FIGURE 4 ∣.

Expression of Pf-Pou3 and Pf-Msxlx during head regeneration. (A–E) Whole mount in situ hybridization of Pf-Pou3. (A) At 0 days post-amputation (dpa), no signal is detected in the tissue at the site of transection. (B) At 2 dpa, signal is first detected along the dorsal mid-line (arrowhead) just posterior to the site of transection. Note that at 2 dpa the wound edges are swollen and the wound is still open to the gut (arrow). (C) At 3 dpa, the wound has closed and signal along the dorsal midline has extended anteriorly into the base of the nascent blastema. (D) At 5 dpa and (E) at 7 dpa (dorsal view), a strong signal at the base of the blastema and forming head continues during the course of regeneration. At this time, a weak signal appears throughout the blastema and forming head. (F–H) In situ hybridization of Pf-Msxlx. (F) At 3 dpa, signal is evident along the dorsal nerve track (arrowhead). (G) At 5 dpa and (H) at 7 dpa (dorsal view), signal has extended along the dorsal mid-line to the base of the blastema where it widens into a triangle (arrows). This pattern of expression continues as the new head develops. p, nascent proboscis; c, nascent collar. Dorsal is up in all frames, unless noted. Scale bars = 0.25 mm.