Description: The nucleus is usually the most prominent organelle in a eukaryotic cell viewed with a light microscope. The nucleus may provide valuable information about the cell in which it occurs.

Shape, Structure and Position of Nucleus

Most cells only contain 1 nucleus, so the locations and distributions of nuclei identify the locations and distributions of cells in tissues and organs. A few cells (skeletal muscle cells and osteoclasts) normally contain multiple nuclei. Multinucleated cells may originate either from fusion of mononuclear cells or from incomplete division. Mature, mammalian red blood cells lack a nucleus altogether.

The nucleus is usually centrally located in a cell. Location of the nucleus at one end of a cell indicates an accumulation of organelles (secretory granules, mitochondria, etc.) at the other end of the cell.

The nucleus is usually spherical. Extreme cell shapes may constrict the nucleus in the same directions that the cell is constricted, giving a clear hint of cell shape. A few cells such as granulocytes in the blood have complex nuclear shapes which are not related to cell shape, but the nuclear morphology of these cells is one of the major ways of recognizing them.

The staining intensity of the nucleus usually reflects the state of activity of the cell. In general, cells with larger proportions of potentially transcriptionally active DNA will have larger and lighter staining nuclei, while cells with little or no potentially transcriptionally active DNA will have smaller and darker staining nuclei.

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