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#transplantation

3 public questions tagged with this topic.

Specification Determination-l

What happens if a specified but not determined cell is transplanted into another region of an embryo?

A cell that is specified but not yet determined retains considerable responsiveness to environmental cues. When heterotopically transplanted into a different embryonic region, surrounding inductive signals such as BMP antagonists, Wnt ligands, FGFs or Notch ligands can overwrite initial bias and respecify fate to match host location, reflecting open chromatin and continued receptor expression. This plasticity distinguishes specification as labile phase. Once determination occurs, epigenetic barriers including DNA methylation and Polycomb-mediated repression, plus autoregulatory transcription loops, prevent redirection, causing cells to differentiate according to origin regardless of new surroundings, revealing transition to stabilized commitment.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 5: Lability of Specified Cells Upon Transplantation.

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Sea Urchin -ll

Transplanting micromeres to the animal hemisphere induces:

Micromeres function as embryonic organizer in sea urchins comparable to amphibian dorsal lip. Horstadius in 1935 demonstrated transplanting fluorescently labeled micromeres from 16-cell embryo to animal pole of otherwise intact host embryo causes adjacent animal cells, normally fated to ectoderm, to change destiny, invaginate and form second archenteron with associated pigment cells and secondary mesenchyme. Induction requires Delta-Notch juxtacrine presentation and Wnt8 plus early β-catenin paracrine signals that reprogram host ectoderm toward endomesoderm. Resulting twinned gastrulation mimics Spemann organizer experiment. Transplant thus induces secondary archenteron formation, proving conditional specification of animal hemisphere under micromere influence.

Ref: Hörstadius 1935 organizer experiment; Gilbert, Developmental Biology, Chapter 8: Micromere transplantation and induction.

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chick development-l

Hensen’s node transplantation experiments result in:

Classic organizer experiment by Waddington grafted Hensen's node from donor chick embryo into lateral area pellucida of host embryo. Donor node retained autonomy expressing Chordin, Noggin, Shh and Goosecoid, antagonizing BMP in surrounding host epiblast inducing ectopic neural plate marked Sox2 and ectopic notochord. Host developed secondary embryonic axis complete with somites and neural tube parallel to primary axis. Result proved avian node equivalent to Spemann organizer, capable of neural induction and dorsal mesoderm patterning, demonstrating conserved mechanism of secondary axis induction via BMP antagonism across vertebrates.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Hensen's node transplantation inducing secondary embryonic axis.

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