Fibroblast Growth Factor (FGF) signaling plays essential roles in vertebrate embryogenesis, including the induction and patterning of mesodermal tissues that contribute to trunk and tail formation. In amphibians such as Xenopus, perturbation of FGF signaling—particularly by overexpressing a dominant negative (dn) FGF receptor—disrupts these processes and blocks normal development of posterior structures.

Role of FGF and FGFR in Amphibian Development

• FGF signaling is a critical inducer of mesoderm formation, which gives rise to major body structures including trunk and tail.

• The FGF receptors, notably FGFR1 and FGFR2 in Xenopus, mediate this signaling by activating downstream pathways such as MAPK/ERK that regulate gene expression during gastrulation.

• Interference with FGFR function by dominant negative receptors blocks FGF signaling, leading to failure in mesoderm induction and maintenance, severely affecting posterior body development.

Effects of Dominant Negative FGF Receptor Overexpression

• Experimental overexpression of a dominant negative FGFR in amphibian embryos prevents the formation of trunk and tail structures, as these regions depend heavily on FGF-mediated mesoderm specification and elongation.

• The head region is typically less affected, as its early induction relies more on other signaling pathways and maternal determinants.

• Similarly, limb buds, particularly forelimbs, may not form properly if mesoderm development is disrupted, but the critical direct effect is on trunk and tail axis establishment.

Why Other Options Are Less Consistent

• Head and trunks (option 2): Head development is often less sensitive to FGF signaling blockade than trunk and tail.

• Trunk and forelimbs (option 3): Forelimb field establishment also depends on more complex signals beyond FGF alone, and damage to trunk and tail formation is more pronounced.

• Head and forelimbs (option 4): Similar to above, these regions rely on additional factors and are not as critically blocked by dnFGFR as trunk and tail.

Conclusion

The overexpression of a dominant negative Fibroblast Growth Factor receptor in amphibian embryos primarily disrupts trunk and tail formation. This reflects the indispensable role of FGF signaling in mesoderm induction, posterior axis elongation, and patterning during critical phases of early development.

The correct answer is:
(1) trunk and tail