Nucleus speckle

The nuclear speckles are small subnuclear membraneless organelles or structures, also called the splicing factor (SF) compartments that correspond to nuclear domains located in interchromatin regions of the nucleoplasm of mammalian cells. Protein found in speckles serves as a reservoir of factors that participate in transcription and pre-mRNA processing. Speckles appear, at the immunofluorescence-microscope level, as irregular, punctuate structures, which vary in size and shape. Usually 25-50 speckles are observed per interphase mammalian nucleus. At the electronic-microscope level, they are composed of heterogeneous mixture of electro-dense particles with diameters ranging from 20-25 nm and are called interchromatin granules clusters (IGCs). Speckles are dynamic structures. Both their protein and RNA-protein components can cycle continuously between speckles and other nuclear locations depending on the transcriptional state of the cell. Structures similar to nuclear speckles have been identified in the amphibian oocyte nucleus (called B snurposomes) and in Drosophila melanogaster embryos, but not in yeast.

Source:http://purl.uniprot.org/locations/186