SIX1 (sine oculis homeobox homolog 1) (mammalian)

2005-11-01   Heide L Ford , Aaron N Patrick , Marileila Varella-Garcia 

Depts. of Obstetrics, Gynecology, Biochemistry, Molecular Genetics, University of Colorado Health Sciences Center, Fitzsimons Campus, Mail stop 8309, P.O. Box 6511, Aurora, CO 80045, USA




Atlas Image
View of the SIX1 gene which is composed of 2 exons that are 833 and 543 bps respectively, and a single 2,052 bp intron. Start and stop codon positions are shown.


The gene is composed of 2 exons and one intron and can be found on chromosome 14 at location 60,182,506-60,185,933.


The transcript length is 1,376 base pairs and the start of the transcript is located in Contig AL049874.3.1.193047. The transcript can be detected in a variety of tissues during mouse development (see below for protein expression) and this has also been confirmed at the protein level (using reporter genes). The transcript is further detected throughout normal mouse mammary gland development with levels being the highest in the embryonic mammary gland and decreasing as the mammary gland differentiates in pregnancy and lactation. In the adult human, it is detected in skeletal muscle, pituitary gland, salivary gland, kidney, lung, and trachea.




Atlas Image
View of the Six1 protein (total length 284 amino acids) that contains an N-terminal 115 amino acid Six domain (SD), and a 60 amino acid six-type homeodomain (HD). The SD is important for the interaction of Six1 with cofactors and also contributes to DNA binding along with the homeodomain.


Six1 belongs to the Six family of homeoproteins. Amino acids: 284. Predicted Molecular Weight: 32210 Dalton. It exists as a phosphoprotein and is hyperphosphorylated in mitosis.


During mouse development, Six1 is expressed in otic vesicles, nasal placodes, branchial arches, Rathkes pouch, dorsal root ganglion, proximal cranial ganglia, somites, cranial mesenchyme, nephrogenic cords, and limb mesenchyme. Six1 expression in muscles is present throughout myogenesis and into adulthood.




Six1 is a transcription factor that is known to play a role in the proliferation and survival of precursor cells during normal development in numerous tissues including, amongst others, the kidney, inner ear, and muscle. It is also demonstrated to play a role in the proliferation of cancer cells and in cancer metastasis. It is known to activate several target genes, including cyclin A1, c-MYC, GDNF, and SLC12A2.



Germline mutations of SIX1 are observed in branchio-oto-renal sydrome, an autosomal dominant developmental disorder that is characterized by kidney and urinary tract malformations and hearing loss. The three SIX1 mutations identified to date all interfere with the ability of the Six1 protein to interact with its Eya1 cofactor, and two of the identified mutations additionally affect Six1-DNA binding.


The SIX1 gene is amplified in about 5% of breast cancers (infiltrating ductal carcinomas). Overexpression of Six1 has been found in breast cancer, in Wilmstumors, and in rhabdomyosarcoma.

Implicated in

Entity name
Six1 is implicated in a number of cancers including breast cancer, rhabdomyosarcomas, and Wilms tumors. It has also been implicated in branchio-oto-renal syndrome.
Six1 is overexpressed in approximately 50% of primary breast cancers and 90% of metastatic lesions. Its overexpression in breast cancer has been linked to increased proliferation of breast cancer cells. Six1 is also a critical mediator of metastasis in a mouse rhabdomyosarcoma model.
breast cancer, wilms tumor, rhabdomyosarcoma, branchio-oto-renal syndrome,
The SIX1 gene is amplified in human breast cancer
Atlas Image
Idiogram of chromosome 14 (A) showing location of the SIX1 gene at 14q23 (clone RP11-1042B17, labeled in SpectrumRed). Clone RPMI-324B11 (labeled in SpectrumGreen) mapped at 14q11.2 was used as control. Metaphase spread (B) and interphase nuclei (C) of the non-malignant, immortalized MCF10A cell line showing two normal copies of chromosome 14 with signals generated by the SIX1 and control FISH probes. Metaphase spread of the mammary carcinoma cell line, 21MT2 (D), showing a normal copy of chromosome 14 with SIX1 (red) and control probe (green), two derivative chromosomes carrying only the SIX1 or the SIX1 and control signals and a copy of the derivative 14 chromosome with SIX1 gene amplification. Interphase nuclei from 21MT2 cells with multiple copies of red and green signals, including a cluster of SIX1 signals representing gene amplification (E).
SIX1 is overexpressed in several tumor types, including breast cancer, rhabdomyosarcomas, and Wilms tumors. It has been implicated in both the proliferation and metastasis of tumor cells.


Pubmed IDLast YearTitleAuthors
159550622005Slc12a2 is a direct target of two closely related homeobox proteins, Six1 and Six4.Ando Z et al
152549122004Expression of zebrafish six1 during sensory organ development and myogenesis.Bessarab DA et al
158045692005Six1 is not involved in limb tendon development, but is expressed in limb connective tissue under Shh regulation.Bonnin MA et al
86175001996Cloning of the human SIX1 gene and its assignment to chromosome 14.Boucher CA et al
146736352004Genetic determination of nephrogenesis: the Pax/Eya/Six gene network.Brodbeck S et al
155256622004Six1 promotes a placodal fate within the lateral neurogenic ectoderm by functioning as both a transcriptional activator and repressor.Brugmann SA et al
151238402004The Six1 homeoprotein stimulates tumorigenesis by reactivation of cyclin A1.Coletta RD et al
146280322003Signal transduction: an eye on organ development.Epstein JA et al
97705331998Abrogation of the G2 cell cycle checkpoint associated with overexpression of HSIX1: a possible mechanism of breast carcinogenesis.Ford HL et al
108018452000Cell cycle-regulated phosphorylation of the human SIX1 homeodomain protein.Ford HL et al
125009052002Six and Eya expression during human somitogenesis and MyoD gene family activation.Fougerousse F et al
105126831999Genomic cloning and characterization of the human homeobox gene SIX6 reveals a cluster of SIX genes in chromosome 14 and associates SIX6 hemizygosity with bilateral anophthalmia and pituitary anomalies.Gallardo ME et al
156535582005New perspectives on eye development and the evolution of eyes and photoreceptors.Gehring WJ et al
157884602005Six1 and Six4 homeoproteins are required for Pax3 and Mrf expression during myogenesis in the mouse embryo.Grifone R et al
152264282004Six1 and Eya1 expression can reprogram adult muscle from the slow-twitch phenotype into the fast-twitch phenotype.Grifone R et al
106175721999Synergistic regulation of vertebrate muscle development by Dach2, Eya2, and Six1, homologs of genes required for Drosophila eye formation.Heanue TA et al
122155332002Molecular interaction and synergistic activation of a promoter by Six, Eya, and Dach proteins mediated through CREB binding protein.Ikeda K et al
108785742000Six family genes--structure and function as transcription factors and their roles in development.Kawakami K et al
105573091999cDNA microarrays detect activation of a myogenic transcription program by the PAX3-FKHR fusion oncogene.Khan J et al
126686362003Altered myogenesis in Six1-deficient mice.Laclef C et al
128348662003Thymus, kidney and craniofacial abnormalities in Six 1 deficient mice.Laclef C et al
120579212002Gene expression in Wilms' tumor mimics the earliest committed stage in the metanephric mesenchymal-epithelial transition.Li CM et al
146280422003Eya protein phosphatase activity regulates Six1-Dach-Eya transcriptional effects in mammalian organogenesis.Li X et al
77205771995Homeobox genes and connective tissue patterning.Oliver G et al
146953752004Six1 controls patterning of the mouse otic vesicle.Ozaki H et al
109607942000Xenopus Six1 gene is expressed in neurogenic cranial placodes and maintained in the differentiating lateral lines.Pandur PD et al
158052642005Gene amplification is a mechanism of Six1 overexpression in breast cancer.Reichenberger KJ et al
106175651999From insect eye to vertebrate muscle: redeployment of a regulatory network.Relaix F et al
151410912004SIX1 mutations cause branchio-oto-renal syndrome by disruption of EYA1-SIX1-DNA complexes.Ruf RG et al
98266811998Expression of myogenin during embryogenesis is controlled by Six/sine oculis homeoproteins through a conserved MEF3 binding site.Spitz F et al
127837822003Six1 is required for the early organogenesis of mammalian kidney.Xu PX et al
147047892004Expression profiling identifies the cytoskeletal organizer ezrin and the developmental homeoprotein Six-1 as key metastatic regulators.Yu Y et al
128741212003The role of Six1 in mammalian auditory system development.Zheng W et al
154964422004Eya1 and Six1 are essential for early steps of sensory neurogenesis in mammalian cranial placodes.Zou D et al

Other Information

Locus ID:

NCBI: 6495
MIM: 601205
HGNC: 10887
Ensembl: ENSG00000126778


dbSNP: 6495
ClinVar: 6495
TCGA: ENSG00000126778


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
Transcriptional misregulation in cancerKEGGko05202
Transcriptional misregulation in cancerKEGGhsa05202

Protein levels (Protein atlas)

Not detected


Pubmed IDYearTitleCitations
222867702012The miR-106b-25 cluster targets Smad7, activates TGF-β signaling, and induces EMT and tumor initiating cell characteristics downstream of Six1 in human breast cancer.126
151410912004SIX1 mutations cause branchio-oto-renal syndrome by disruption of EYA1-SIX1-DNA complexes.119
197268852009The Six1 homeoprotein induces human mammary carcinoma cells to undergo epithelial-mesenchymal transition and metastasis in mice through increasing TGF-beta signaling.104
151238402004The Six1 homeoprotein stimulates tumorigenesis by reactivation of cyclin A1.87
205489462010A genome-wide association study of optic disc parameters.85
256700822015Recurrent DGCR8, DROSHA, and SIX homeodomain mutations in favorable histology Wilms tumors.75
256700832015Mutations in the SIX1/2 pathway and the DROSHA/DGCR8 miRNA microprocessor complex underlie high-risk blastemal type Wilms tumors.74
214271292011Common genetic variants associated with open-angle glaucoma.67
197268832009Six1 expands the mouse mammary epithelial stem/progenitor cell pool and induces mammary tumors that undergo epithelial-mesenchymal transition.66
206036202010MicroRNA-185 suppresses tumor growth and progression by targeting the Six1 oncogene in human cancers.59


Heide L Ford ; Aaron N Patrick ; Marileila Varella-Garcia

SIX1 (sine oculis homeobox homolog 1) (mammalian)

Atlas Genet Cytogenet Oncol Haematol. 2005-11-01

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