Transcribed Tc1-like transposons in salmonid fish

Area of Science:

• Genomics
• Evolutionary Biology
• Molecular Biology

Background:

• Mobile genetic elements (transposons) are abundant in vertebrate genomes but typically inactive.
• High-throughput sequencing reveals significant transcription of transposons in salmonid fish, despite translation inactivation.

Purpose of the Study:

• To investigate the structure and potential role of transcribed transposons in salmonid fish genomes.
• To compare transposon transcription levels in salmonids with other vertebrates.

Main Methods:

• Expressed Sequence Tag (EST) analysis to quantify transcribed transposons.
• Phylogenetic analysis of transposon reading frames.
• Cloning and sequencing of new DNA transposons.
• Microarray studies to assess transposon transcription under various stimuli.

Main Results:

• Salmonid fish exhibit 2.4-32 times higher transcribed transposon ratios than other vertebrates, with 68% belonging to the Tc1-family.
• Phylogenetic analysis suggests repeated, long-term transposition events into the fish genome.
• Newly identified DNA transposons show low divergence and high transcription in rainbow trout, with widespread presence in fish species.
• Transposon transcription is significantly upregulated by external stimuli like toxicity, stress, and bacterial antigens.
• Expression profiles of Tc1-like transposons correlate strongly with genes involved in defense response, signal transduction, and transcription regulation.

Conclusions:

• Salmonid genomes harbor abundant transcribed mobile genetic elements, notably Tc1-like transposons.
• Genome evolution and lateral transmission contribute to the diversity and persistence of these transposons in lower vertebrates.
• A subset of transposons remains transcribed, with enhanced expression during acute stress responses.