Alternative titles; symbols
HGNC Approved Gene Symbol: THOC1
Cytogenetic location: 18p11.32 Genomic coordinates (GRCh38): 18:214,520-268,047 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 18p11.32 | ?Deafness, autosomal dominant 86 | 620280 | Autosomal dominant | 3 |
In yeast, the TREX (transcription/export) complex contains the THO transcription elongation complex, which functions in cotranscriptional recruitment of mRNA export proteins to the nascent transcript. The human TREX complex contains ALY (THOC4; 604171), UAP56 (DDX39B; 142560), and the human counterpart of the THO complex, which includes THOC1. The human TREX complex appears to be recruited to spliced mRNAs late in the splicing reaction rather than by direct cotranscriptional recruitment, as in yeast (Masuda et al., 2005).
Using a modified yeast 2-hybrid screen of a lymphocyte cDNA library with the N-terminal 300 amino acids of the retinoblastoma protein (RB1; 614041) as bait, Durfee et al. (1994) isolated a cDNA encoding p84, a 657-amino acid protein. Immunoblot analysis showed expression of an 84-kD protein. Confocal microscopy demonstrated a nuclear matrix localization, specifically as speckles in the RNA-processing centers. Northern blot analysis revealed expression of a 2.1-kb transcript. Immunoprecipitation analysis of mouse tissues and human cell lines indicated ubiquitous expression of p84 and RB1, suggesting a role in regulating a basic function. Durfee et al. (1994) concluded that RB1 association with p84 would be an efficient means of concentrating the RB1 protein to subnuclear regions where active forms of several target-associated proteins (transcription factors) would be located.
By SDS-PAGE analysis of a 90-kD protein from nuclear extracts that interacted in pull-down assays with UAP56, followed by database searching, Strasser et al. (2002) obtained a full-length cDNA encoding HPR1. The predicted protein contains 657 amino acids and is conserved from yeast to humans.
By database analysis, followed by PCR of human lung, kidney, and fetal brain cDNA libraries, Gasparri et al. (2004) cloned full-length THOC1, which they called p84N5, and a splice variant, which they called p84N5s. The deduced p84N5s protein lacks the C-terminal RB1-binding domain, as well as the nuclear localization signal and death domain, found in full-length p84N5. EST database analysis detected orthologs of p84N5s in mouse and rat. RT-PCR detected independent and variable expression of both variants in all normal and tumor cell lines examined. Immunohistochemical analysis detected p84N5 predominantly in nucleus, whereas p84N5s was cytoplasmic. Time-lapse microscopy revealed that fluorescence-tagged p84N5 shuttled between the nucleus and cytoplasm of transfected human osteosarcoma and embryonic kidney cell lines. Expression of p84N5 was reduced in quiescent cells and highest during the G1-S transition.
By immunohistochemical analysis of mouse embryos, Wang et al. (2006) found widespread nuclear expression of Thoc1.
By cross-section and immunostaining of postnatal day 0 mouse inner ear, Zhang et al. (2020) observed expression of Thoc1 in inner and outer hair cells, but not in the saccule, utricles, spiral ganglion cells, or stria vascularis. Thoc1 protein was highly enriched in the hair cell nucleus and slightly distributed in the cytosol. In zebrafish, whole-mount in situ hybridization showed enrichment of thoc1 in the developing neuromast.
By sequence analysis, Dennehey et al. (2004) mapped the THOC1 gene to chromosome 18p, between the USP14 (607274) and COLEC12 (607621) genes. They mapped the mouse Thoc1 gene to a syntenic region of mouse chromosome 18p.
Stumpf (2023) mapped the THOC1 gene to chromosome 18p11.32 based on an alignment of the THOC1 sequence (GenBank BC010381) with the genomic sequence (GRCh38).
Functional studies in yeast led Strasser et al. (2002) to conclude that the TREX complex is specifically recruited to the transcribing gene and travels with the polymerase during transcriptional elongation. They suggested that it physically links proteins that function in mRNA export or transcription.
Gasparri et al. (2004) found that human p84N5 induced apoptosis when overexpressed in osteosarcoma cells. Cytoplasmic localization of p84N5 correlated with caspase-3 (CASP3; 600636) activation and apoptosis.
Using reciprocal immunoprecipitation with HeLa cells, Li et al. (2005) confirmed that THOC1 formed a complex with UAP56 and THO2 (300395). THOC1 also interacted with serine-phosphorylated RNA pol II (POLR2A; 180660). Chromatin immunoprecipitation analysis showed that THOC1 associated with promoter-distal regions of actively transcribing target genes. Knockdown of THOC1 expression via small interfering RNA reduced the expression of adenovirus lacZ and a subset of endogenous genes. Knockdown of THOC1 increased the formation of DNA-RNA hybrids and reduced the density of RNA pol II along the lacZ gene. THOC1 depletion also reduced the growth rate of 293 cells, increased cell sensitivity to DNA damage and loss of topoisomerase (see 126420) activity, and resulted in defects in nucleotide excision repair.
Using immunoprecipitation and mass spectrometric analysis of HeLa cell nuclear extracts, Masuda et al. (2005) found that the human TREX complex contained THO2, FSAP79 (THOC5; 612733), HPR1, UAP56, TEX1 (606929), FSAP35 (THOC6; 615403), ALY, and FSAP24 (THOC7; 611965). Immunodepletion and gel-filtration analyses revealed that THO2, HPR1, FSAP79, FSAP35, and FSAP24 were tightly associated in the THO complex, whereas UAP56, ALY, and TEX1 were more loosely associated. Immunoprecipitation of any TREX component efficiently immunoprecipitated spliced mRNA and cDNA transcripts, but not unspliced pre-mRNAs. Immunodepletion of any component had no effect on spliceosome assembly, splicing, or RNA stability. The TREX complex assembled on every mRNA examined. Mutation analysis showed that the C terminus of ALY was required for binding of both UAP56 and the THO complex. The C terminus of UAP56 was sufficient for ALY binding. The N terminus of UAP56 interacted weakly with the THO complex and TEX1, suggesting that other regions of UAP56 are required for maximal binding. Masuda et al. (2005) concluded that recruitment of the human TREX complex is not directly coupled to transcription, as in yeast.
In a large 4-generation Chinese family with autosomal dominant deafness (DFNA86; 620280), Zhang et al. (2020) identified heterozygosity for an L183V (606930.0001) substitution in the THOC1 gene. The mutation segregated fully with disease in the family and was not found in Han Chinese controls or public variant databases.
Wang et al. (2006) found that deletion of Thoc1 in mice was embryonic lethal in the late blastocyst state, with compromised hatching, implantation, and subsequent development. In culture, Thoc1-null day-3.5 embryos lacked cells of the inner cell mass. Lethality was associated with reduced Oct4 (POU5F1; 164177) expression. Thoc1 +/- mice were born at the expected mendelian frequency and appeared overtly normal.
Wang et al. (2009) developed a line of mice homozygous for a hypomorphic Thoc1 allele (Thoc1 H/H mice). Thoc1 H/H mice were smaller than their wildtype littermates, but they appeared otherwise normal, and most lived a typical life span. However, Thoc1 H/H males were infertile, and Thoc1 H/H females showed significantly reduced fertility. Thoc1 H/H males had reduced total sperm counts and percentage of motile sperm, as well as loss of spermatocyte viability and abnormal endocrine signaling. Thoc1 was not required for synaptonemal complex formation or progression through meiotic prophase, but it was required for normal gene expression during postnatal testis development.
Using CRISPR/Cas9, Zhang et al. (2020) generated thoc1-null zebrafish and observed that the number of hair cell clusters and neuromasts was markedly reduced, and hair cell number was reduced in both the neuromast and in the whole embryo. The mutant zebrafish also showed a significantly lower probability of a C-startle response than controls, suggesting a hearing problem in the thoc1 mutants. Morpholino knockdown resulted in morphants with the same phenotype, and both human THOC1 and zebrafish thoc1 mRNA significantly rescued the hair cell defects in the thoc1 morphants. Confocal imaging analysis of residual hair cells revealed abnormal morphology, including distorted shape and smaller size. TUNEL analysis showed that thoc1 deficiency resulted in apoptosis of 45% of hair cells and supporting cells in neuromasts. The authors found that the p53 (TP53; 191170) pathway as well as several apoptosis-associated genes were significantly upregulated in thoc1 mutant zebrafish, and depletion or inhibition of p53 significantly restored the number of hair cells and hair cell clusters in thoc1 morphants and alleviated apoptosis within neuromasts.
In a large 4-generation Chinese family (family SH) segregating autosomal dominant deafness (DFNA86; 620280), Zhang et al. (2020) identified heterozygosity for a c.547C-G transversion (c.547C-G, NM_005131) in exon 7 of the THOC1 gene, resulting in a leu183-to-val (L183V) substitution at a highly conserved residue within the elongation factor domain. Sanger sequencing confirmed the mutation, which segregated fully with disease in 9 affected and 12 unaffected family members and was not found in 1,000 Han Chinese normal-hearing controls, or the 1000 Genomes Project, ExAC, or gnomAD databases. Hair cell defects observed in thoc1 morphant zebrafish could be rescued by wildtype THOC1 mRNA but not c.547C-G mutant mRNA.
Dennehey, B. K., Gutches, D. G., McConkey, E. H., Krauter, K. S. Inversion, duplication, and changes in gene context are associated with human chromosome 18 evolution. Genomics 83: 493-501, 2004. [PubMed: 14962675] [Full Text: https://doi.org/10.1016/j.ygeno.2003.08.017]
Durfee, T., Mancini, M. A., Jones, D., Elledge, S. J., Lee, W.-H. The amino-terminal region of the retinoblastoma gene product binds a novel nuclear matrix protein that co-localizes to centers for RNA processing. J. Cell Biol. 127: 609-622, 1994. [PubMed: 7525595] [Full Text: https://doi.org/10.1083/jcb.127.3.609]
Gasparri, F., Sola, F., Locatelli, G., Muzio, M. The death domain protein p84N5, but not the short isoform p84N5s, is cell cycle-regulated and shuttles between the nucleus and the cytoplasm. FEBS Lett. 574: 13-19, 2004. [PubMed: 15358532] [Full Text: https://doi.org/10.1016/j.febslet.2004.07.074]
Li, Y., Wang, X., Zhang, X., Goodrich, D. W. Human hHpr1/p84/Thoc1 regulates transcriptional elongation and physically links RNA polymerase II and RNA processing factors. Molec. Cell. Biol. 25: 4023-4033, 2005. [PubMed: 15870275] [Full Text: https://doi.org/10.1128/MCB.25.10.4023-4033.2005]
Masuda, S., Das, R., Cheng, H., Hurt, E., Dorman, N., Reed, R. Recruitment of the human TREX complex to mRNA during splicing. Genes Dev. 19: 1512-1517, 2005. [PubMed: 15998806] [Full Text: https://doi.org/10.1101/gad.1302205]
Strasser, K., Masuda, S., Mason, P., Pfannstiel, J., Oppizzi, M., Rodriguez-Navarro, S., Rondon, A. G., Aguilera, A., Struhl, K., Reed, R., Hurt, E. TREX is a conserved complex coupling transcription with messenger RNA export. Nature 417: 304-308, 2002. [PubMed: 11979277] [Full Text: https://doi.org/10.1038/nature746]
Stumpf, A. M. Personal Communication. Baltimore, Md. 03/13/2023.
Wang, X., Chang, Y., Li, Y., Zhang, X., Goodrich, D. W. Thoc1/Hpr1/p84 is essential for early embryonic development in the mouse. Molec. Cell. Biol. 26: 4362-4367, 2006. [PubMed: 16705185] [Full Text: https://doi.org/10.1128/MCB.02163-05]
Wang, X., Chinnam, M., Wang, J., Wang, Y., Zhang, X., Marcon, E., Moens, P., Goodrich, D. W. Thoc1 deficiency compromises gene expression necessary for normal testis development in the mouse. Molec. Cell. Biol. 29: 2794-2803, 2009. [PubMed: 19307311] [Full Text: https://doi.org/10.1128/MCB.01633-08]
Zhang, L., Gao, Y., Zhang, R., Sun, F., Cheng, C., Qian, F., Duan, X., Wei, G., Sun, C., Pang, X., Chen, P., Chai, R., Yang, T., Wu, H., Liu, D. THOC1 deficiency leads to late-onset nonsyndromic hearing loss through p53-mediated hair cell apoptosis. PLoS Genet. 16: e1008953, 2020. [PubMed: 32776944] [Full Text: https://doi.org/10.1371/journal.pgen.1008953]