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PIWI-interacting RNAs, or piRNAs, are the most abundant short non-coding RNAs. More than 20,000 genes have been found in humans that code for piRNAs while only 2000 genes have been found for miRNAs. piRNAs can act at the transcriptional and post-transcriptional levels and have a vital role in silencing transposable elements present in germ cells. They are also involved in epigenetic silencing and activation. Previously, they were thought to function only in germ cells but new evidence suggests...
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Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...
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piRNA Defense Against Endogenous Retroviruses.

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Koala retrovirus (KoRV-A) infection offers a unique model to study germline defense. PIWI-interacting RNAs (piRNAs) process unspliced viral transcripts, initiating an adaptive immune response against the retrovirus.

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Area of Science:

  • * Molecular Biology
  • * Genetics
  • * Immunology

Background:

  • * Retroviruses and transposable elements can cause catastrophic DNA damage and mutations.
  • * PIWI-interacting RNAs (piRNAs) are crucial for maintaining germline integrity by silencing transposons.
  • * The mechanisms by which piRNA machinery recognizes new foreign genetic invaders are not fully understood.

Purpose of the Study:

  • * To investigate how exogenous retroviruses become fixed in a host genome.
  • * To understand the generation of retrovirus-targeting piRNAs in infected germ cells.
  • * To explore the piRNA machinery's recognition of foreign genetic elements and its role in genome defense.

Main Methods:

  • * Analysis of unspliced and spliced KoRV-A transcripts in koala testes.
  • * Investigation of piRNA processing from viral transcripts.
  • * Study of piRNA-guided epigenetic modifications at proviral loci.

Main Results:

  • * Unspliced KoRV-A transcripts in koala testes are processed into sense-strand piRNAs.
  • * This processing is proposed as an initial innate defense mechanism.
  • * The study provides insights into the establishment of an adaptive KoRV-A-specific genome immune response.

Conclusions:

  • * The piRNA machinery's recognition of new foreign genetic invaders is under investigation.
  • * Distinguishing between spliced and unspliced transcripts is a key aspect of this recognition.
  • * A mature genome immune response involves both sense and antisense piRNAs and epigenetic modifications.