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Syndecans are a family of heparan sulfate proteoglycans implicated in cell-cell and cell-matrix interactions. To investigate the roles of syndecans in early development, we identified three syndecan family members in Xenopus laevis: Xsyn-1, Xsyn-2, and Xsyn-3. Xsyn-1 and Xsyn-2 are maternal mRNAs localized to the animal pole in blastulae, and are expressed in the ectoderm of gastrulae. In neurulae, Xsyn-1 is restricted to non-neural ectoderm and Xsyn-2 is restricted to neural ectoderm. In tailbud embryos, the three syndecans are expressed in adjacent, non-overlapping patterns. Xsyn-2 is expressed in the heart while Xsyn-1 is expressed in the underlying anterior endoderm. Xsyn-3 is expressed in the hindbrain, midbrain, and forebrain, while Xsyn-2 is expressed in the intervening regions. These results suggest that different members of the syndecan family have distinct developmental roles, perhaps acting as barriers to define tissue boundaries.
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Fig. 4. In situ analysis of Xsyn-I RNA expression during development. (A) Animal view of blastula stage embryo (stage 7), showing Xryn-1 mRNA present in the animal hemisphere. (B) Animal-vegetal section of blastula stage embryo, indicating that Xsyn-I is localized to the animal pole of the embryo. Animal pole is to the top. (C) Animal view of an early gastrula (stage 10). Dorsal is to the top. Xsyn-I mRNA is still present in the animal pole. (D) Animal-vegetal section of a midgastrula (stage 11.5). Animal pole is to the top. Xryn-l is expressed in the inner sensorial layer of the ecto- derm, and is absent from vegetal cells and cells which have ingressed through the blastopore lip. Arrowheads denote boundaries of Xsyn-1 expression at the blastopore lip. (E) Lateral view of an early neurula (stage 13); this embryo is not cleared so only surface staining is visible. Dorsal is to the top, anterior is to the right. Xsyn-1 expression is absent from the neural plate and is limited to a band of ectoderm around the embryo. Expression is highest in the posteriorectoderm. nb, boundary of the neural plate. (F) Lateral view of midneurula (stage 15). Dorsal is to the top, anterior is to the right. Xsyn- 1 expression is restricted to a patch of posteriorectoderm and to a patch of anteriorectoderm corresponding to the future cement gland (cg). (G) Ven- tral view of late neurula (stage 20). Anterior is to the right. Xryn-I expression is present in the cement gland (cg) and a small patch of posterior ecto- derm. (H) Lateral view of late tailbud stage embryo (stage 40). Anterior is to the right. High levels of Xsyn-I expression are seen in the anterior endo- derm (ae) and in the cement gland (cg). Xsyn-1 expression is also seen in the phalyngeal mesoderm, and at low levels throughout the epidermis. (I) Stage 40 sense control. Faint background staining is seen in the anterior of the embryo. Sense controls for all other stages showed no background, Bars, 0.5 mm. Bar in (A) applies to (B-F),
Fig. 5. In situ analysis of Xsyn-2 RNA expression during development. (A) Lateral view of blastula (stage 7); animal pole is to the top, Xsyn-2 is ex- pressed in the animal hemisphere, the future ectoderm. (B) Animal-vegetal section of blastula stage embryo, confirming localization of Xsyn-2 mRNA to the animal hemisphere. Animal is to the top. (C) Animal-vegetal section of a midgastrula embryo (stage 11.5) showing Xsyn-2 expression in the sensorial layer of the ectoderm. Arrowheads denote the boundaries of Xsyn-2 expression at the blastopore lip. Animal pole is to the top. (D) Lateral view of early neurula (stage 13); anterior is to the tight, dorsal is to the top. This embryo is not cleared, so only surface staining is visible. Xsyn-2 ex- pression is now restricted to the neural plate, and is not found in lateral or ventralectoderm. nb, neural plate boundary. (E) Dorsal view of midneurula (stage 15); anterior is to the right. Xsyn-2 expression is restricted to the neural midline (nm) and to the anterior neural folds. (F) Lateral view of early tailbud stage embryo (stage 28): anterior is to the right, dorsal is to the top. Xsyn-2 is expressed at relatively high levels in the midbrain-hindbrain and midbrain-forebrain boundaries (arrowheads), and in the otic vesicles (ot). Lower levels of expression are seen in the floorplate of the neural tube, eye, tailbud. somites, pharyngeal mesoderm, pronephros and pronephric duct. (G) Lateral view of mid-taiibud stage embryo (stage 33); anterior is to the right, dorsal is to the top. This embryo was overstained to show Xsyn-2 expression in the heart (h). The cardiac tube is justeginning to loop at this stage. (H) Stage 33 sense control. This embryo was overstained as in (Cl). Faint background is present in the brain and pharyngeal mesoderm. Sense controls for all other stages had no background. Bars, 0.5 mm. Bar in (A) applies to (B-E,G.H).
Fig. 6. Expression of Xsyn-2 in the floor plate of the neural tube. In situ-hybridized stage 33 embryos were embedded in paraplast and 35um traneverse sections were cut. Dorsal is up. (A) Antisense-hybridized embryo. Xsyn-2 is expressed in the floor plate of the neural tube (closed arrow). (B) Sense control, showing no staining in the floor plate (open arrow). Background staining is visible in the dorsal lumenal surface of the neural tube. nt, neural tube; no, notochord. Bar, 0.05 mm.
Fig. 7. In situ analysts of Xsyn-3 expression during development. (A) Lateral view of mid-tailbud stage embryo (stage 33); anterior is to the right, dorsal is to the top. Xsyn-3 is strongly expressed in the entire brain, except for the midbrain-hindbrain and midbrain-forebrain boundaries (arrowheads). Xsyn-3 is also expressed m the pharyngeal mesoderm. (B) Sense control. Faint background is present in the brain. Bar, 0.5 mm.
Fig. 3. Northern blot analysis of Xsyn-1 and Xsyn-2 expression during development. (A) Developmental Northern blot probed with Xsyn-I cDNA. Numbers across the top represent Xenopus developmental stages. The high molecular weight band has resolved on other blots as a doublet of 5.9 and 5.3 kb; the smaller RNA species is 2.6 kb. The RNA species are present at their highest levels in blastula and gastrula stages (3-12) at their lowest levels in neurula and early tailbud stages (15- 28), and at intermediate levels in late tailbud and tadpole stages (30- 47). (B) The same Northern blot was probed with Xsyn-2 cDNA. A major band of 3.6 kb and a minor band of 1.8 kb are observed. Abun- dance of both RNA species is lowest in blastula stages (2-7), higher in gastrula through early tailbud stages (lO-28), and highest in late tailbud and tadpole stages (30-47). (C) The same Northern blot was probed with Xenopus 18s ribosomal DNA as a control for the amount of RNA loaded in each lane.
