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We have cloned and characterized a Xenopus member of the cyclase associated protein (CAP) gene family. xCAP1 is expressed as a maternal transcript, but is up-regulated prior to gastrulation and subsequently localizes to headmesenchyme, lens, otic vesicle, and trunkmesoderm including the pronephros. At different stages, the gene also appears to differentiate surface from deep (sensorial) ectoderm. As in Drosophila, Xenopus CAP1 is expressed in the developing eye, specifically in the differentiating lens. However, in distinction to Drosophila, Xenopus CAP1 does not express in periodically arrayed neural bands.
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11960715
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Fig. 2. xCAP1 expression during embryogenesis. Maternal xCAP1 transcript becomes localized to the animal pole during the early stages of cleavage (A), and progressively concentrates on the presumptive dorsal (d) side (A,B). As the ectoderm thickens, surface ectoderm down-regulates xCAP1 at the extreme animal pole, while expression ensues in sensorial ectoderm, marginal zone and dorsal mesoderm during gastrulation, so that cells immediately above and passing through the dorsal lip (dl) express (C). Late in gastrulation, presumptive neurectoderm is devoid of xCAP1 expression anteriorly (not shown), but by mid neurulation, the gene expresses in neurectoderm up until the neural folds have sutured. Both layers of dorsal ectoderm express during neurulation, as well as dorsal mesoderm and neurectoderm. Dorsal expression extends in a comparable pattern from the yolk plug to the anterior end (a), but is absent from endoderm from neural plate (stage 12) through to neural tube suturing (in this dorsal view of a stage 15.5 embryo)(D). During elaboration of the head, xCAP1 is expressed in the branchial arches (ba), otic vesicle (o), lens (l), and peri-optic mesenchyme (pom) (E,F). Branchial arch expression is predominantly mesenchymal. By stages 36–37, olfactory placodes (op) and pronephric structures (pn) express transcript (G,H).
Fig. 3. xCAP1 expression revealed in section. Animal pole (an) and surface ectoderm (se) do not express xCAP1 during gastrulation, though both mesoderm (m) and sensorial ectoderm (sn) do (A). Cells passing through the dorsal lip (dl) appear to temporarily down-regulate xCAP1 indicating that expression patterns of this transcript can be rapidly altered. By late neurulation (B), both layers of ectoderm express transcript, but expression in surface ectoderm begins to diminish, while sensorial ectoderm (sn) and, to a lesser extent lateral plate mesoderm (lpm) continue to express. Neither notochord (n) nor somites (s) express xCAP1, however, a low level of expression can be seen in the lateralventral aspect of the neural tube (nt). During tail bud stages (C), transcript is detectable in the ventralrhombencephalon (r), the otic vesicle (o), and the lateral plate mesoderm (lpm), and expression in surface ectoderm has down-regulated. When eye begins to form, xCAP1 expression is detectable in the lens, particularly at the margins (D). By this stage xCAP1 expression is entirely lacking in the surface ectoderm.
