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I am new to micro RNAs. I have been trying to find the answer to the question if microRNAs are transcribed from the same DNA strand as the messenger RNAs encoded by the encompassing gene?

From the scientific articles I have read so far, I infer that it is the same strand. If so, does the transcription of microRNA and mRNA occur simultaneously?

Finally, does the strand from which the microRNA is transcribed have any implications for its interaction with its mRNA target?

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  • $\begingroup$ What do you mean by "the same gene as mRNAs"? What scientific article makes you think that? Try searching for microRNA promoters, e.g. In Drosophila. $\endgroup$ – David Dec 5 '17 at 19:28
  • $\begingroup$ @David What I meant was if the miRNA is created from the complementary DNA strand from where the mRNA is created. $\endgroup$ – nashynash Dec 6 '17 at 1:25
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The following bear on the question of the relationship of the transcription of microRNAs to that of the pre-mRNAs of protein-coding genes:

  • Some microRNAs (termed ‘intergenic’) do not reside in a protein-coding gene (e.g. Drosophila mir-31a). Here the question does not arise.

mir-31a

mir-11 and mir998

  • For those microRNAs that reside in a parent gene, the direction of transcription is generally, although not exclusively, the same as that of the transcript (ca. 70%, according to this review).

  • The question arises whether the intronic microRNAs are generated from the spliced introns of transcripts of their parent genes. One of many papers which consider this is by Ramalingam et al. (2014). It appears that in some cases this may be so, but in other cases this appears to be ruled out by a disparity between the expression profiles of parent genes and microRNAs, and between different microRNAs encoded in the same intron.

  • The co-directionality or otherwise of transcription of ‘parent’ mRNA and microRNA has no implications for the interaction of microRNAs with their, often numerous, ‘target’ mRNAs. This is because (1) there is no genetic relationship between parent mRNA and target mRNAs — the parent mRNA, lacking the intron that gave rise to the microRNA, is not the target; (2) the hairpin loop of the microRNA precursor (imperfect though it may be) in effect represents both strands, from which may be generated either the 5ʹ portion, the 3ʹ portion, or both, depending on the microRNA. The miRBase site contains information on relative abundance of 5ʹ- or 3ʹ-fragments for individual microRNAs, and the microrna.org resource lists potential target mRNAs.

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  • $\begingroup$ Thank you, David. That is really what I was looking for. By the way, even if a miRNA is not from the same DNA strand, it can form the miRNA-mRNA complex right? $\endgroup$ – nashynash Dec 7 '17 at 0:43
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    $\begingroup$ I have added a line to your question to include this concern, and have addressed it in my answer, which I have modified somewhat to improve it. The Ramalingam paper may be of interest. $\endgroup$ – David Dec 7 '17 at 14:45
  • $\begingroup$ That is very helpful. Thank you very much once again. $\endgroup$ – nashynash Dec 7 '17 at 14:52

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