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Jumping Genes (Transposons) and RNA Bridges

  • Context (TH): Research found that RNA bridges can be used to resurrect inactive jumping genes.

Jumping Genes (Transposons)

  • In 1948, Barbara McClintock, a scientist working on the genetics of maize plants, challenged the prevailing notion that genes were stable and arranged in an orderly manner on chromosomes.
  • She found that some genes could move within the genome and reversibly alter gene expression. These genes were called mobile elements/transposons/jumping genes.
  • This earned her the Nobel Prize in Physiology or Medicine in 1983.
  • Transposons are found in various life forms, including bacteriophages, bacteria, plants, worms, fruit flies, mosquitoes, mice, and humans.
  • More than 45% of the human genome consists of transposable elements. They are essential for genetic diversity but can lead to mutations and diseases.
  • However, most transposons have themselves inherited mutations and become inactive (cannot move within the genome).

Importance of Resurrection of Inactive Jumpings Genes (Transposons)

  • Transposons influence gene expression by turning it ‘on’ or ‘off’ using various epigenetic mechanisms.
  • They are called the tools of evolution for their ability to rearrange the genome and induce changes.
  • They may help treat chromosomal inversions or deletions, which current gene editing tools cannot do.
  • Researchers aim to revive inactive transposons for biomedical applications like genetic therapy.
  • The “sleeping beauty” transposon, which had become dormant in vertebrates millions of years ago, was reconstructed by studying fish genomes. This synthetic version was adapted for use in human cells.
  • Epigenetic mechanisms refer to modifications or changes in gene expression that do not involve alterations in the DNA sequence itself.

RNA Bridges or RNA-Guided Transposons: New Gene Editing Technique

  • A new RNA-guided gene editing system has been developed, inspired by a gene from a family of bacterial transposons (IS110 family). This gene instructs cells to produce an RNA molecule with two loops.
  • Transposons contain recombinase enzymes that bind to other DNA.
  • So, this RNA with two loops can bind to two pieces of DNA, forming a bridge between them, unlike the usual binding to just one piece. This RNA bridge is used to edit the DNA.
  • Each loop has a specific job.
    • Target binding loop: It recognises and binds to the target DNA that needs to be altered.
    • Donor binding loop: It recognises and binds to a separate piece of DNA used for the editing.
  • Researchers can programme each loop independently, mixing and matching target and donor DNA sequences as needed.
  • The RNA bridge had more than 60% insertion efficiency (the ability to introduce a desired gene) and 94% specificity (the ability to target the intended location on the genome).
  • This technique is also called the bridge recombinase mechanism.
  • IS110 family bacterial transposons are found abundantly in E. Coli bacteria.

RNA Bridges vs CRISPR-Cas9 Gene Editing Technique

Feature CRISPR-Cas9 RNA Bridge
Established Yes No (emerging)
Gene Editing method Cuts and relies on cellular repair Precise cutting and joining
Gene Editing capabilities Limited (small insertions/deletions of DNA sequences) More versatile (insertions, deletions, and inversions of DNA sequences)
Potential for Errors Higher (leaves small bits of nucleotides added/deleted during the repair process) Lower (makes a clean cut, making the edit specific and tidy)
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