E) Left side view of int2 intercalation, mode 2. Here, 2L extends dorsally between 321 and 329 minutes, at which point 1L divides and 2L stalls. Int2 closure occurs only after 2R reaches 2L on the left side. Note that the elapsed time from extension to closure is 58 minutes in this embryo, compared to 24 minutes for mode1 in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005950#pgen.1005950.g004" target="_blank">Fig 4C</a>. Panels = A,D,E [JJ2360]. Bars = 5 microns.