An overview of laser microdissection technologies

Graeme I. Murray
Acta histochemica 109 (2007) 171-176

In this review, Murray compared and contrasted two methods of laser microdissection, giving pros and cons for laser capture microdissection and laser cutting microdissection.  Both have the advantage over traditional microdissection techniques (requiring a scalpel or a fine stainless steel needle), because the older methods of microdissection are "slow, cumbersome, and require considerable dexterity."  In addition, using a scalpel or needle makes the tissue sample both hard to acquire and easy to contaminate.

Laser capture microdissection (as we do in our lab) requires a membrane attached to a cap, which is placed over the tissue section and melted with a laser.  The melted plastic attaches to the sample, cools within milliseconds, and allows the user to pick up only the small spot of the sample that they have chosen.  While this is convenient for collecting samples for use with assays that allow for amplification, like DNA and RNA, it is not very useful for protein assays, as the sample will be quite small.  The laser and the temperature changes do not seem to harm the sample, and the settings can be adjusted for use with tissues fixed in various ways.

Laser cutting microdissection was developed more recently and involves using a laser to "draw around" the desired cells, allowing them to detach from the slide.  The sample is then dropped or catapulted into a tube for collection.  This method does not require costly caps, heating and cooling of a membrane, or contact of any kind with the sample (thus cutting down on opportunities for contamination).  It allows for greater precision, as well, because laser capture microdissection has a larger laser diameter with a fixed shape (a circle) for sample collection, whereas laser cutting microdissection allows the user to outline their cells exactly (minimizing the collection of non-target cells that are adjacent to the target cell).  However, it works best when only a limited number of cells is needed, as laser capture microdissection allows for a more rapid collection of a large number of cells.

As to the matter of tissue preparation, Murray recommends that the tissue be exposed for as little time as possible to stains or rapid IHC techniques.  The biggest takeaway for tissue preparation is to avoid doing anything make the sample less ideal for the assays that one intends to do.  For us, because we wish to isolate the RNA, that means using fresh frozen tissue and avoiding letting the sections stay at room temperature for very long, so that the RNA has little opportunity to degrade.  Different types of molecular analysis will require different treatment of the tissue, though.