A single miRNA can regulate several (maybe even hundreds of) transcripts and a single transcript can have binding sites for (or can be regulated by) several miRNAs of the same or different sequence. Several bioinformatic portals are available to predict miRNA targets (eg-Targetscan, PicTar, miRanda, etc), but not all targets are biologically validated. And as mentioned in the above comment, miRNA targets are context (tissue, miRNA/mRNA expression profile) specific.

The folowing articles may contain a target list for certain miRNAs (in specific types of cells/tissues) - CLIP seq data have given us insights about mRNA targets that miRNAs bind to - http://www.ncbi.nlm.nih.gov/pubmed/1953615, http://www.ncbi.nlm.nih.gov/pubmed/23622248. SILAC based approaches and microarrays also provide an idea of the protein and mRNA content respectively of miRNA targets - http://www.ncbi.nlm.nih.gov/pubmed/18668037, http://www.ncbi.nlm.nih.gov/pubmed/18668040.

In my experience, there are about tens to hundreds of protein-coding genes regulated by a microRNA. there are several factors related with miRNA targets: tissue expression profiles of miRNAs (tissue-specific or housekeeping); miRNA expression level (high expression of miRNA usually has more robust effects on targets)

MiRNAs identify certain "seed sequences" in sections of genes, thus, any gene that has such sequence targets is potentially regulated by the respective MiRNA, however, this depends on differential expression profiles as mentioned by Y Zhang above.

Different microRNA recognized several targets (bioinformatic docet) but only one or a couple governing a cascade of events. The necessary thing is focus temporally and spatially the pathway or pathology.

It is also different in animal and plants. Usually, in animal miRNAs can regulate more target genes than plants. Also, it is worth mentioning that comparing the expression miRNA and mRNA profiles is risky if the sample is complex (contains different kind of cells). Also, miRNA and mRNA can show correlated expression profiles and still be a target, e.g. the miRNA is avoiding the expression of the mRNA in the tissue where the miRNA is expressed.

MicroRNAs are ubiquitously present. There are only about 2000 miRNAs defined in humans till date. For this small number to control around 30000 genes, the miRNAs have to work over time!! Hence, each miRNA have come up with a way of controlling multiple targets. I won't say 'controlling' the expression of genes, but 'fine tuning' would be the right word. If you are interested you can see this publication by Selbach et al., Nature, 2008 about the role of miRNAs in tuning the protein synthesis of machinery.

Cheers.

A single miRNA can regulate several (maybe even hundreds of) transcripts and a single transcript can have binding sites for (or can be regulated by) several miRNAs of the same or different sequence. Several bioinformatic portals are available to predict miRNA targets (eg-Targetscan, PicTar, miRanda, etc), but not all targets are biologically validated. And as mentioned in the above comment, miRNA targets are context (tissue, miRNA/mRNA expression profile) specific.

The folowing articles may contain a target list for certain miRNAs (in specific types of cells/tissues) - CLIP seq data have given us insights about mRNA targets that miRNAs bind to - http://www.ncbi.nlm.nih.gov/pubmed/1953615, http://www.ncbi.nlm.nih.gov/pubmed/23622248. SILAC based approaches and microarrays also provide an idea of the protein and mRNA content respectively of miRNA targets - http://www.ncbi.nlm.nih.gov/pubmed/18668037, http://www.ncbi.nlm.nih.gov/pubmed/18668040.

As everyone had already said, there are multiple targets of each miRNA, only a subset of which that have been experimentally confirmed. However, you can find the predicted targets of each currently known miRNA on miRBASE. Which lists all the targets for 3p / 5p / * forms of the miRNAs based purely on their target sequences. Although some of these may prove to not be active target regions, it may help to direct your investigation.

Hope this helps.

According to me "miRNA" can target multiple "genes" for the "fine tuning" of there expression. Seed sequence and other sequence complementarity, to be presise partial complementarity, plays a great role in it, but it can not be the only thing, there are certain factors beyond our understanding ,yet now, that are also crutial as there is always discripencies between the predicted targets and validated targets. I think surface accessible area of the target,Ago and miR for the reaction is to be considered for this purpose because 3D orientation in physiological condition somtime restrict the chance of reaction.

Many, most likely. We have found that inactivation of a singe miRNA using an antagomir, by in vivo transfection, led to altered levels (up or down) of expression of about 1100 mRNAs. This to me suggests an extensive regulatory network, likely involving several miRNAs. Inactivation of one constituent of this network therefore creates a regulatory disequilibrium leading to effects on numerous mRNAs. We also found this to have an effect on the fenotype.

Thanks to All for the excellent suggestions! My questions started when we need to make a decision to use knockdown strategies by antisense DNA(the ole fashion way) or microRNA. It becomes very obvious that most researchers are using less specific strategy of miRNA. Why?

As Debasish said partially the drawback of multi targeting function of microRNA is due to instability of RNA structure and changing in its 3D structure which add another level of complexity to the field .To make the miRNA strategy more specific (at least in detection level), antisense oligonucleotides has been integrated in microRNA field which make them more stable structurally and as a result more specific .

http://www.sciencedirect.com/science/article/pii/S1046202307002095

http://www.exiqon.com/lna-technology

Will there be feedback mechanism to compensate down regulation of its protein(s)? How long will this compensation last?