--- ^{1Distinctive RNA splicing in ALS/FTD (2020)2020 · DOI 10.1038/s41593-020-00743-yOpen reference} title: SNRNP70 ^{2SNRNP70 mutations and disease (2019)2019 · DOI 10.1093/hmg/ddz125Open reference} --- ^{3Splicing factors in neurodegeneration (2021)2021 · DOI 10.1016/j.tins.2021.01.005Open reference}

SNRNP70

Overview

flowchart TD
    SNRNP70["SNRNP70"] -->|"associated with"| TREM2["TREM2"]
    SNRNP70["SNRNP70"] -->|"upregulates"| MHC_I["MHC-I"]
    SNRNP70["SNRNP70"] -->|"expressed in"| Alzheimer["Alzheimer"]
    SNRNP70["SNRNP70"] -->|"expressed in"| Als["Als"]
    SNRNP70["SNRNP70"] -->|"associated with"| Als["Als"]
    SNRNP70["SNRNP70"] -->|"associated with"| Alzheimer["Alzheimer"]
    SNRNP70["SNRNP70"] -->|"expressed in"| JUN["JUN"]
    SNRNP70["SNRNP70"] -->|"interacts with"| NTN3["NTN3"]
    SNRNP70["SNRNP70"] -->|"interacts with"| TARDBP["TARDBP"]
    SNRNP70["SNRNP70"] -->|"interacts with"| TAU["TAU"]
    SNRNP70["SNRNP70"] -->|"interacts with"| NTN1["NTN1"]
    SNRNP70["SNRNP70"] -->|"expressed in"| Endocytosis["Endocytosis"]
    SNRNP70["SNRNP70"] -->|"expressed in"| Complement["Complement"]
    SNRNP70["SNRNP70"] -->|"expressed in"| Exocytosis["Exocytosis"]
    style SNRNP70 fill:#4fc3f7,stroke:#333,color:#000

SNRNP70 (U1-70K, RNPU1L) is a core component of the U1 small nuclear ribonucleoprotein (snRNP) complex, which plays an essential role in pre-mRNA splicing. As part of the spliceosome, SNRNP70 recognizes the 5’ splice site and initiates the splicing cascade that removes introns from precursor messenger RNA. Dysregulation of SNRNP70 and other splicing factors has been strongly implicated in neurodegenerative diseases including ALS and FTD.

Introduction

SNRNP70 is one of the core proteins of the U1 snRNP, which is the first snRNP to recognize pre-mRNA splice sites. The protein is named for its molecular weight (70 kDa) and is also known as U1-70K due to its association with the U1 snRNA. SNRNP70 contains both RNA-binding domains and protein-protein interaction domains that enable it to function as a molecular hub in the splicing machinery.

Function

Pre-mRNA Splicing

SNRNP70 is essential for accurate pre-mRNA splicing:

1. 5’ Splice Site Recognition: SNRNP70 binds directly to the 5’ splice site consensus sequence (GU) through its RNA recognition motif (RRM) [1].

2. Spliceosome Assembly: SNRNP70 nucleates the assembly of the spliceosome complex, facilitating the formation of the E complex, A complex, and subsequent splicing intermediates.

3. Spliceosome Activation: The protein undergoes phosphorylation changes that regulate spliceosome activation and catalytic steps.

4. Alternative Splicing: SNRNP70 participates in regulated alternative splicing decisions that determine which exons are included in mature mRNAs.

Spliceosome Function

The U1 snRNP (with SNRNP70 as a key component) functions in the splicing cycle:

• Early Recognition: The U1 snRNP recognizes the 5’ splice site before the 3’ splice site is recognized.

• Cross-intron Recognition: SNRNP70 helps bridge the 5’ and 3’ splice sites together.

• Catalysis: The assembled spliceosome catalyzes two transesterification reactions to remove introns.

• Recycling: SNRNP70 is released and recycled for new splicing events.

Protein Domains

SNRNP70 contains several functional domains:

• RNA Recognition Motif (RRM): The central RRM binds to the 5’ splice site sequence.

• RS Domain: Arginine-serine rich region interacts with other splicing factors.

• N-terminal Glycine-Rich Region: Facilitates protein-protein interactions.

• Phosphorylation Sites: Multiple serine/threonine phosphorylation sites regulate function.

Interactions

SNRNP70 interacts with multiple splicing factors:

• U1 snRNP Proteins: SNRPA (U1-A), SNRNP70 (U1-C)

• U1 snRNA: Direct base-pairing with 5’ splice site

• SR Proteins: Serine/arginine-rich splicing factors

• hnRNP Proteins: Heterogeneous nuclear ribonucleoproteins

• Splicing Co-activators: Enhance or repress specific splicing events

Role in Neurodegenerative Diseases

Amyotrophic Lateral Sclerosis (ALS)

SNRNP70 and RNA splicing are prominently affected in ALS [2]:

• Splicing Dysregulation: Global alterations in RNA splicing patterns are observed in ALS motor neurons.

• TDP-43 Pathology: The aggregation of TDP-43 (TARDBP) disrupts snRNP assembly and function.

• U1 snRNP Loss: Loss of U1 snRNP components is observed in ALS spinal cord.

• Specific Splicing Changes: Aberrant inclusion/exclusion of specific exons contributes to disease.

Key Splicing Changes in ALS:

• Intron retention increases

• Exon skipping events accumulate

• Cryptic splice site usage increases

• Neuron-specific splicing programs are disrupted

Frontotemporal Dementia (FTD)

Similar splicing abnormalities are observed in FTD:

• TDP-43 Pathology: TDP-43 inclusions are a hallmark of both ALS and FTD.

• Splicing Regulation: SNRNP70-mediated splicing is dysregulated.

• Alternative Splicing: Specific splicing changes affect neuronal survival genes.

Spinal Muscular Atrophy (SMA)

While primarily caused by SMN1 deficiency:

• snRNP Assembly: Reduced SMN affects snRNP assembly, including U1 snRNP.

• Splicing Defects: Altered splicing patterns contribute to motor neuron dysfunction.

• Therapeutic Target: Modulating splicing is a key therapeutic strategy in SMA.

Retinitis Pigmentosa

SNRNP70 mutations cause inherited retinal degeneration:

• Photoreceptor Splicing: Disrupted splicing in photoreceptor cells.

• RNA Processing: Impaired RNA metabolism leads to photoreceptor death.

• Progressive Degeneration: Leads to progressive vision loss.

Alzheimer’s Disease

• Alternative Splicing Changes: Splicing dysregulation is observed in AD brains.

• Tau Splicing: Alternative splicing of tau exons is altered.

• APOE Splicing: Isoform expression is regulated by splicing factors.

Parkinson’s Disease

• SNP70 Expression: Altered expression in PD brains.

• RNA Processing: Global RNA processing abnormalities observed.

• α-Synuclein Splicing: Splicing factors may affect α-synuclein expression.

Therapeutic Implications

Targeting RNA splicing offers therapeutic opportunities:

1. Antisense Oligonucleotides: ASOs can correct aberrant splicing in disease.

2. Splicing Modulators: Small molecules that modulate spliceosome function.

3. Gene Therapy: Delivering splicing factors or correcting mutations.

4. Combination Approaches: Splicing therapy combined with other strategies.

See Also

• RNA Metabolism in Neurodegeneration

• Amyotrophic Lateral Sclerosis

• Frontotemporal Dementia

• Spinal Muscular Atrophy

• Retinitis Pigmentosa

• Alzheimer’s Disease

• Parkinson’s Disease

Background

The study of Snrnp70 Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

External Links

• PubMed - Biomedical literature

• Alzheimer’s Disease Neuroimaging Initiative - Research data

• Allen Brain Atlas - Brain gene expression data