Fig. 1. Cell division in the Malpighian tubules. Tubules dissected from wild-type (A,B) and topco mutant (C,D) embryos stained for the incorporation of BrdU to mark S phase. The third postblastodermal division (cycle 16) occurs in a domain on the posterior side of the tubules (arrow in A) and takes place normally in mutant tubules (arrow in C). Only cells in the distal part of the tubules enter cycle 17 (arrow in B). This and subsequent cycles fail in tubules from topco mutants (arrow in D). (E,F) Mutant embryos stained for Cut. The tubules of topco mutant embryos are very small (arrow in E) but are partially rescued in embryos that also carry a deficiency uncovering reaper and hid (tubule cells arrow in F).
