- Hensenis node is established as the avian equivalent of the amphibian dorsal blastopore lip. The following observations are presumed to be support of the same.
A. It is the region whose cells induce and pattern a second embryonic axis when transplanted into other locations of the gastrula.
B. It is equivalent in terms of tissue structure.
C. It expresses the same marker genes as the Spemann’s organizer in Amphibians.
D. The same micro RNA can interfere with the formation of pre-chordal plate in both Hensen’s
node and Spemann’s organizer.
Choose the correct set among the following:
(1) A and D (2) A and C
(3) B and C (4) A and B
Hensen’s node is widely recognized as the avian equivalent of the amphibian dorsal blastopore lip (the Spemann organizer). The correct supporting observations are:
A. It is the region whose cells induce and pattern a second embryonic axis when transplanted into other locations of the gastrula.
C. It expresses many of the same marker genes as the Spemann organizer in amphibians, such as goosecoid and chordin.
Statements B (equivalence in tissue structure) and D (same micro RNA interference in pre-chordal plate formation) are less definitively supported or nuanced in literature.
Therefore, the correct combination is (2) A and C.
Introduction
In vertebrate embryology, the Spemann organizer in amphibians and Hensen’s node in birds represent critical signaling centers responsible for embryo patterning and axis formation. Hensen’s node located at the anterior end of the primitive streak shares functional and molecular characteristics with the amphibian dorsal blastopore lip, guiding development through cell signaling and gene expression that patterns the embryonic axis.
Induction of a Secondary Axis by Hensen’s Node
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Like the Spemann organizer, cells from Hensen’s node can induce and pattern a secondary embryonic axis when transplanted ectopically into gastrula-stage embryos.
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This functional demonstration confirms Hensen’s node as the avian organizer responsible for axial patterning.
Shared Genetic Markers with Spemann Organizer
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Hensen’s node expresses key transcription factors and genes integral to organizer function, including goosecoid (gsc), chordin, and noggin.
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These markers are well conserved across species and signify organizer identity and signaling potency.
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Genetic and transcriptomic studies reveal strong overlap in molecular signatures between Hensen’s node and amphibian organizer, supporting a deep evolutionary homology.
Structural Equivalence and Micro RNA Regulation
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While structurally both organizers serve similar inductive roles, they arise in differing embryonic morphologies reflecting differences between amphibians and birds (diffuse blastula vs. flat blastodisc).
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Emerging studies suggest certain microRNAs modulate organizer function and pre-chordal plate development across vertebrates, including both Hensen’s node and Spemann organizer; however, mechanistic details remain nuanced and less definitive than genetic marker and functional equivalences.
Summary Table: Comparison of Hensen’s Node and Spemann Organizer
| Aspect | Hensen’s Node (Birds) | Spemann Organizer (Amphibians) | Supported by Literature |
|---|---|---|---|
| Function | Induces and patterns secondary embryonic axis | Same | Yes; transplantation experiments |
| Genetic Markers | Expresses goosecoid, chordin, noggin | Same genes expressed | Yes; molecular studies confirm |
| Tissue Structure | Primitive node at primitive streak tip | Dorsal lip of blastopore | Partially; embryonic morphology differs |
| Micro RNA Role in Pre-Chordal Plate | Micro RNA interference observed but complex | Possibly similar mechanisms | Less definitive; ongoing research |
Conclusion
Hensen’s node is functionally and molecularly homologous to the amphibian Spemann organizer, as evidenced by its ability to induce a secondary embryonic axis and shared expression of key organizer genes like goosecoid. Thus, statements A and C best support the equivalence of these two developmental organizers.
FAQ
Q: What is Hensen’s node in chick embryos?
It is the organizer region that induces body axis formation, equivalent to the amphibian dorsal blastopore lip.
Q: Does Hensen’s node express the same genes as the Spemann organizer?
Yes, it expresses conserved organizer genes such as goosecoid and chordin.
Q: Can cells from Hensen’s node induce a second embryonic axis?
Yes, transplantation experiments demonstrate its ability to induce and pattern a secondary axis.
Understanding Hensen’s node as the avian counterpart to the amphibian organizer deepens insight into conserved vertebrate developmental mechanisms, essential for embryology and evolutionary biology studies
