※ Nuclear speckle introduction

    Nuclear speckles or splicing speckles, also known as interchromatin granule clusters, are membrane-less nuclear organelles enriched in pre-mRNA splicing and transcription factors and play important roles in RNA metabolism, such as transcription, pre-mRNA splicing, 3′-end mRNA processing, and execution of mRNA nuclear export (1; 2). They are dynamic subnuclear structures, and their size, shape, and number can vary accompanied with RNA regulation, nuclear speckles disperse in high activity of mRNA processing when transcription or pre-mRNA splicing is inhibited, GSK-3β can regulate assembly of nuclear speckles (2). Because many naturally intronless mRNAs, including eight exogenously expressed and four endogenous ones, are proved to be associate with NSs, So Nuclear speckles (NSs) are thought to serve as splicing factor storage sites (3).

Reference
1. Lee, K. H., Zhang, P., Kim, H. J., Mitrea, D. M., Sarkar, M., Freibaum, B. D., et al. (2016) C9orf72 Dipeptide Repeats Impair the Assembly, Dynamics, and Function of Membrane-Less Organelles. Cell, 167(3), 774-788 e717. PMID: 27768896
2. Wang, K., Wang, L., Wang, J., Chen, S., Shi, M., & Cheng, H. (2018) Intronless mRNAs transit through nuclear speckles to gain export competence. J Cell Biol, 217(11), 3912-3929. PMID: 30194269
3. An, Y., Zou, Y., Cao, Y., Yao, M., Ma, N., Wu, Y., et al. (2019) The nuclear GSK-3beta regulated post-transcriptional processing of mRNA through phosphorylation of SC35. Mol Cell Biochem, 451(1-2), 55-67. PMID: 30030778