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The evolution of arthropod segmentation mechanisms.
1University Museum of Zoology, Downing Street, Cambridge CB2 3EJ, UK. apd32@cam.ac.uk
Summary
Fruit flies use diffusing transcription factors for rapid, simultaneous segmentation. This contrasts with ancestral arthropods, suggesting an evolutionary shift from sequential to simultaneous patterning mechanisms.
Area of Science:
- Developmental biology
- Evolutionary biology
- Genetics
Background:
- Fruit flies (Drosophila melanogaster) exhibit rapid, simultaneous segmentation via nuclear transcription factor diffusion.
- Ancestral arthropods likely used sequential segmentation in a cellular environment, with diffusion possibly limited by cell membranes.
Purpose of the Study:
- To review arthropod segmentation mechanisms.
- To propose a model for the evolution of the Drosophila segmentation paradigm.
Main Methods:
- Review of existing literature on arthropod segmentation.
- Development of a theoretical model for evolutionary changes in segmentation.
Main Results:
- The model predicts ancestral pair-rule genes functioned with a Notch-dependent segmentation clock.
- Striped gene expression shifted to be controlled by gap genes as simultaneous anterior patterning increased and sequential posterior patterning decreased.
Conclusions:
- The evolution of Drosophila segmentation involved a transition from sequential to simultaneous patterning.
- This transition is linked to changes in gene regulation, with gap genes gaining control over pair-rule gene expression.