Nucleoli

Nucleoli (singular: nucleolus) are small, round structures found inside the nucleus of most cells. They are made up of proteins and a special type of genetic material called RNA. The main job of nucleoli is to produce and assemble components needed to build ribosomes. Ribosomes are essential structures that help cells make proteins. Healthy, actively growing cells often have visible nucleoli, as these cells need many proteins to function properly.

How do pathologists examine nucleoli?

Pathologists examine nucleoli by looking closely at cells under a microscope. Tissue samples are usually stained with special dyes, such as hematoxylin and eosin (H&E), to help visualize the nucleoli clearly. Under the microscope, nucleoli typically appear as small, round spots within the nucleus that stain dark blue or purple with hematoxylin. Pathologists look at the number, size, shape, and prominence of nucleoli to help understand how active or abnormal a cell might be.

How do nucleoli change in health and disease?

The appearance of nucleoli can provide important clues about the health and behavior of cells. Healthy cells typically have small, discrete nucleoli. However, cells that are very active, rapidly dividing, or responding to stress often develop larger and more noticeable nucleoli. Cancer cells frequently have larger, more numerous, and more prominent nucleoli because they grow and divide very quickly, requiring continuous protein production.

In many cancers, pathologists pay special attention to changes in nucleoli because these changes can indicate aggressive or rapidly growing tumours. Larger or unusually shaped nucleoli can suggest a higher-grade cancer, meaning the tumour might be more aggressive and require more intensive treatment.

Certain viral infections can also affect nucleoli. Viruses may alter the size or shape of nucleoli as they take control of the cell’s machinery to replicate themselves. Recognizing these viral changes helps pathologists identify infections and guide appropriate treatments.