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Exercise 9. Localization of Alpha Tubulin in Trachea and Esophagus using Immunohistochemistry - by Rosemary Barra, Ph. D.


A. Introduction

The cytoskeleton is the scaffolding of the cell consisting of a dynamic network of protein filaments. The cytoskeleton serves to maintain cell shape and also plays important roles in cell motion, cell division and the transport of vesicles and organelles within cells. The three types of protein filaments that comprise the cytoskeleton are the microtubules, the intermediate filaments, and the actin filaments.

Microtubules are hollow cylinders made up of tubulin polymers. Tubulin is itself a dimer containing two globular protein subunits alpha and beta tubulin. Tubulin molecules stack together to form a protofilament, and thirteen parallel protofilaments form a single microtubule.

The microtubules are structural supports in the cytoplasm and serve as substrates along which motor proteins can move. They are capable of growing and shrinking and this dynamic feature is responsible for a variety of cellular movements. For example, microtubules are major components of the mitotic spindle, which is used by cells to segregate their chromosomes during cell division.

Microtubules are also the major component of cilia and flagella. These tail like projections are covered by the plasma membrane and extend outwards from the cell. Cilia and flagella are composed of a central core consisting of nine outer pairs of microtubules and an additional two microtubules in the center. The central core also contains dynein, which is a microtubule-associated protein. The dynein is responsible for the sliding of the microtubules past one another, which serves to bend the cilium or flagellum. The bending occurs in the form of a wave that begins at the base of the cilium or flagellum and proceeds to the tip.

In this laboratory, you will determine the sites in the trachea and esophagus that contain high concentrations of alpha tubulin. A review of the basic histology of these organs may help you to interpret your results.