Fig. 2

Joint cells and osteoblasts originate from a common cell lineage, but are later committed to different cell fates. All panels show ISH and FISH data for various markers on longitudinal cryosections of 4 dpa fin regenerates except E′, which shows mCherry reporter expression. (A,B) runx2a and runx2b expression domains form a ‘bump’ at the joint-forming cell cluster (blue arrowheads). (C,D) Absence of sp7 (C) and col10a1a (D) expression in the joint cell cluster (blue arrowheads). (E) The distal limit of the domain of expression of the late osteoblast marker bglap (black arrowhead) is proximal to the location of the joint-forming cells (approximate location indicated by blue arrowhead). (E′) mCherry reporter expression in Tg(bglap:mCherry) fish is absent in the distal regenerate (dark blue arrowhead), joints of the regenerate (yellow arrowhead), and mature joints in the stump (light blue arrowhead). Dashed line indicates the amputation plane. (F,F′) ihha is not expressed in the joint-forming cells (blue arrowheads). (G) In contrast, pthlha is expressed in the joint-forming cells (blue arrowhead). (H-O) Double FISH confirms pthlha expression in joint-forming cell clusters (blue arrowheads) that do not express ihha but do express ptch2 (blue arrowheads). I, J and K show magnifications of the boxed area in H. M, N and O show magnifications of the boxed area in L. Scale bars: 100 μm (E; in A for A-D,F,G); 200 μm (E′); 10 μm (F′; in I for I-K; in M for M-O); 50 μm (H,L).