Factors affecting the yield of microRNAs from laser microdissectates of formalin-fixed tissue sections

Sixth generation Exiqon® locked nucleic acid miRCURY™ LNA microarrays were used to profile in duplicate the expression of microRNAs in 250 or 400 ng of RNA isolated from a laser microdissectate of a formalin-fixed and paraffin-embedded human non-small cell lung cancer tumor. Laser microdissection was performed on a hematoxylin-eosin-stained, 8 um-thick section of formalin-fixed and paraffin-embedded tissue. The microdissectate was treated with proteinase K overnight at 55 ºC. Total RNA from the lysate was then extracted using FFPE RNA Isolation Kit from Norgen Biotek® (Thorold, Canada). RiboGreen assay was used to quantify RNA in the preparation. Two-hundred-fifty or 400 ng of RNA was used in duplicate for dual-channel microarray-based microRNA expression profiling. Sample RNA was labeled with the Cy3-like Hy3™ dye, mixed with a human universal reference RNA (product number AM6000, Ambion®, Austin, TX) labeled with the Cy5-like Hy5™ dye, and hybridized to the two-color miRCURY™ arrays.