Microdissection
= Microdissection
\b[Microdissection] is the isolation of small selected structures or regions from a specimen under <microscope> guidance. It links the spatial organization studied in <histology> with assays of a chosen <cell population>. Unlike a <microtome>, which prepares thin sections, microdissection selects a particular region or constituent from material being examined.
Selection can be performed with fine mechanical tools or with instrument-assisted methods. A concrete landmark is the 1996 primary demonstration of <laser capture microdissection> by <Michael R. Emmert-Buck> and colleagues. Their apparatus placed a transparent <ethylene-vinyl acetate> <thermoplastic> film on a tissue section and used a carbon-dioxide <laser> pulse to activate the film over chosen cells. Adhesion allowed those cells to be collected. The paper demonstrated subsequent DNA/RNA amplification and enzyme recovery.<Laser capture microdissection by Michael R. Emmert-Buck and others>[Abstract; Science 274, 998–1001 (8 November 1996), DOI 10.1126/science.274.5289.998]{ref} This describes that published apparatus; capture and cutting methods need not use the same laser or transfer mechanism.
<Target purity versus cell-state change in microdissection> explains why spatial selection matters. In an original simple assay model, suppose target and background cells contribute calibrated signals $a$ and $b$ per cell. For target-cell fraction $p$, the per-cell mean of an equally weighted sample is $y=pa+(1-p)b$. With stipulated $a=100$, $b=0$, changing purity from 10% to 50% changes the mean from 10 to 50 units without any change in the target cells' own signal. An apparent increase can reflect enrichment rather than altered <gene expression>.
Conversely, a selected region need not be chemically pure. The footprint can include neighbouring cells, and tissue preparation or transfer can affect recovery of <DNA>, <RNA> and <proteins>. Normalization per cell, per total extracted RNA and per tissue area therefore asks different quantitative questions.
A useful experiment records the specimen image before and after selection, the chosen boundaries, collection yield and relevant background controls. Microdissection improves the connection between location and molecular measurement; it does not by itself prove cell identity, eliminate all contamination or establish that a recovered molecular difference is intrinsic to one cell type.