Glycoprotein Methods and Protocols - P2

Histological Methods for Detection of Mucin 29

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From: Methods in Molecular Biology, Vol. 125: Glycoprotein Methods and Protocols: The Mucins

Edited by: A. Corfield © Humana Press Inc., Totowa, NJ

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Histologically Based Methods for Detection of Mucin

Michael D. Walsh and Jeremy R. Jass

1. Introduction

Morphologically based studies on mucins allow structural characterization to be

linked to specific sites of synthesis and secretion. The histochemical approach to the

study of mucin is therefore highly informative. There is a correspondingly large body

of literature documenting the tissue distribution of mucins as demonstrated by mucin

histochemistry, lectin histochemistry, and immunohistochemistry (and various com￾binations of these methods). Two principal issues need to be considered in order to

maximize the potential value of morphologically based methodologies: (1) nature and

limitations of the individual techniques, and (2) interpretation and reporting of mucin

staining.

1.1. Nature and Limitations of Mucin-Staining Methods

Mucin histochemistry, lectin, and immunohistochemistry bring their own advan￾tages and disadvantages to the identification and characterization of epithelial mucin.

Remember that mucin can be well visualized with hematoxylin; Ehrlich’s hematoxy￾lin stains acid mucins (e.g., of salivary glands and intestinal goblet cells) deep blue.

The appearance is sufficiently characteristic to allow a mucin-secreting adenocarci￾noma to be diagnosed without the use of specific mucin stains.

Methods of tissue fixation influence mucin-staining. Formalin fixation is adequate

for most techniques using light microscopy, but fails to preserve the surface mucous

gel layer found throughout the gastrointestinal (GI) tract. Alcohol-based fixatives such

as Carnoy’s are required to demonstrate this structure (1). The duration of fixation and

nature of fixative used play significant roles in determining optimal protocols for the

demonstration of glycoproteins including mucins. The exact mechanisms of fixation,

particularly aldehyde fixation, remain unclear, although it appears that formalin, e.g.,

blocks protein amido groups and forms methylene bridges between amino acids, which

disturb the natural tertiary structure of proteins, rendering epitopes less amenable to

antibody binding to varying degrees (2). Since the initial description by Shi et al.