Cajal bodies (CBs) are nuclear non-membrane bound organelles where small nuclear ribonucleoprotein particles (snRNPs) undergo their final maturation and quality control before they are released to the nucleoplasm. However, the molecular mechanism how immature snRNPs are targeted and retained in CBs has yet to be described. Here, we microinjected and expressed various snRNA deletion mutants as well as chimeric 7SK, Alu or bacterial SRP non-coding RNAs and provide evidence that Sm and SMN binding sites are necessary and sufficient for CB localization of snRNAs. We further show that Sm proteins, and specifically their GR-rich domains, are important for accumulating snRNPs in CBs. Accordingly, core snRNPs containing the Sm proteins, but not naked snRNAs, restore the formation of CBs after their depletion. Finally, we show that immature but not fully assembled snRNPs are able to induce CB formation and that microinjection of an excess of U2 snRNP-specific proteins, which promotes U2 snRNP maturation, chases U2 snRNA from CBs. We propose that the accessibility of the Sm ring represents the molecular basis for the quality control of the final maturation of snRNPs and the sequestration of immature particles in CBs.

• MeSH
• Cell Nucleus genetics   MeSH
• Coiled Bodies genetics   metabolism   MeSH
• HeLa Cells MeSH
• Humans MeSH
• Ribonucleoprotein, U2 Small Nuclear genetics   MeSH
• Gene Expression Regulation genetics   MeSH
• RNA, Small Nuclear genetics   MeSH
• Spliceosomes genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ribonucleoprotein, U2 Small Nuclear MeSH
• RNA, Small Nuclear MeSH
• U2 small nuclear RNA MeSH Browser

Spliceosomal snRNPs are complex particles that proceed through a fascinating maturation pathway. Several steps of this pathway are closely linked to nuclear non-membrane structures called Cajal bodies. In this review, I summarize the last 20 y of research in this field. I primarily focus on snRNP biogenesis, specifically on the steps that involve Cajal bodies. I also evaluate the contribution of the Cajal body in snRNP quality control and discuss the role of snRNPs in Cajal body formation.

• MeSH
• Coiled Bodies metabolism   MeSH
• Transcription, Genetic MeSH
• Humans MeSH
• RNA Processing, Post-Transcriptional MeSH
• Ribonucleoproteins, Small Nuclear genetics   metabolism   MeSH
• Spliceosomes MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Ribonucleoproteins, Small Nuclear MeSH

A majority of human genes contain non-coding intervening sequences - introns that must be precisely excised from the pre-mRNA molecule. This event requires the coordinated action of five major small nuclear ribonucleoprotein particles (snRNPs) along with additional non-snRNP splicing proteins. Introns must be removed with nucleotidal precision, since even a single nucleotide mistake would result in a reading frame shift and production of a non-functional protein. Numerous human inherited diseases are caused by mutations that affect splicing, including mutations in proteins which are directly involved in splicing catalysis. One of the most common hereditary diseases associated with mutations in core splicing proteins is retinitis pigmentosa (RP). So far, mutations in more than 70 genes have been connected to RP. While the majority of mutated genes are expressed specifically in the retina, eight target genes encode for ubiquitous core snRNP proteins (Prpf3, Prpf4, Prpf6, Prpf8, Prpf31, and SNRNP200/Brr2) and splicing factors (RP9 and DHX38). Why mutations in spliceosomal proteins, which are essential in nearly every cell in the body, causes a disease that displays such a tissue-specific phenotype is currently a mystery. In this review, we recapitulate snRNP functions, summarize the missense mutations which are found in spliceosomal proteins as well as their impact on protein functions and discuss specific models which may explain why the retina is sensitive to these mutations.

• Keywords
• Retinitis pigmentosa, snRNP, splicing,
• MeSH
• Introns MeSH
• Rats MeSH
• Humans MeSH
• Mutation, Missense MeSH
• Mice MeSH
• RNA Precursors genetics   metabolism   MeSH
• Retinitis Pigmentosa genetics   MeSH
• Ribonucleoproteins, Small Nuclear genetics   metabolism   MeSH
• RNA Splicing MeSH
• RNA Splicing Factors genetics   metabolism   MeSH
• Spliceosomes genetics   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• RNA Precursors MeSH
• Ribonucleoproteins, Small Nuclear MeSH
• RNA Splicing Factors MeSH