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How do piRNAs help prevent transposons from being copied in germ cells?

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Diagram of a DNA polynucleotide chain showing linked deoxyribose sugars, phosphate groups, and nitrogenous bases (adenine, guanine, cytosine, thymine), with an inset comparing ribose and uracil in RNA. — Nucleic acid A portion of the polynucleotide chain of deoxyribonucleic acid (DNA), with an inset showing the corresponding pentose sugar and pyrimidine base in ribonucleic acid (RNA).

PIWI-interacting RNAs (piRNAs) are small noncoding RNA molecules, typically 26 to 31 nucleotides in length, that play a critical role in maintaining genomic stability within the germ cells (sperm and eggs) of animals.1

They function as a regulatory mechanism to suppress the activity of transposons—often referred to as "jumping genes"—which are capable of moving and inserting themselves into various regions of the genome. piRNAs prevent these transposons from being copied by specifically targeting them for silencing, effectively keeping the genes from being transcribed in germ cells. Most piRNA molecules possess sequences that are complementary to specific transposons, allowing them to recognize and bind to their targets to inhibit their expression.21