Because list of probes on the BeadChip contains some of MIR genes (i.e. MIR1-2, MIR1200, MIR1202, MIR1203 etc.) however, as I remember correctly - the mature microRNAs don't contain the polyA tails, so the oligodT primers don't catch them.
Are these probes related to the pre-microRNA transcripts and do they always have polyA tail?
Thank you for any answers and suggestions!
Best regards,
Agata