MadSci Network: Cell Biology

Re: why do some cells have many nucleus?

Date: Thu Jul 13 14:14:59 2000
Posted By: Jennifer Logan, Director for Science, Genetic Science Learning Center, Department of Human Genetics, University of Utah
Area of science: Cell Biology
ID: 962704474.Cb

Dear Becky:

This is a great question!

A cell that has many nuclei is called a “syncytium” (pronounced “sin-SISH- ium”). If you’re talking about more than one syncytium, you would say “syncytia” (“sin-SISH-ia”).

Where do syncytia occur in nature? You might know that skeletal muscle cells, such as the ones we use when we walk, are syncytia. Also, slime molds (a type of fungus) are syncytia. Early in its development, the fruit fly embryo is one big syncytium containing more than a thousand nuclei! Human cancer cells can have many nuclei, too.

Why do some cells contain many nuclei? You might find clues by thinking about how a specific type of syncytial cell is made, how it functions, and how having many nuclei might help the cell do its job.

Let’s consider the skeletal muscle cell. Each skeletal muscle cell is made up of many precursor cells, called myoblasts, which have fused together to form one long, thin cell with many nuclei. (To see illustrations and more detailed descriptions of muscle cells, visit this page.)

That’s HOW a muscle cell syncytium is made. Now let’s think about WHY. Are the multiple nuclei in each muscle cell important to its function? Or are they just a byproduct of the fusion of so many precursor cells? Could a skeletal muscle cell get by with just one nucleus? I would argue that it couldn’t, that the muscle cell needs all of those nuclei. Here’s why:

Think about the structure and function of these cells – they are much larger than other cell types, and they must be able to contract and relax. The machines responsible for muscle cell contraction, called “myofibrils,” occupy most of the cell’s interior. Myofibrils consist of many types of proteins, each of which does a specific job.

What do we know about nuclei, and how might they contribute to the function of the muscle cell? First of all, since the cell is full of myofibrils, and since myofibrils are made up of a lot of different proteins, it’s likely that the cell always has a need for more proteins. We know that nuclei are essential to the protein-making process, since they contain DNA, the genetic information that carries the instructions for making each protein. Also, the first step in making proteins, which involves transferring the information encoded in DNA to a messenger molecule (a process called “transcription”), takes place in the nucleus. The messenger molecule, called mRNA, then travels to the cell’s cytoplasm, where the information it carries is "translated" to build the actual protein.

In a large muscle cell, it’s possible that a single nucleus might not be able to satisfy the cell’s huge protein-making requirements. I would argue that the cell needs many nuclei to produce all of the proteins it needs.

Cell fusion is one way that syncytia can form. Syncytia can also be made through another mechanism, one that involves mitosis (my-TOE-sis), or cell division. This is the process by which a cell divides into two daughter cells, each of which is exactly like the original cell. Using your knowledge of mitosis, can you come up with a way that a cell with only one nucleus might turn into a syncytium?

(For a hint, go to A Primer on Cell Replication/Division, by Randall Oelerich, and scroll down the the Eukaryotic Cell Replication/Mitosis section.)

If you’d like to see another detailed description of mitosis, visit The Biology Project website. This page has a beautiful QuickTime animation of mitosis.

Jennifer Logan

Director for Science Genetic Science Learning Center
Eccles Institute of Human Genetics
University of Utah

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