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Appendages and gene regulatory networks: Lessons from the limbless
Carlos R Infante1, Ashley M Rasys2,3, Douglas B Menke3
1Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, 85721.
Genesis (New York, N.Y. : 2000)
|October 28, 2017
Summary
Snake genomes retain ancient limb enhancers, but functional tests reveal they now primarily regulate external genitalia development, not limbs. This suggests gene regulatory networks for limbs and genitalia may constrain appendage evolution.
Area of Science:
- Evolutionary developmental biology
- Comparative genomics
- Vertebrate limb development
Background:
- Limb reduction has evolved independently in numerous squamate reptile lineages, offering natural experiments for studying vertebrate limb evolution.
- Snakes, a well-known example of limb reduction, evolved their body form over 100 million years ago.
- Previous research identified conserved limb enhancers in snake genomes, hinting at their retained functionality.
Purpose of the Study:
- To investigate the functional fate of ancient limb enhancers in snakes, a limb-reduced lineage.
- To test the hypothesis that conserved limb enhancers were retained in snakes due to their role in external genitalia development.
- To explore the implications of overlapping gene regulatory networks in limb and phallus development for appendage evolution.
Main Methods:
- Comparative genomic analysis to identify conserved limb enhancers in snake genomes.
- In silico analyses to determine the activity of these enhancers during development in limbed animals, particularly in the phallus.
- Functional testing of snake enhancer elements to assess their activity in limb versus genital development.
Main Results:
- Many ancient limb enhancers are conserved in snake genomes.
- These enhancers are active during phallus development in limbed animals, supporting their potential retention in snakes for genital regulation.
- Functional tests confirmed that snake enhancers have lost limb function but retained genital enhancer function.
Conclusions:
- Conserved limb enhancers in snakes have been repurposed for external genitalia development, indicating functional shifts in gene regulatory networks.
- The overlap between limb and phallus gene regulatory networks may constrain the evolution of appendage morphology.
- Further research is needed to determine if similar functional changes occurred in other limb-reduced squamate lineages.
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