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A recent study on the Tra2b gene in mice has revealed a potential reason why certain segments of the genome called Ultra-Conserved Elements (UCEs) have remained unchanged for over 80 million years across species like humans, mice, rats, chickens, and even fish.

What are Ultra-Conserved Elements (UCEs)?

• Definition:DNA sequences at least 200 base pairs long that have remained perfectly identical across diverse species for tens of millions of years.
• Number in Human Genome:Around 500 UCEs have been identified in the human genome.
• Location:Found in both coding regions (genes) and non-coding regulatory regions like enhancers and silencers.
• Species Overlap:Identical UCEs are shared by humans, mice, rats, chickens, and fish, reflecting their evolutionary conservation.

Key Findings from the Tra2b Gene Study

• Research Insight:A UCE embedded in the first intron of the Tra2b gene acts as a “poison exon” to regulate production of the Tra2β protein, which is involved in RNA splicing.
• Mechanism:
  • When Tra2β levels rise, the UCE is included as an extra exon in the mRNA.
  • This exon contains multiple stop codons, halting protein synthesis.
  • The mRNA is then degraded, preventing excess Tra2β protein.
• Experimental Result:
  • Deleting this UCE in mouse sperm-producing cells led to overproduction of Tra2β, causing cell death and infertility.
  • This implies that any mutation in the UCE that disrupts its function would lead to infertility and thus prevent its transmission, explaining its evolutionary stability.

Significance of UCEs

• Evolutionary Importance:Their intolerance to mutation suggests they are critical for basic survival and reproductive success.
• Functional Role:
  • Do not typically code for proteins.
  • Regulate gene expression, often during early development, fertility, and immune response.
  • Act as enhancers, silencers, or splice regulators (as in the case of poison exons).
• Medical Relevance:
  • Help understand gene regulation and disease mechanisms.
  • Their conservation across species makes them valuable for comparative genomics and biomedical research.
  • Mice are used as model organisms due to ~85% genetic similarity with humans.