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We have isolated the Xenopus ortholog of ADAMTS1 (a disintegrin and metalloprotease with thrombospondin motifs), XADAMTS1, which is expressed in the presumptive ectoderm, then the Spemann organizer, and later in the trunkorganizer region and posteriorectoderm in the Xenopus embryo. We show that, when overexpressed in the dorsal marginal zone or in the anteriorectoderm by mRNA injection, XADAMTS1 inhibits gastrulation or generates embryos with an enlarged cement gland, respectively. XADAMTS1 also reduces the expression of Xbra in both whole embryos and FGF-treated animal caps. These effects of XADAMTS1 are likely to be due to its inhibition of the Ras-MAPK cascade because XADAMTS1 inhibits the phosphorylation of ERK by FGF4 in animal caps. Deletion analysis of XADAMTS1 revealed that a combination of the signal peptide and the C-terminal region containing the thrombospondin type 1 repeats is necessary and sufficient for this function, whereas the metalloprotease domain is dispensable. In addition, loss-of-function analysis with antisense morpholino oligos showed that knockdown of XADAMTS1 sensitizes animal caps to Xbra induction by FGF2. These data suggest that secreted XADAMTS1 negatively modulates FGF signaling in the Xenopus embryo.
Fig. 2. Analysis of XADAMTS1 expression. (A) Northern blot analysis. Total RNA (10 μg) from different developmental stages was loaded in each lane. Bands of 18S rRNA stained with ethidium bromide were used for a loading control. (B) Whole-mount in situ hybridization for XADAMTS1 mRNA during blastula to neurula stages. (a, b) Late blastulae (stage 8.5) bisected vertically after staining for XADAMTS1 (a) and FGF8 (b). Magnified images of the enclosed regions are shown in the inset. (c) Comparison of expression domains between XADAMTS1 and Xlim-1 at the gastrula stage (stage 10.5). Embryos were bisected into left and right halves and subjected to whole-mount in situ hybridization for XADAMTS1 (left panel) and Xlim-1 (right panel), respectively. Dorsal is to the right (XADAMTS1) or the left (Xlim-1). (d) Vegetal view of a mid-gastrula embryo (stage 11.5) cleared with BB/BA. (e–g) Late gastrulae (stage 12) bisected sagittally after staining for XADAMTS1 (e), FGF4 (f), and FGF8 (g). Dorsal is upwards; anterior is to the left. (h) Dorsal view of neurula (stage 18). Anterior is upwards. (C) Expression patterns of XADAMTS1 at tailbud stages. (a) Early tailbud stage embryo (stage 26). Transverse (b–d) and horizontal (e) sections of stained tailbud stage embryos (stage 26). (f) Late tailbud stage embryo (stage 31) cleared with BB/BA. (g) Transverse section of a stained late tailbud stage embryo (stage 31). Dorsal is upwards (a–d, f, g). Anterior is to the left (a, e, f). ba, branchial arch; d, dermatome; e, eye; h, heart anlage; n, notochord; nt, neural tube; ov, otic vesicle; pn, pronephros. Arrowheads indicate the dorsal blastopore.
adamts1 <ADAM metallopeptidase with thrombospondin type 1 motif, 1 > expression in Xenopus laevis, stage 31 embryo, laterla view, anterior left.
Source: Suga A, Hikasa H, Taira M., Dev Biol. July 1, 2006; 295 (1): 26-39
Pubmed Id: 16690049