Genomic Takeover by Transposable Elements in the Strawberry Poison Frog

Area of Science:

• Genomics
• Evolutionary Biology
• Molecular Biology

Background:

• Amphibian genome sizes vary significantly.
• Transposable elements (TEs) contribute to genome size variation.
• Poison frogs possess unique adaptations, such as toxin sequestration.

Purpose of the Study:

• To sequence and analyze the genome of the strawberry poison frog (Oophaga pumilio).
• To investigate the role of transposable elements in genome expansion.
• To explore the evolutionary basis of toxin resistance in poison frogs.

Main Methods:

• Whole-genome sequencing of Oophaga pumilio using variable insert size libraries.
• Bioinformatic analysis of repetitive elements, including DNA transposons, RNA transposons, and LTR retrotransposons.
• Phylogenetic analysis to detect horizontal gene transfer (HT).
• Gene expression analysis in ova.

Main Results:

• The O. pumilio genome is estimated at 6.76 Gb, with 4.76 Gb composed of repetitive elements, notably Mariner/Tc1 and Gypsy elements.
• High expression of Gypsy and Mariner/Tc1 elements was observed in ova.
• Evidence for horizontal transfer of Mariner elements between fish and frogs was found, with these elements showing high copy number and expression.
• Changes in the spliceosome and identification of ion channels related to toxin resistance were noted.

Conclusions:

• Repeated invasion and proliferation of transposable elements, particularly after horizontal transfer, contribute significantly to large amphibian genome sizes.
• The spliceosome may be permissive to increased intron length resulting from TE proliferation.
• The identified ion channels provide insights into the evolution of autoresistance to toxins in poison frogs.