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Related Experiment Videos

Epithelial cell polarity as reflected in enterocytes.

D Massey-Harroche1

  • 1Laboratoire de biologie et de biochimie de la nutrition, URA 1820, Faculté des Sciences de Saint Jérôme, Case 342, 13397, Marseille Cedex 20, France. dominique.massey-harroche@lbbn.u-3mrs.fr

Microscopy Research and Technique
|May 23, 2000
PubMed
Summary

This study explores how proteins reach their correct locations in intestinal cells. These cells are highly polarized, meaning their membrane is divided into apical and basolateral regions. The apical region includes a dense microvillar structure called the brush border. The study found that proteins in the basolateral region take a direct path from the trans-Golgi network to the membrane. Apical proteins, however, use two different pathways: one direct and one indirect, which involves a stop at the basolateral membrane. The researchers used specific markers like annexin XIII and the glycocalyx to track these pathways. They found that the indirect pathway is used by some apical proteins. The study highlights the complexity of protein sorting in these cells and its importance for maintaining epithelial function.

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Area of Science:

  • Cell biology of epithelial tissues
  • Membrane trafficking in polarized cells
  • Intestinal physiology and development

Background:

The organization of membrane domains in epithelial cells is a well-established concept. Prior research has shown that these cells divide their plasma membrane into apical and basolateral regions. The apical domain is especially notable in intestinal absorptive cells. These cells feature a dense microvillar structure known as the brush border. The brush border is not just a structural feature but a functional one. Some apical markers are concentrated in this domain, indicating a high degree of polarity. The glycocalyx and annexin XIII are examples of such markers. Their distinct localization suggests a complex sorting mechanism. This gap motivated further investigation into how proteins reach their correct membrane domains.

Purpose Of The Study:

This study aimed to clarify how apical and basolateral proteins reach their correct membrane domains in enterocytes. The researchers focused on the pathways used by apical markers. They wanted to determine whether these markers use a direct or indirect route. The basolateral pathway is already known to be direct. However, the apical pathway remains less clear. The study sought to compare the two possible apical routes. The motivation came from the need to understand how polarity is maintained. Efficient protein sorting is crucial for epithelial function. This work contributes to the broader understanding of cell polarity mechanisms.

Keywords:
Cell polarity mechanismsIntestinal epithelial cellsProtein sorting pathwaysMembrane trafficking in cells

Frequently Asked Questions

The study shows that apical proteins in enterocytes use two distinct pathways, direct and indirect, while basolateral proteins take a direct route.

The study used annexin XIII and the filamentous glycocalyx as apical markers to track their membrane localization.

The indirect pathway allows some apical proteins to transiently localize to the basolateral membrane before reaching their final apical destination.

The trans-Golgi network serves as the starting point for both basolateral and apical protein trafficking in enterocytes.

Related Experiment Videos

Main Methods:

The researchers used a combination of biochemical and imaging techniques. They examined the localization of apical and basolateral markers in mature enterocytes. The trans-Golgi network was a key focus for studying basolateral protein trafficking. For apical markers, they compared direct and indirect pathways. The indirect pathway involves a transient basolateral localization before reaching the apical membrane. The study used specific markers like annexin XIII and the glycocalyx. These markers were tracked using immunolabeling and electron microscopy. The researchers also analyzed the temporal sequence of marker distribution. This approach allowed them to distinguish between the two apical pathways.

Main Results:

The study found that basolateral markers follow a direct route from the trans-Golgi network to the basolateral membrane. In contrast, apical markers use two distinct pathways. One pathway is direct, while the other is indirect, involving the basolateral membrane. The indirect pathway is used by some apical proteins, such as annexin XIII. The glycocalyx remains anchored at the microvillar tips. Annexin XIII is concentrated in the lower three fourths of the microvilli. These findings suggest that different apical proteins use different sorting mechanisms. The study also showed that the brush border is a highly polarized domain. Protein sorting efficiency is essential for maintaining this polarity.

Conclusions:

The authors propose that mature enterocytes are hyperpolarized epithelial cells. The brush border is a specialized apical domain with a distinct composition. The study supports the idea that apical proteins use two distinct pathways. The direct and indirect routes depend on the specific protein involved. The basolateral pathway remains direct and well-defined. Efficient sorting is necessary for maintaining epithelial integrity. The findings highlight the complexity of membrane trafficking in polarized cells. The authors suggest that these mechanisms are critical for epithelial function.

The brush border is a dense microvillar structure with a restricted domain for apical markers like annexin XIII and the glycocalyx.

The authors propose that efficient protein sorting is essential for maintaining epithelial polarity and barrier integrity.