Nucleoli are dense, membrane-less structures found within the nucleus of eukaryotic cells. They are the sites where ribosomal RNA (rRNA) is synthesized and assembled with ribosomal proteins to form ribosomal subunits. The number, size, and shape of nucleoli can vary between cell types and different physiological states. Oval nucleoli refer to nucleoli with an elongated, oval-like shape.
The nucleolus is primarily composed of rRNA, ribosomal proteins, and various other proteins involved in rRNA synthesis, processing, and ribosome assembly. Its structure is organized into three main regions:
- Fibrillar center (FC): This is the central region of the nucleolus, where rRNA transcription occurs. It appears as a less electron-dense area under electron microscopy.
- Dense fibrillar component (DFC): Surrounding the fibrillar center, the DFC is where rRNA processing occurs. It has a higher electron density than the FC and is characterized by tightly packed fibrils.
- Granular component (GC): The outermost region of the nucleolus, the GC contains maturing ribosomal subunits. It appears as a granular structure under electron microscopy.
The shape of the nucleoli can be influenced by various factors, such as the cell type, the stage of the cell cycle, and the activity of rRNA transcription. Oval nucleoli may be observed in certain cell types or under specific conditions when the organization of the nucleolar components results in an elongated shape. Additionally, some cells may contain multiple nucleoli, which can vary in shape and size within the same nucleus.