The Lungfish Transcriptome: A Glimpse into Molecular Evolution Events at the Transition from Water to Land

Area of Science:

• Evolutionary biology
• Comparative genomics
• Vertebrate paleontology

Background:

• Lungfish and coelacanths are the sole extant sarcopterygian fish lineages.
• Lungfish exhibit unique phylogenetic positions and morphological similarities to fossil ancestors.
• The exceptionally large lungfish genome hinders whole-genome sequencing efforts.

Purpose of the Study:

• To establish the phylogenetic relationship of lungfish to tetrapods.
• To investigate the evolutionary dynamics of lungfish genes and transposable elements.
• To create a valuable resource for comparative vertebrate evolution studies.

Main Methods:

• Generation and assembly of a high-coverage lungfish reference transcriptome.
• Analysis of protein-coding gene evolution rates.
• Assessment of transposable element activity and diversity.
• Examination of gene families related to the water-to-land transition.

Main Results:

• Lungfish are identified as the closest relatives to land-adapted vertebrates, surpassing coelacanths in phylogenetic proximity.
• Protein-coding genes in lungfish exhibit a notably slow evolutionary rate, consistent with a "living fossil" phenotype.
• Transposable elements are highly active and diverse, likely contributing to the large genome size.
• Specific gene family changes linked to the aquatic-to-terrestrial transition were documented.

Conclusions:

• Lungfish represent a critical lineage for understanding vertebrate evolution and the water-to-land transition.
• The generated lungfish transcriptome serves as an essential tool for future comparative genomic and evolutionary research.
• The interplay between slow protein-coding gene evolution and active transposable elements provides insights into lungfish genome expansion and evolutionary stasis.