Why are tissues embedded in paraffin?

A tissue sample is first preserved by fixing it in formaldehyde, also known as formalin, to preserve the proteins and vital structures within the tissue. Next, it is embedded in a paraffin wax block; this makes it easier to cut slices of required sizes to mount on a microscopic slide for examination.

How is RNA extracted from paraffin embedded tissue?

RNA extraction from paraffin-embedded tissues is made up of four steps. The first one is the deparaffinization and hydration of the tissue sections. The second is the digestion with a proteolytic enzyme such as proteinase K in the presence of effective RNase inhibition to remove proteins from the samples.

How do you store paraffin embedded tissue?

You can store paraffin blocks at room temperature in a box for years. But before you start sectioning again put them into the fridge for a couple of hours. This makes sectioning easier. Paraffin section which are not mounted on glas slides could also stored in flat boxes at room teperature over years.

How is paraffin embedded tissue section prepared?

Embed the tissue in paraffin at 58 °C….Because paraffin is immiscible with water, tissue must be dehydrated before adding molten paraffin wax.

  1. Immerse the tissue in 70% ethanol three times for 30 minutes each at room temperature.
  2. Immerse the tissue in 90% ethanol two times for 30 minutes each at room temperature.

What is the purpose of trimming the wax embedded tissue block?

The purpose of trimming is to create an even, flat surface in the area of interest in the tissue so that the histologists to not have to face (cut with the microtome) into the paraffin block as deeply when trying to get the first good sections for a slide.

How do you fix paraffin tissue?

Fix tissues with 10% formalin or other fixatives for 24-48 hours at room temperature. Make sure you have enough fixative to cover tissues. Fixative volume should be 5-10 times of tissue volume.

Can you extract RNA from paraffin-embedded tissue?

There are many advantages of using formalin-fixed paraffin-embedded (FFPE) tissues to develop biomarkers. Proteins, DNA, and RNA can be extracted from FFPE tissues and used for more ancillary molecular tests compared to samples from fresh frozen (FF) tissues [2].

How is tissue prepared for RNA extraction?

Preparation for homogenization should be carried out on dry ice, under liquid nitrogen. Pulverizing the tissue into a powder while keeping the tissue completely frozen is key to isolating intact total RNA.

How long do paraffin embedded tissues last?

The formalin-fixed/paraffin-embedded (FFPE) blocks should always be safely stored in fridge (4 degree Celsius) for 2 to 3 months.

How long do tissue slides last?

Histopathology slides for at least 10 years. Paraffin blocks for at least 2 years.

Why do we embed tissue?

Embedding is important in preserving tissue morphology and giving the tissue support during sectioning. When generating paraffin-embedded tissue samples, the tissue must be fixed before embedding in paraffin. Fixation is achieved by perfusion or immersion immediately following dissection.