Fig. 1. Expression of Mkp3 during chick somite development correlates with the expression of scleraxis in somites and with the expression of Fgf4 and Fgf8 in myotomes. (A-C,G-L) Whole-mount in situ hybridisation of HH15, HH19, HH20 and HH23 chick embryos. (A,J) Mkp3. (J) Hind-limb buds were removed to show expression in posterior somites. (B,K) scleraxis, blue asterisk indicates the axial level of expression in somites, red arrow indicates scleraxis expression in presegmented mesoderm; (C,L) spry2; (G) Fgf4; (H) Fgf8; and (I) FGFR4/FREK. (D-F) Frontal sections through HH24 somites stained with MF20 antibody to visualise myosin heavy chain protein in the myotome (green) together with (D) Mkp3 transcripts (dark purple) in the dorsal sclerotome along the anterior and posterior somite edges. (E) MF20 and scleraxis transcripts (red). (F) MF20 and spry2. Brackets in J,G indicate the triangular shaped expression in posterior somites. ba, branchial arches; dm, dermomyotome; is, isthmus; lb, limb bud; my, myotome; ol, olfactory epithelium; op, optic vesicle; ot, otic vesicle; s, somite; sc, sclerotome; tb, tail bud.