Fig. 6. Brachyury is expressed at skeletal sites during late murine embryonic development (18.5 d.p.c.). Comparative expression analysis of murine Brachyury (Bra), Collagen 1a1 (Col 1a1) and Collagen 2a1 (Col 2a1) in embryonic development 18.5 d.p.c. (A) Intervertebral disc development. Consecutive sagittal (a-g) and transverse (h-j) sections of 18.5 d.p.c. mouse embryos were hybridized with riboprobes as indicated. Expression of Brachyury is enhanced in the nucleus pulposus (np) (a,d), Col 1a1 in the outer annulus (oa) (arrowheads in b,e), and Col 2a1 in the cartilage primordium (cp) of the vertebrae (c,f). No signals were obtained using RNase pre-incubated sections (g). With transverse sections at the level of the upper lumbar vertebra, expression of Brachyury is also detectable in distinct cells of the neural arch (h), whereas Col 1a1 is expressed in the outer annulus (i) and Col 2a1 in the cartilage primordium (j). (B) Limb bud development. Consecutive transverse sections of an 18.5 d.p.c. mouse hind limb at the level of the metatarsals, hybridized with riboprobes as indicated. Expression of Brachyury is evident in distinct chondrogenic cells of the forming metatarsal bones (a), better visible at higher magnification (b,c). In contrast Col 1a1 is expressed in the outer periosteal layer (d-f) and Col 2a1 expression is enhanced in differentiating chondrocytes (g-i). As was evident for the intervertebral disc formation, expression of Brachyury is only seen in chondrocyte-like cells that do not express Col 2a1. Bar, 100 µm.

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