MESSENGERRNA does not imbed itself into DNA. They encode info for a specific protein.
Mrna’s are made in the nucleus and then exported to the cytoplasm where the translation machinery, the machinery that actually makes proteins, binds to these mRNA molecules and reads the code on the mRNA to make a specific protein. So in general, one gene, the DNA for one gene, can be transcribed into an mRNA molecule that will end up making one specific protein.
https://www.genome.gov/genetics-glossary/messenger-rna