 <unk> are subnuclear structures that are enriched in pre @-@ messenger RNA splicing factors and are located in the interchromatin regions of the nucleoplasm of mammalian cells . At the fluorescence @-@ microscope level they appear as irregular , <unk> structures , which vary in size and shape , and when examined by electron microscopy they are seen as clusters of interchromatin granules . <unk> are dynamic structures , and both their protein and RNA @-@ protein components can cycle continuously between speckles and other nuclear locations , including active transcription sites . Studies on the composition , structure and behaviour of speckles have provided a model for understanding the functional compartmentalization of the nucleus and the organization of the gene @-@ expression machinery splicing <unk> and other splicing proteins necessary for pre @-@ mRNA processing . Because of a cell 's changing requirements , the composition and location of these bodies changes according to mRNA transcription and regulation via <unk> of specific proteins . The splicing speckles are also known as nuclear speckles ( nuclear <unk> ) , splicing factor compartments ( SF compartments ) , interchromatin <unk> clusters ( <unk> ) , B snurposomes . B snurposomes are found in the amphibian <unk> nuclei and in <unk> <unk> embryos . B snurposomes appear alone or attached to the Cajal bodies in the electron <unk> of the amphibian nuclei . <unk> function as storage sites for the splicing factors . 
