Biomedical Engineering Reference
In-Depth Information
development and occurs during the formation of cancers and their metastases.
h e movement and rearrangement of cells during the inl ammatory process is
possible because of the properties of adhesion molecules. Many pathologies can be
explained by changes in adhesion molecule properties, such as acute renal failure,
which has been reported to be associated with disruption of intercellular adhesions
in the proximal tubules of the kidneys. Much of our knowledge concerning
embryological migration, cell migration, and pathological events has come from
immunohistochemical studies.
INTRODUCTION
Adhesion molecules not only form gap junctions holding cells together and to
the extracellular matrix, but they also have an important role in development,
regulation of cell behavior, cell signaling, pathologies and cancer formation
(Sampson
et al.
2007), all of which have been demonstrated or discovered with
immunohistochemical techniques. h e adhesion molecules include cadherins,
integrins, claudins and occludins, as well as species that are less commonly
studied. Claudins and occludins are special adhesion molecules involved in tight
junctional sealing, as can be clearly seen in Fig. 1. Cadherins are trans-membrane
molecules that connect the cell interior, especially the actin cytoskeleton, with
the extracellular environment. Cadherins are named for their original source of
discovery, for example, E-cadherin from epithelium, N-from neuronal tissue,
P-from placental, R-from retina, VE-from vascular tissue, OB- from osteoblasts,
M-from myotubule and T- or H-from heart, but tissues have been found to possess
many of the various cadherins at various stages of their development, as recently
demonstrated in the bony growth plate, which appears to contain essentially all of
the cadherins in some spatial level (Sampson
et al.
2007).
Integrins are trans-membrane cell adhesion molecules that link the extracellular
matrix proteins, collagen, laminin and i bronectin, with the cytoskeleton. h ey are
composed of two trans-membrane subunits called α and β. h ere are specialized
attachments between integrins and actin i laments called focal contacts that allow
cells to pull on the substratum to which they are attached. Figure 2 is a micrograph of
focal attachments created by Total Internal Rel ection Fluorescence (TIRF) imaging
of a smooth muscle cell in culture using the antibody p-Tyr-FITC, Sigma #F3145
(clone #PT66). TIRF microscopy represents a method of exciting and visualizing
l uorophores present in the near-membrane region of live cells grown on glass
coverslips. TIRF microscopy is based on the total internal rel ection phenomenon
that occurs when light passes from a highly refractive medium (e.g., glass)
into one with lower refractive index (e.g., water, cell). Owing to the dif erence
between the refractive indices at the interface, only a short-range electromagnetic
disturbance called evanescent i eld will pass into the medium of lower refractive
index. h is type of excitation can be used to obtain high contrast l uorescence
images, with very low background and virtually no out-of-focus light
