TNNT1

TNNT1
Identifiers
Aliases	TNNT1, ANM, NEM5, STNT, TNT, TNTS, troponin T1, slow skeletal type
External IDs	OMIM: 191041; MGI: 1333868; HomoloGene: 20704; GeneCards: TNNT1; OMA:TNNT1 - orthologs
Gene location (Human) Chr. Chromosome 19 (human)[1] Band 19q13.42 Start 55,132,698 bp[1] End 55,149,206 bp[1]
Gene location (Mouse) Chr. Chromosome 7 (mouse)[2] Band 7 A1|7 2.6 cM Start 4,507,569 bp[2] End 4,519,381 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in glutes Skeletal muscle tissue of biceps brachii thoracic diaphragm triceps brachii muscle gastrocnemius muscle Skeletal muscle tissue of rectus abdominis muscle of thigh vastus lateralis muscle deltoid muscle tibialis anterior muscle Top expressed in soleus muscle plantaris muscle ankle thoracic diaphragm medial geniculate nucleus extraocular muscle intercostal muscle lateral geniculate nucleus internal carotid artery human fetus More reference expression data BioGPS More reference expression data
Gene ontology Molecular function troponin T binding tropomyosin binding protein binding calcium ion binding calcium-dependent ATPase activity Cellular component cytosol troponin complex Biological process regulation of muscle contraction skeletal muscle contraction slow-twitch skeletal muscle fiber contraction negative regulation of muscle contraction transition between fast and slow fiber muscle filament sliding muscle contraction sarcomere organization cardiac muscle contraction Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 7138 21955 Ensembl ENSG00000105048 ENSMUSG00000064179 UniProt P13805 Q3B759 O88346 RefSeq (mRNA) NM_001126132 NM_001126133 NM_001291774 NM_003283 NM_001277903 NM_001277904 NM_011618 NM_001360154 RefSeq (protein) NP_001119604 NP_001119605 NP_001278703 NP_003274 NP_001264832 NP_001264833 NP_035748 NP_001347083 Location (UCSC) Chr 19: 55.13 – 55.15 Mb Chr 7: 4.51 – 4.52 Mb PubMed search [3] [4]
Wikidata
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Slow skeletal muscle troponin T (sTnT) is a protein that in humans is encoded by the TNNT1 gene.^[5][6]

The TNNT1 gene is located at 19q13.4 in the human chromosomal genome, encoding the slow twitch skeletal muscle isoform of troponin T (ssTnT). ssTnT is an ~32-kDa protein consisting of 262 amino acids (including the first methionine) with an isoelectric point (pI) of 5.95. It is the tropomyosin binding and thin filament anchoring subunit of the troponin complex in the sarcomeres of slow twitch skeletal muscle fibers.^[7][8][9] TNNT1 gene is specifically expressed in slow skeletal muscle of vertebrates, with one exception that dry land toad (Bufo) cardiac muscle expresses ssTnT other than cardiac TnT.^[10]

Three homologous genes have evolved in vertebrates, encoding three muscle type specific isoforms of TnT.^[9] Each of the TnT isoform genes is linked to one of the three troponin I^[11] isoform genes encoding the inhibitory subunit of the troponin complex, in chromosomal DNA to form three gene pairs: The fast skeletal muscle TnI (fsTnI)-fsTnT, ssTnI-cardiac (cTnT) and cTnI-ssTnT gene pairs. Sequence and epitope conservation studies suggested that genes encoding the muscle type specific TnT and TnI isoforms may have evolved from duplications of a fsTnI-like-fsTnT-like gene pair.^[12] Evolutionary lineage of the three TnI-TnT gene pairs shows that cTnI-ssTnT is the newest^[12] and most closely linked.^[13]

Protein sequence alignment demonstrated that TNNT1 genes are highly conserved among vertebrate species (Fig. 2), especially in the middle and C-terminal regions, while the three muscle type isoforms are significantly diverged among vertebrate species.^[8][9]

In mammalian and avian species, TNNT1 gene has a total of 14 exons, among which exon 5 encoding an 11-amino acid in the N-terminal region is alternatively spliced, generating a high molecular weight and a low molecular weight slow TnT splice forms (Jin, Chen et al. 1998).^[14][15] Biochemical studies showed that TnT splice forms have detectable different molecular conformation in the middle and C-terminal regions, producing different binding affinities for TnI and tropomyosin.^[8][9] The alternative splice forms of ssTnT play a role in skeletal muscle adaptation in physiologic and pathological conditions.^[16] Alternative splicing at alternative acceptor sites of intron 5 generates a single amino acid difference in the N-terminal region of ssTnT,^[15] of which functional significance has not been established.

A nonsense mutation E180X in the exon 11 of TNNT1 gene causes Amish Nemaline Myopathy (ANM), which is a severe form of recessive nemaline myopathy originally found in the Old Order Amish population in Pennsylvania, USA.^[17][18] Truncation of the ssTnT polypeptide chain by the E180X mutation deletes the tropomyosin-binding site 2^[19] as well as the binding sites for TnI and troponin C (TnC) in the C-terminal region (Fig. 3). Consistent with the recessive phenotype, the truncated ssTnT is incapable of incorporation into the myofilaments and completely degraded in muscle cells.^[20]

Tnnt1 gene targeted mouse studies reproduced the myopathic phenotypes of ANM.^[21][22] ssTnT null mice showed significantly decreased type I slow fibers in diaphragm and soleus muscles with hypertrophy of type II fast fibers, increased fatigability, and active regeneration of slow fibers (Wei, Lu et al. 2014).^[21]

Recent case reports identified three more mutations in TNNT1 gene to cause nemaline myopathies outside the Amish population. A nonsense mutation S108X in exon 9 was identified in a Hispanic male patient with severe recessive nemaline myopathy phenotype.^[23] A Dutch patient with compound heterozygous TNNT1 gene mutations that cause exon 8 and exon 14 deletions also presents nemaline myopathy phenotypes.^[24] A rearrangement in TNNT1 gene (c.574_577 delins TAGTGCTGT) leading to aberrant splicing that causes C-terminal truncation of the protein (L203 truncation) was reported in 9 Palestinian patients from 7 unrelated families with recessively inherited nemaline Myopathy.^[25]

Illustrated in Fig. 3, the S108X mutation truncates ssTnT protein to cause a loss of functional structures equivalent to that of E180X. The exon 8 deletion destructs the middle region tropomyosin-binding site 1.^[19][26] The L203 truncation deletes the binding sites for TnI and TnC but preserves both tropomyosin-binding sites 1 and 2.^[19] It remains to be investigated whether this novel mutation is able to bind the actin-tropomyosin thin filament in vivo and how it causes recessive nemaline myopathy.

Alternative splicing of exon 5 produces high and low molecular weight splice forms of ssTnT. The low molecular ssTnT was significantly upregulated in type 1 (demyelination) but not type 2 (axon loss) Charcot-Marie-Tooth disease,^[16] suggesting that structural modification of TnT in the myofilaments may contribute to adaptation to abnormalities in neuronal activation.

TNNT1 has been shown to interact with PRKG1.^[27]

^{[28] [29] [30]}

The 2016 version of this article was updated by an external expert under a dual publication model. The corresponding academic peer reviewed article was published in Gene and can be cited as: Bin Wei; J-P Jin (13 January 2016). "TNNT1, TNNT2, and TNNT3: Isoform genes, regulation, and structure-function relationships". Gene. Gene Wiki Review Series. 582 (1): 1–13. doi:10.1016/J.GENE.2016.01.006. ISSN 0378-1119. PMC 5325693. PMID 26774798. Wikidata Q37666010.

• GeneReviews/NCBI/NIH/UW entry on Nemaline Myopathy