#dorsal lip

amphibian Development-l

Which cells form the dorsal lip of the blastopore?

During amphibian gastrulation, marginal zone cells at dorsal side undergo actin-myosin mediated apical constriction, accumulating F-actin and phosphorylated myosin apically and shrinking outer surface while expanding basally. These flask-shaped bottle cells invaginate inward, pulling adjacent epithelium and creating initial blastopore pit that becomes dorsal lip of blastopore. Bottle cell constriction initiates involution of chordamesoderm and marks Spemann organizer region secreting BMP antagonists like chordin and noggin, essential for axial patterning, archenteron formation, and internalization of dorsal mesoderm during early development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Gastrulation bottle cells and dorsal blastopore lip.

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amphibian -ll

Transplanting dorsal lip tissue into a ventral region causes:

Spemann and Mangold transplanted dorsal lip of blastopore containing prospective chordamesoderm, which normally involutes as notochord, into ventral marginal zone of host gastrula opposite side. Donor tissue retained organizer program expressing Chordin and Noggin, antagonizing ventral BMP4 and eliciting host ventral ectoderm to form secondary neural plate marked Sox2. Host also contributed somites around graft forming second axis. Resulting conjoined twins with secondary dorsal axis bearing notochord and neural tube demonstrated induction not self-differentiation alone. No ventralization occurs; secondary embryo formation proves organizer instructive capacity and neural induction capability.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Transplantation of dorsal lip causing secondary embryo formation.

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amphibian -ll

The dorsal lip of the blastopore forms due to:

After cortical rotation, vegetal endoderm undergoes vegetal rotation where large yolky dorsal marginal cells move inward and upward, forming wedge thrust pushing dorsal marginal mesoderm outward creating lip. This movement of bottle cells and involution starts at gray crescent region, generating dorsal blastopore lip visible as pigment-free arc. Rotation driven by Brachyury and Wnt11 dependent cell intercalation and apical constriction via Shroom3. Animal pole elongation not involved. Process establishes site of gastrulation and marks organizer region preparing for mesoderm involution and archenteron formation during amphibian gastrulation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Vegetal rotation and formation of dorsal blastopore lip.

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amphibian -ll

Spemann's organizer is derived from:

Gray crescent cytoplasm contains determinants accumulated via cortical rotation: dishevelled protein, GBP, kinesins and Wnt11 RNA enriched dorsally inhibiting GSK-3 beta. This permits beta-catenin nuclear accumulation in dorsal marginal cells overlaying crescent. These cells become Spemann organizer in dorsal blastopore lip expressing Goosecoid, Chordin and Noggin, inducing neural plate. Transplantation shows dorsal equatorial region derived from gray crescent involutes as chordamesoderm. Ventral blastopore cells lacking nuclear beta-catenin form blood and mesenchyme, not organizer activity, confirming developmental origin from gray crescent.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Spemann organizer derived from gray crescent equatorial region.

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