Fig. 3

Fig. 3 Wild-type expression at 24 h postfertilisation. Transcripts were revealed by in situ hybridisation with antisense RNA probes to ptc1 (A, E, H, and I), ptc2 (B, C, D, G, and J), and shh (F) and slow muscle fiber types were detected by immunolocalisation with the BA-D5 antibody (K). All embryos were fixed at 24 hpf. (A and B) Expression in the hindbrain. There are six vertical stripes of ptc2 expression which mark the boundaries of rhombomeres 2–6 ((B) shown with black arrows). This rhombomeric expression of ptc2 is similar, but not identical, to the expression of ptc1 (A), which is elevated in rhombomeres 2 and 4 (rectangular brackets) and the edges of rhombomere 6 (black arrows). The expression of ptc1 and ptc2 differs considerably in the somites; ptc1 is expressed only in the presomitic and somitic mesodermal cells that are adjacent to the notochord, whereas ptc2 has a dynamic pattern of expression along the rostrocaudal axis which is very similar to that of BA-D5 which marks slow muscle fiber types (G–J and cf. K). (C–F) were obtained by embedding embryos in wax and sectioning them after the in situ hybridisation procedure. The black arrows point to the floor plate, the red dashed lines demarcate the ventral edge of the neural tube, and nc denotes notochord. Neither ptc1 nor ptc2 is expressed in the rostral floor plate (C–E), though both are still expressed in the floor plate in the tail (data not shown). The neural tube expression of ptc2 is slightly stronger than the somite expression as revealed by the specimen in (C), which was stained for a shorter time than that in (D): (C) shows ptc2 expression throughout the neural tube except for the floor plate while (D) shows ptc2 expression in the neural tube and throughout the somites. ptc1 expression is much more restricted than ptc2; it is expressed only in the ventral neural tube (apart from the floor plate) and the medial somite (E). Neither ptc gene is expressed in the notochord. (F) Caudal section where shh is still expressed in the notochord, in addition to being expressed in the floor plate.