Fig. 4. scab is expressed in pupal intervein cells. scb expression during vein development was monitored by in situ hybridization using a scb antisense RNA probe. scb expression is absent in larval wing imaginal discs (not shown). (A) At 20 hours apf, scb expression is observed in intervein and vein cells. (B) At 25 hours apf scb expression in the interveins is maintained while vein expression becomes weaker. Metalloproteases that cleave Sog are expressed in intervein cells as revealed by RNA probes for tld (C) and tok (not shown). (D) dpp is expressed in the center of provein domains during pupal development, as shown for the L3 vein, while sog is expressed in the intervein cells (E), with peak expression often observed at the border of the provein territory. (F) High magnification view of scb expression in the L3 provein domain at 25 hours apf, showing that staining is excluded from the outermost provein area.