Nuclear speckles are self-organizing non-membrane bound sub-compartments found in the interchromatin regions of the nucleoplasm. Splicing speckles are enriched in splicing factors as well as factors involved in chromatin organization and modification, transcriptional regulation, mRNA modification, and mRNA export. Thus, they seem to have a general role in regulating gene expression. Paraspeckles are closely associated with splicing speckles and are built around a seeding scaffold of long noncoding RNA (lncRNA), termed nuclear paraspeckle assembly transcript 1 (NEAT1). Paraspeckles influence gene expression through sequestration of specific proteins and RNA molecules. The formation of both splicing speckles and paraspeckles seem to at least in part be driven by phase separation, and they are both highly dynamic assemblies, constantly exchanging factors with the nucleoplasm and other nuclear substructures.
Nuclear speckles can be seen as irregular and mottled spots inside the nucleoplasm. In interphase, the nucleus contains 20-50 splicing speckles, each measuring up to a few micrometers in diameter. Each speckle is made up of a cluster of many small granules connected by fine fibrils. Paraspeckles vary in size and abundance for different cell types, and can also be induced by various types of cellular stress. They have an elongated shape, with a diameter of about 360 nm and a length of 1-2 micrometers, each made up of small spherical units.
Read more about the proteome of nuclear speckles as a substructure of the nucleoplasm.