Intercellular Junctions

Intercellular Junctions and Cell Communication

Cells can also communicate with each other via direct contact, which we refer to to as intercellular junctions. However, there are some differences in the ways that plant and animal cells do this. Plasmodesmata are junctions between plant cells, whereas animal cell contacts include tight junctions, gap junctions, and desmosomes.

Plasmodesmata

In general, long stretches of the plasma membranes of neighboring plant cells cannot touch one another. This is because they are separated by the cell wall that surrounds each cell. How then, can a plant transfer water and other soil nutrients from its roots, through its stems, and to its leaves? Such transport uses the vascular tissues (xylem and phloem) primarily. There also exist structural modifications which we refer to as plasmodesmata (singular = plasmodesma), numerous channels that pass between cell walls of adjacent plant cells, connect their cytoplasm, and enable material transportation from cell to cell, and thus throughout the plant (see image below).

Tight Junctions

A tight junction is a watertight seal between two adjacent animal cells (see image below). Proteins (predominantly two proteins called claudins and occludins) hold the cells tightly against each other.

This tight adherence prevents materials from leaking between the cells; tight junctions are typically found in epithelial tissues that line internal organs and cavities, and comprise most of the skin. For example, the tight junctions of the epithelial cells lining your urinary bladder prevent urine from leaking out into the extracellular space.

Desmosomes

Also found only in animal cells are desmosomes, which act like spot welds between adjacent epithelial cells (see image below). Short proteins called cadherins in the plasma membrane connect to intermediate filaments to create desmosomes. In fact, the cadherins join two adjacent cells together and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles.

Gap Junctions

Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow for the transport of ions, nutrients, and other substances that enable cells to communicate (see image below). Structurally, however, gap junctions and plasmodesmata differ.

Gap junctions develop when a set of six proteins (called connexins) in the plasma membrane arrange themselves in an elongated donut-like configuration called a connexon. When the pores (“doughnut holes”) of connexons in adjacent animal cells align, a channel between the two cells forms. Gap junctions are particularly important in cardiac muscle. The electrical signal for the muscle to contract passes efficiently through gap junctions. This allows the heart muscle cells to contract in tandem.

Video Animation of the Inner Life of the Cell

The Inner Life of the Cell was produced by XVIVO for Harvard University. In 2006, Harvard University teamed up with XVIVO to develop an animation that would take their cellular biology students on a journey through the microscopic world of a cell.

The Inner Life of the Cell follows a white blood cell’s movement along the endothelium and its response to an external stimulus — a process known as leukocyte extravasation. We hope this animation gives you a glimpse at the busy activities that take place inside a cell. MoreThinking created the narrated version of the animation below.