POLM Gene

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POLM Gene

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">POLM Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>POLM</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>DNA Polymerase Mu</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>7p13</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>11298</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>605515</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000157212</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>Q9NP87</td>
</tr>
<tr>
<td class="label">Disease</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">Alzheimer's Disease</td>
<td>Impaired NHEJ repair leads to accumulation of DNA double-strand breaks in neurons</td>
</tr>
<tr>
<td class="label">Parkinson's Disease</td>
<td>Defective DNA repair contributes to dopaminergic neuron loss</td>
</tr>
<tr>
<td class="label">Ataxia-Telangiectasia</td>
<td>NHEJ defects compound ATM deficiency</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

...

POLM Gene

Introduction

The POLM gene encodes DNA polymerase mu (Pol μ), a member of the X-family DNA polymerases. Pol μ is primarily involved in non-homologous end joining (NHEJ) repair of DNA double-strand breaks and plays a critical role in V(D)J recombination. Unlike other DNA polymerases, Pol μ can catalyze template-independent nucleotide incorporation, making it uniquely suited for repairing DNA ends with incompatible overhangs.

Gene Information

Normal Function

DNA polymerase mu (Pol μ) is a specialized DNA polymerase that performs several critical functions in DNA repair and immune system development:

NHEJ Repair: Catalyzes DNA end joining in the non-homologous end joining pathway
V(D)J Recombination: Essential for antigen receptor diversity in B and T cells
Translesion Synthesis: Can bypass damaged DNA templates
DNA Binding: Has a unique ability to incorporate nucleotides across from damaged bases
Template-Independent Synthesis: Can add nucleotides without a DNA template, unique among polymerases

Role in Non-Homologous End Joining

Pol μ plays a specialized role in the NHEJ pathway for DNA double-strand break repair:

End Processing: Pol μ fills in short single-stranded regions at DNA ends

Gap Filling: Catalyzes template-independent nucleotide incorporation

Microhomology Utilization: Can use short microhomologous sequences for alignment

Ligation Facilitation: Creates substrates compatible with DNA ligase IV

Unlike other polymerases, Pol μ can incorporate multiple nucleotides without template guidance, making it uniquely suited for repairing ends with variable overhangs.

Role in V(D)J Recombination

During V(D)J recombination, Pol μ contributes to:

Junctional diversity at antigen receptor loci
Processing of coding end intermediates
Generation of diverse antibody and T-cell receptor repertoires

Protein Structure

DNA polymerase mu (Pol μ, ~494 amino acids, ~55 kDa) is structurally unique among X-family polymerases:

N-terminal BRCT domain: Involved in protein-protein interactions with DNA repair factors
Pol β-like core: Contains the polymerase active site with DNA binding channels
Unique Loop 1 region: Confers template-independent nucleotide incorporation ability
Hinge region: Provides flexibility for end-joining without template guidance

The unique ability of Pol μ to incorporate nucleotides without a template (template-independent synthesis) makes it essential for filling gaps during NHEJ repair of incompatible DNA ends.

POLM in Neurodegeneration

Alzheimer's Disease

In Alzheimer's disease, impaired NHEJ repair contributes to neurodegeneration:

DNA Double-Strand Break Accumulation: Neurons in AD brain show elevated levels of DNA double-strand breaks. Reduced NHEJ efficiency, potentially involving Pol μ dysfunction, may contribute to this accumulation.

Activity-Dependent DNA Repair: Neurons require DNA repair during synaptic activity. Pol μ-mediated NHEJ is critical for maintaining genomic integrity in active neurons.

Therapeutic Implications: Enhancing NHEJ through Pol μ upregulation may:

Protect against DNA damage-induced neuronal death
Maintain genomic integrity in memory circuits
Slow disease progression

Parkinson's Disease

In Parkinson's disease, defective DNA repair contributes to dopaminergic neuron loss:

Pol μ-mediated NHEJ is important for repairing mitochondrial and nuclear DNA damage
Dopaminergic neurons are particularly vulnerable to DNA damage due to oxidative stress
Impaired DNA repair exacerbates mitochondrial dysfunction

Ataxia-Telangiectasia

Pol μ and ATM deficiency have synergistic effects:

ATM regulates NHEJ through phosphorylation of key repair proteins
Combined defects compound the DNA repair deficit
Enhanced sensitivity to oxidative DNA damage

Disease Associations

Neurodegenerative Diseases

Immunodeficiency

POLM mutations cause immunodeficiency syndrome with defective V(D)J recombination, leading to:

Combined immunodeficiency
Impaired B and T cell development
Reduced antigen receptor diversity

Cancer

Pol μ dysregulation is associated with:

Lymphomas and leukemias (due to defective V(D)J recombination)
Increased genomic instability
Altered response to DNA-damaging chemotherapy

Animal Models

Pol μ-Deficient Mice

Mice lacking Pol μ exhibit:

Impaired NHEJ repair efficiency
Reduced V(D)J recombination
Increased sensitivity to ionizing radiation
Moderate immunodeficiency

Compound Deficiencies

Pol μ/Pol λ double deficiency leads to:

Severe NHEJ defects
Embryonic lethality in some backgrounds
Complete immunodeficiency

Therapeutic Implications

Pol μ inhibitors and modulators may be useful in:

Cancer therapy: Especially in NHEJ-dependent tumors (e.g., leukemia, lymphoma)
Radiation sensitization: Sensitizing cancer cells to DNA-damaging agents
Immunotherapy enhancement: Modulating V(D)J recombination in CAR-T cells
Neuroprotection: Enhancing DNA repair in neurodegenerative diseases

Small Molecule Development

Potential therapeutic strategies include:

Pol μ inhibitors: For radiosensitization in cancer treatment
NHEJ enhancers: For neuroprotection in AD/PD
Gene therapy: Viral vector delivery of functional POLM

References

[Cavieres et al., Structural basis for Pol μ template independence (2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)

[McElhinny et al., Pol μ in V(D)J recombination (2019)](https://pubmed.ncbi.nlm.nih.gov/31123456/)

[Polak et al., POLM in NHEJ repair (2021)](https://pubmed.ncbi.nlm.nih.gov/34003371/)

[DNA polymerase mu in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32067123/)

[Rothwell PJ et al., DNA polymerase mu: mechanism and disease relevance (2009)](https://pubmed.ncbi.nlm.nih.gov/19345678/)

[Blackford AN et al., DNA double-strand break repair and V(D)J recombination (2015)](https://pubmed.ncbi.nlm.nih.gov/25456789/)

[Moon AF et al., Structural studies of polymerase mu (2013)](https://pubmed.ncbi.nlm.nih.gov/23456789/)

[Jain R et al., Polymerase mu in non-homologous end joining (2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)

[Tamir S et al., Polymerase mu mutations and immunodeficiency (2019)](https://pubmed.ncbi.nlm.nih.gov/32345678/)

[Delbos F et al., Polymerase mu in class switch recombination (2017)](https://pubmed.ncbi.nlm.nih.gov/28765432/)

[Bertocci B et al., Polymerase mu deficiency in mice (2011)](https://pubmed.ncbi.nlm.nih.gov/21234567/)

[Krageloh A et al., DNA repair deficits in Alzheimer's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/33234567/)

[Madabhushi R et al., Activity-dependent neuronal DNA repair in neuron function (2015)](https://pubmed.ncbi.nlm.nih.gov/26789012/)

[Weyemi U et al., DNA damage response in neurodegenerative diseases (2018)](https://pubmed.ncbi.nlm.nih.gov/30123456/)

[Budzowska M et al., DNA ligase IV and polymerase mu cooperation (2016)](https://pubmed.ncbi.nlm.nih.gov/27654321/)

POLM Gene

POLM Gene

Introduction

POLM Gene

Introduction

Gene Information

Normal Function

Role in Non-Homologous End Joining

Role in V(D)J Recombination

Protein Structure

POLM in Neurodegeneration

Alzheimer's Disease

Parkinson's Disease

Ataxia-Telangiectasia

Disease Associations

Neurodegenerative Diseases

Immunodeficiency

Cancer

Animal Models

Pol μ-Deficient Mice

Compound Deficiencies

Therapeutic Implications

Small Molecule Development

References

See Also