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Developmental basis of limblessness and axial patterning in snakes
1Division of Zoology, School of Animal and Microbial Sciences, University of Reading, UK. M.J.Cohn@reading.ac.uk
Nature
|June 12, 1999
Summary
Snake evolution involved significant body plan changes, but their developmental origins were unclear. Hox gene expansion in python embryos explains limb loss and trunk elongation, revealing a key evolutionary mechanism.
Area of Science:
- Developmental biology
- Evolutionary biology
- Comparative anatomy
Background:
- Snake evolution is characterized by major vertebrate body plan alterations, including limb loss and trunk elongation.
- The developmental underpinnings of these evolutionary changes in snakes remain largely unknown.
- Combined limb loss and trunk elongation suggest a shared developmental mechanism across taxa.
Purpose of the Study:
- To investigate the developmental basis of snake-specific body plan modifications in python embryos.
- To determine the role of Hox gene expression in the absence of forelimbs and hindlimb reduction.
- To explore the signaling pathways involved in python limb development and potential rescue mechanisms.
Main Methods:
- Analysis of Hox gene expression patterns in python embryos along the anterior-posterior axis.
- Investigation of hindlimb bud initiation and the activation of key limb signaling pathways (apical ridge, polarizing region).
- Experimental manipulation using fibroblast growth factor (FGF) and chick apical ridge recombination to assess rescue of python limb development.
Main Results:
- Expanded Hox gene expression domains were observed along the python body axis.
- This Hox gene expansion correlates with the absence of forelimbs and the increased thoracic vertebral identity.
- Python hindlimb buds initiate but fail to develop due to lack of apical ridge and polarizing region signaling.
- Limb bud outgrowth and Sonic hedgehog signaling in pythons can be rescued by FGF or chick apical ridge.
Conclusions:
- Altered Hox gene expression during python embryogenesis is a primary driver for both forelimb loss and axial skeleton elongation.
- The failure of limb bud development in pythons is linked to the dysregulation of critical limb signaling pathways.
- These developmental changes, potentially originating from early shifts in Hox gene regulation, provide insight into the evolution of the snake body plan.
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