Figure 3.

Model for the formation and dynamics of nuclear speckles. Nuclear speckles (also known as the SC35 domain, as illustrated on the left) are enriched with most splicing factors, hyper-phosphorylated Pol II, various chromatin remodeling factors, and RNA export factors. Co-transcriptional RNPs could be attracted to one another if they are not temporally resolved during transcription, resulting in an elevation in local concentration of transcription and splicing factors. As a result, the associated DNA might be looped near the interchromatin space in the nucleus. Thus, the formation of nuclear speckles could influence genome organization in the nucleus because some post-transcriptional RNPs that contain slow introns could be attracted to nearby nuclear speckles. It is possible that a population of pre-mRNAs could be spliced within or at the periphery of nuclear speckles and spliced mRNAs are then released into the nucleoplasm for export. Upon completion of splicing, splicing factors can be recruited from nuclear speckles to initiate new rounds of spliceosome assembly and splicing on nascent RNA. The dynamics of nuclear speckles is thus likely to be dependent on the transcription status of the cell.