RNeasy FFPE Kit for RNA Extraction

The exact composition of Buffer RLT is confidential. This buffer is a proprietary component of RNeasy Kits. Buffer RLT contains a high concentration of guanidine isothiocycanate, which supports the binding of RNA to the silica membrane. Buffer RLT can be purchased separately (cat. no. 79216)

Note: note that ß-mercaptoethanol should be added to Buffer RLT before use to effectively inactivate RNAses in the lysate (10 µl ß-Mercaptoethanol per 1 ml Buffer RLT).

The integrity and size distribution of total RNA purified with RNeasy Kits can be checked by denaturing-agarose gel electrophoresis, the Agilent 2100 bioanalyzer, or the QIAxcel Advanced System with the QIAxcel RNA QC Kit v2.0.

The respective ribosomal species should appear as sharp bands on the stained gel. 28S ribosomal RNA bands should be present with an intensity approximately twice that of the 18S RNA band. If the ribosomal bands are not sharp, but appear as a smear of smaller sized RNAs, it is likely that the RNA sample has suffered major degradation during preparation.

Size of ribosomal RNAs from various sources

A maximum of 5 µl RNA eluate from RNeasy extraction procedures can be added to the reverse-transcription reaction with the QuantiTect Whole Transcriptome Kit.

Small amounts of RNA and DNA may be difficult to measure spectrophotometrically. Fluorometric measurements, or quantitative RT-PCR and PCR are more sensitive and accurate methods to quantify low amounts of RNA or DNA.

Fluorometric measurements are carried out using nucleic acid binding dyes, such as RiboGreen® RNA Quantitation Reagent for RNA, and PicoGreen® DNA Quantitation Reagent for DNA (Molecular Probes, Inc.).

Tissue-Tek O.C.T. is an embedding compound for cryosectioning, which is soluble in water. It mainly consists of glycols and synthetic resins. Tissue-Tek O.C.T. is used as matrix for cryosectioning of tissues. Using the O.C.T. the tissue samples can be positioned more easily in the microtome and have better qualities during sectioning.

Most cryosections are fixed using non-crosslinking agents. For isolation of RNA from tissue embedded in Tissue-Tek O.C.T. using non-crosslinking agents the RNeasy Plus Micro Kit or the RNeasy Micro Kit (Protocol: Total RNA Isolation from Microdissected Cryosections), or the RNeasy Mini Kit (RNeasy Mini Protocol for the isolation of Total RNA from Animal Tissue) give great results. We strongly recommend removing as much of the embedding compound as possible prior to RNA extraction from the sections. Please see QIAGEN News article, Issue 1 1998, 'Effects of malnutrition on expression of lactase in children' for successful RNA isolation from O.C.T.-embedded tissue using the RNeasy Mini Kit.

In case crosslinking agents (e.g. formaldehyde or glyoxal-containing) were used for fixation of the tissue for cryosectioning the RNeasy FFPE Kit is the perfect choice. The RNeasy FFPE Kit is especially designed for purifying total RNA from formalin-fixed tissue sections. Special lysis and incubation conditions reverse formaldehyde modification of RNA for improved results in downstream application. The crosslinking causes the RNA to break, resulting in overall smaller molecules, which look like a smear when analyzed on a formaldehyde gel.

In case DNA as well as RNA from precious samples is of interest from the identical sections, please have a look at the AllPrep DNA/RNA Kits for unfixed tissue or the AllPrep DNA/RNA FFPE Kit for fixed tissue.

The efficiency of downstream applications depends strongly on the purity of the RNA sample used.  Pure RNA should yield an A260/A230 ratio of around 2 or slightly above; however, there is no consensus on the acceptable lower limit of this ratio.  Possible candidates that can increase the A230 include “salt”, carbohydrates, peptides, and phenol (or aromatic compounds in general).  In our experience, the increased absorbance at 230 nm in RNA samples is almost always due to contamination with guanidine thiocyanate, present at very high concentrations in the lysis buffer or extraction reagent used in most RNA purification procedures.

Please find an article discussing the effect of low 260/230 ratios in RNA preparations on downstream applications on page 7 of QIAGEN Newsletter March 15, 2010 . In summary, we found that concentrations of guanidine thiocyanate of up to 100 mM in an RNA sample do not compromise the reliability of downstream applications.

To ensure efficient gDNA removal when doing an on-column digest using the RNase-Free DNase Set in combination with RNeasy Mini the following factors are crucial:

• prevent overloading by adjusting the amount of starting material to no more than the maximum amounts recommended in the RNeasy Mini Handbook
• ensure complete disruption and homogenization of the starting material as instructed in the section 'Disruption and homogenization of starting materials' of the handbook
• strictly follow the protocol for on-column DNase Digestion in Appendix D of the RNeasy Mini Handbook (you can let wash buffer RW1 incubate on the column for 3-5 minutes before centrifuging to enhance removal of excess gDNA prior to applying the enzyme)

In the rare case that trace amounts of genomic DNA are still detectable in sensitive downstream applications such as e.g., realtime RT-PCR, an in-solution digest using the RNase-Free DNAase set can be performed. Instructions are presented in Appendix C of the RNeasy MinElute Cleanup Handbook.

Alternatively, a second on-column digest can be carried out in future preparations, immediately following the RW1 wash after the first incubation with DNase.

The exact composition of Buffer RW1 is confidential. Buffer RW1 is a proprietary component of RNeasy Kits. Buffer RW1 contains a guanidine salt, as well as ethanol, and is used as a stringent washing buffer that efficiently removes biomolecules such as carbohydrates, proteins, fatty acids etc., that are non-specifically bound to the silica membrane. At the same time, RNA molecules larger than 200 bases remain bound to the column.

Note: Buffer RW1 should not be used for isolation of small RNAs, for example, microRNAs or fragmented RNA from formalin-fixed tissues, as these smaller fragments will be washed away.  Buffer RWT should be used instead.