Final answer:
miRNAs, siRNAs, and piRNAs all play a role in gene expression regulation through RNA interference, preventing the synthesis of proteins by targeting mRNA molecules.
Step-by-step explanation:
The similarity among miRNAs, siRNAs, and piRNAs is that c) All regulate gene expression through RNA interference. These small noncoding RNA molecules are key components in RNA interference (RNAi), a natural mechanism where gene expression is regulated by preventing mRNA molecules from guiding the synthesis of proteins. The way this is achieved is through the base pairing of these small RNA molecules to complementary mRNA molecules, leading to the degradation or inhibition of the mRNA and thus preventing protein synthesis. This is a crucial process that allows cells to regulate gene activity and maintain cellular integrity, especially as a defense mechanism against viral infections.