The nucleus is the largest organelle in the human cell and measures approximately 6 micrometers in diameter. It is enclosed by the nuclear membrane and contains a semi-fluid liquid, known as the nucleosol. Transport between the cytosol and nucleosol is controlled by nuclear pores. Underlying the nuclear membrane is a network of intermediate filaments, termed the nuclear lamina, which provides mechanical support and contributes to nuclear organization. The nucleoplasm harbours most of the human genome and a large plethora of proteins involved in DNA-related cellular processes, some of which are organized in substructures such as nucleoli, nuclear bodies and nuclear speckles. Inside the nucleus, the long DNA molecules are carefully compacted and organized together histones and a plethora of other proteins, in a complex known as chromatin. The nucleus serves to protect the genome, but also to compartmentalize and allow careful regulation of processes such as DNA replication and transcription.
The nucleoplasm can be visualized by staining with the fluorescent stain 4',6-diamidino-2-phenylindole (DAPI), which binds strongly to AT-rich regions of DNA. Nucleoli usually display a much weaker staining with DAPI, because of the lower amount of DNA in these regions. In the Cell Atlas, staining of the whole nucleus or of the nucleus without nucleoli, are annotated as nucleoplasm. Nuclear stainings can vary from smooth to punctate.
Read more about the proteome of the nucleoplasm.