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The biochemical composition and biosynthetic activity of Xenopus notochord were examined and compared with those of chick and mouse notochord. The notochords of all three species contain type-II collagen, and the notochords of Xenopus and chick synthesize a soluble glycoprotein with a molecular mass of 86 kilodaltons (kd). Mouse embryos were not tested for this molecule, because their notochords are too small to be dissected out. Most interestingly, Xenopus and chick notochords share a keratan-sulphate-containing proteoglycan which appears to be absent from mouse notochord. The presence or absence of keratan sulphate in the notochords of the different species reflects its presence or absence in cartilage. Since one role of the notochord in vivo is to stimulate chondrogenesis in the sclerotomes of the somites, this result provides support for the view that cells responding to the extracellular matrix produced by one tissue do so by increasing their production of the same matrix components.
Fig. 1. Glycoprotein synthesis by diffcrent regions of Xenopus ncurulac
analysed by SDS-polyacrylamide gradient gel electrophorcsis
and fluorography. In trucks 1-7, the explants were Iabellcd with
'H-mannose. Track 1, neural plate; truck 2, epidermis; rrack 3,
notochord; track 4, dorsal mesoderm; rrack 5, ventrolateral mesoderm;
truck 6, yolk mass; truck 7, whole embryo. Track 8 is a
notochord explant labelled with "S-mcthionine. Molecular-mass
markers are shown ( x 10-j)
Fig. 3A-F. Keratan sulphate in notochords of stage-27 Xcnopw
(A, B) stage-18 chick (C, D) and 10.5day T/O mouse (E, F) visualized
by indirect immunofluoresccnce with the monoclonal antibody
MZ15. A, C, E Phase contrast; B, D, E MZ15 immunofluorescence.
Keratan sulphate is present in Xcnopus and chick but not in mouse
notochords. Bur, 50 pm (applies to all figures)
Fig. 4A-D. Keratan sulphate in mature Xenopus cornea (A, B)
and stage-56 limb-bud cartilage (C, D). A, C Phase contrast: B,
D MZ15 immunofluorescence. Bur, 50 pm (applies to all figures)
Fig. 5A-H. Keratan sulphate distribution at different stages of development
in Xenopus. A, B Stage 16; C, D stage 20; E, F stage
44; G, H stage 56. A, C, E, G Phase contrast; B, D, F, H MZ15
immunofluorescence. Staining of the notochord is not visible at
stage 16, but is clear at stages 20 and 44. At stage 56, staining
in the notochord has disappeared, but the vertebral cartilage is
positive. Bars, 50 pm
Fig. 6A-F. Type-I1 collagen in chick (stage 18; A, B) Xenopus
(stage 27; C, D) and mouse (T/O, 12.5 days; E, F) notochords.
A, C, E Phase contrast; B, D, F immunofluorescence using antibodies
against type-I1 collagen. Note positive staining of mouse
cartilage in F. Bar, 50 pm (applies to all figures)
