MAPT — Microtubule Associated Protein Tau Gene Entity

MAPT — Microtubule Associated Protein Tau Gene Entity

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MAPT — Microtubule-Associated Protein Tau</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>MAPT</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Microtubule-Associated Protein Tau</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>17q21.31</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/4137" target="_blank">4137</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000193962" target="_blank">ENSG00000193962</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/157140" target="_blank">157140</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P10636" target="_blank">P10636</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td><a href="/diseases/alzheimers-disease">Alzheimer's Disease</a>, <a href="/diseases/progressive-supranuclear-palsy">PSP</a>, <a href="/diseases/corticobasal-degeneration">CBD</a>, <a href="/diseases/frontotemporal-dementia">FTD</a></td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Neurons (neurons), Axons, Hippocampus, Cortex</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Haplotypes & Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">H1/H2 haploty

MAPT — Microtubule Associated Protein Tau Gene Entity

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MAPT — Microtubule-Associated Protein Tau</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>MAPT</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Microtubule-Associated Protein Tau</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>17q21.31</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/4137" target="_blank">4137</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000193962" target="_blank">ENSG00000193962</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/157140" target="_blank">157140</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P10636" target="_blank">P10636</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td><a href="/diseases/alzheimers-disease">Alzheimer's Disease</a>, <a href="/diseases/progressive-supranuclear-palsy">PSP</a>, <a href="/diseases/corticobasal-degeneration">CBD</a>, <a href="/diseases/frontotemporal-dementia">FTD</a></td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Neurons (neurons), Axons, Hippocampus, Cortex</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Haplotypes & Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">H1/H2 haplotypes; P301L, P301S, R406W (FTDP-17)</td>
</tr>
</table>

MAPT — Microtubule-Associated Protein Tau Gene Entity

Overview

MAPT (Microtubule-Associated Protein Tau) is a gene located on chromosome 17q21.31 that encodes the [tau protein](/proteins/tau) — the central pathological player in [Alzheimer's disease](/diseases/alzheimers-disease) and related tauopathies. The discovery that tau forms the paired helical filaments and neurofibrillary tangles (NFTs) characteristic of AD revolutionized our understanding of neurodegeneration[@ballard2011]. MAPT is essential for axonal transport and neuronal viability, and mutations or dysregulation of MAPT lead to a spectrum of diseases collectively termed tauopathies.

The MAPT gene is notable for its complex genomic architecture, including a ~900 kb inversion that creates two distinct haplotypes (H1 and H2) in European populations. The H1 haplotype is associated with increased risk for [progressive supranuclear palsy](/diseases/progressive-supranuclear-palsy) (PSP), [corticobasal degeneration](/diseases/corticobasal-degeneration) (CBD), and [Alzheimer's disease](/diseases/alzheimers-disease)[@connor2009][@allen2012].

Gene Structure and Genomic Organization

Chromosomal Location and Haplotypes

The MAPT gene spans approximately 150 kb on chromosome 17q21.31. The H1 and H2 haplotypes arose from a single inversion event and are in strong linkage disequilibrium with specific variants. The H1 haplotype is the ancestral and more common form (~75% in Europeans) and is associated with increased risk for multiple tauopathies. The H2 haplotype appears to be protective against PSP[@connor2009].

Exon Structure and Splicing

The MAPT gene consists of 16 exons with complex alternative splicing. The central region (exons 2, 3, and 10) undergoes tissue-specific and developmentally regulated splicing, generating six major isoforms in the adult human brain[@andreadis2006][@goedert2006]:

| Isoform | N-terminal Inserts | Microtubule-Binding Repeats | Length |
|---------|-------------------|----------------------------|--------|
| 0N3R | None | 3 repeats | 352 aa |
| 0N4R | None | 4 repeats | 383 aa |
| 1N3R | One insert | 3 repeats | 379 aa |
| 1N4R | One insert | 4 repeats | 410 aa |
| 2N3R | Two inserts | 3 repeats | 395 aa |
| 2N4R | Two inserts | 4 repeats | 441 aa |

The balance between 3R and 4R tau isoforms is critical — imbalances contribute to pathology in several tauopathies. Exon 10 encoding the second microtubule-binding repeat is particularly relevant to disease pathogenesis.

Regulatory Elements

MAPT expression is modulated by multiple mechanisms:

• Epigenetic regulation: [DNA methylation](/entities/dna-methylation) at promoter regions
• Histone modifications: [HDAC](/entities/hdac-enzymes) activity influences transcription
• Non-coding RNAs: miR-132 family, miR-124, miR-9 regulate MAPT post-transcriptionally[@he2015]
• Transcription factors: SP1, REST, and others influence basal expression

Protein Structure and Isoforms

Tau Protein Architecture

The [tau protein](/proteins/tau) is produced in six isoforms (352-441 amino acids) with three functional domains[@mandelkow2010]:

N-terminal Projection Domain (residues 1-250): Projects away from microtubule surface, mediating interactions with neuronal membranes and kinases.

Proline-Rich Region (residues 151-243): Contains 85+ phosphorylation sites, mediates interactions with src-family kinases.

Microtubule-Binding Domain (residues 244-368): Contains 3-4 tandem repeat sequences (R1-R4) that bind to microtubules.

C-terminal Region (residues 369-441): Acidic tail regulating protein-protein interactions.

Conformational States

Tau exists in multiple states[@mandelkow2010]:

Normal Biological Function

Microtubule Stabilization

The primary function of tau is to bind and stabilize [microtubules](/entities/microtubules), essential for axonal transport and neuronal polarity[@baas2013]. Tau promotes microtubule polymerization by reducing the critical concentration of tubulin required for assembly and increasing the rate of microtubule nucleation. The N-terminal domain maintains proper spacing between microtubules in axons.

Axonal Transport

By stabilizing microtubules, tau indirectly supports axonal transport via motor proteins [kinesin](/proteins/kinesin-protein) and dynein. Hyperphosphorylation reduces tau-microtubule binding, releasing tau and impairing axonal transport — a well-documented early event in neurodegeneration[@stamer2002].

Synaptic Function

Tau localizes to synapses where it may regulate synaptic plasticity, mitochondrial trafficking, and neuronal signaling. Tau can be secreted in an activity-dependent manner, potentially serving as a propagation vector in tauopathies[@pooler2013].

Brain Region Expression

High expression in:

• Hippocampus (CA1 pyramidal neurons)
• Entorhinal cortex
• Cerebral cortex (layer V pyramidal neurons)
• Substantia nigra pars compacta
• Spinal cord motor neurons

Role in Neurodegenerative Diseases

Alzheimer's Disease

In AD, tau becomes abnormally hyperphosphorylated, aggregating into paired helical filaments (PHFs) and straight filaments that form [neurofibrillary tangles](/mechanisms/neurofibrillary-tangle-formation)[@braak1995]. NFT density correlates strongly with cognitive decline. Progression follows a predictable pattern: entorhinal cortex → hippocampus → limbic system → isocortex.

Key phosphorylation sites in AD[@gong2004]:

• Ser202/Thr205 (AT8 epitope)
• Ser396, Thr231, Ser422

Frontotemporal Dementia with Parkinsonism linked to Chromosome 17 (FTDP-17)

Over 50 pathogenic mutations in MAPT cause FTDP-17, inherited in autosomal dominant fashion. Mutations either alter exon 10 splicing (P301L, P301S, N279K) or reduce microtubule binding (K257T, G272V)[@hutton1998].

Progressive Supranuclear Palsy (PSP)

Strongly associated with the H1 haplotype of MAPT, particularly the H1c sub-haplotype. Characterized by 4R tau accumulation in globose NFTs and tufted astrocytes, affecting the basal ganglia, brainstem, and cerebellar nuclei[@williams2007].

Corticobasal Degeneration (CBD)

Another 4R tauopathy associated with MAPT H1 haplotype. Pathological tau forms astrocytic plaques and corticobasal balloons. Shares and distinct genetic risk factors with PSP[@ghetti2015].

Primary Age-Related Tauopathy (PART)

NFT pathology primarily in the medial temporal lobe without significant amyloid plaques. The relationship between MAPT haplotypes and PART is still being characterized[@crary2014].

Key Mutations and Variants

Pathogenic Mutations (FTDP-17)

| Mutation | Effect | Disease |
|----------|--------|---------|
| P301L | ↓ microtubule binding, ↑ aggregation | FTDP-17, CBD |
| P301S | ↓ microtubule binding, ↑ aggregation | FTDP-17 |
| K257T | ↓ microtubule binding | FTDP-17 |
| R406W | ↑ aggregation, altered binding | FTDP-17 |
| N279K | Alters splicing → 4R | FTDP-17 |
| S305S | Alters splicing → 4R | FTDP-17 |

Risk Haplotypes

• H1: Inverted, associated with PSP, CBD, and AD risk
• H2: Non-inverted, protective against PSP

Therapeutic Targets

Tau-Targeted Therapies[@delenclos2019]

Biomarkers[@schindler2020]

• CSF total tau (t-tau): Marker of neuronal damage
• CSF phosphorylated tau (p-tau181, p-tau217): AD-specific
• Plasma p-tau217 and p-tau181: Highly accurate for AD diagnosis
• Tau PET imaging (flortaucipir, MK-6240): In vivo visualization of pathology[@schll2017]

Mechanistic Pathway: MAPT in Tauopathies

Prion-Like Propagation

Tau pathology spreads through connected neural networks in a prion-like manner[@guo2011][@frost2009]:

Tau Oligomerization

Soluble tau oligomers are highly toxic — they disrupt synaptic function, impair mitochondrial function, activate inflammation, and serve as seeds for further aggregation.

Key Interactors in Tau Pathology

| Interactor | Role | Effect on Pathology |
|-----------|------|---------------------|
| [GSK3-beta](/entities/gsk3-beta) | Kinase | Major tau kinase, hyperphosphorylates multiple sites |
| [PP2A](/entities/pp2a) | Phosphatase | Accounts for ~70% of tau phosphatase activity |
| [CDK5](/proteins/cdk5-protein) | Kinase | Neuron-specific, phosphorylates Ser202/Thr205 |
| Fyn kinase | Tyrosine kinase | Mediates tau neurotoxicity |
| Pin1 | Prolyl isomerase | Regulates tau conformation |
| Hsp90 | Chaperone | Stabilizes mutant tau |

Epigenetic and Post-Translational Regulation

Phosphorylation[@gong2004]

Over 85 phosphorylation sites on tau. Balance between kinases (GSK3beta, CDK5, MARK, DYRK1A) and phosphatases (PP2A ~70% of activity) determines phosphorylation state. PP2A activity is reduced ~50% in AD brains.

O-GlcNAcylation[@liu2009]

Reduced in AD brains, can compete with phosphorylation — may protect against aggregation.

Acetylation[@min2010]

At K280, K369 promotes aggregation and reduces microtubule binding. SIRT1 deacetylase can remove these modifications.

See Also

• [MAPT Gene Page](/genes/mapt) — Comprehensive gene-level page
• [Tau Protein](/proteins/tau) — Protein-level page
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• [Corticobasal Degeneration](/diseases/corticobasal-degeneration)
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia)
• [GSK3-beta](/entities/gsk3-beta) — Major tau kinase
• [Neurofibrillary Tangle Formation](/mechanisms/neurofibrillary-tangle-formation)
• [Tau Propagation Mechanisms](/mechanisms/tau-propagation-mechanisms)

External Links

• NCBI Gene: [4137](https://www.ncbi.nlm.nih.gov/gene/4137)
• Ensembl: [ENSG00000193962](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000193962)
• OMIM: [157140](https://omim.org/entry/157140)
• UniProt: [P10636](https://www.uniprot.org/uniprot/P10636)
• Allen Human Brain Atlas: [MAPT expression](https://human.brain-map.org/microarray/search/show?search_term=MAPT)