There are three states of the gene: +/+, +/-, and -/-. When the gene is expressed as SIM2 -/-, it is considered disrupted and many physical malformations are seen, particularly in the craniofacial area. Individuals with SIM2 -/- have either a full or partial secondary palate cleft and malformations in the tongue and pterygoid processes of the sphenoid bone. These malformations cause aerophagia, or the swallowing of air, and postnatal death. Severe aerophagia leads to accumulation of air in the gastrointestinal tract, causing the belly to be distended.
It is thought that the over-expression of the SIM2 gene brings about some of the phenotypic deformities that are characteristic of Down syndrome. The presence of SIM2 mRNA in many parts of the brain known to show deformities in individuals with Down syndrome, as well as in the palate, oral and tongue epithelia, mandibular and hyoid bones.
There are two known isoforms of SIM2 which play different roles in various tissues. The isoform SIM2 Short (SIM2s) has been shown to be specifically expressed in mammary gland tissue. SIM2s is a splice variant which lacks exon 11 of SIM2. It has been researched that SIM2s acts in mammary gland development and has tumor suppressive characteristics specifically in breast cancer. In a mouse specimen, when SIM2s was not expressed in mammary epithelial cells there were development defects leading to cancer-like characteristics in the cells. The defects were increased cell proliferation, cellular invasion of local stroma, loss of cellular polarity, and loss of E-cadherin cellular adhesion molecules. These observations suggest that SIM2s is essential for proper mammary gland development. Experiments reintroducing SIM2s in human breast cancer cells allowed for the tumor suppressive characteristics to be observed. Comparing normal human breast cells to human breast cancer cells with immunohistochemical staining showed that SIM2s was expressed more in the normal than the cancerous. Reintroducing SIM2s expression in breast cancer cells showed a decrease in growth, proliferation, and invasiveness. SIM2s represses the actions of the matrix metalloprotease-3 gene (MMP3) which include cell migration, cancer progression, and epithelial to mesenchymal transitions (EMT). SIM2s also represses the SLUG transcription factor which in turn suppresses EMT. EMT suppression allows for E-cadherin to remain and for the cell to not undergo pathological EMT associated with tumor formation. These actions show the tumor suppressive effects of SIM2s in mammary epithelium.
Scientists can purposefully "knockout" or cause the gene to be disrupted. To do this, they perform homologous recombination and eliminate the predicted start codon and the following 47 amino acids. Then the EcoRI restriction site is introduced into the chromosome.
Muenke M, Bone LJ, Mitchell HF, Hart I, Walton K, Hall-Johnson K, et al. (November 1995). "Physical mapping of the holoprosencephaly critical region in 21q22.3, exclusion of SIM2 as a candidate gene for holoprosencephaly, and mapping of SIM2 to a region of chromosome 21 important for Down syndrome". American Journal of Human Genetics. 57 (5): 1074–1079. PMC 1801356. PMID 7485157. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1801356
"Entrez Gene: SIM2 single-minded homolog 2 (Drosophila)". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=6493
Shamblott MJ, Bugg EM, Lawler AM, Gearhart JD (August 2002). "Craniofacial abnormalities resulting from targeted disruption of the murine Sim2 gene". Developmental Dynamics. 224 (4): 373–380. doi:10.1002/dvdy.10116. PMID 12203729. S2CID 22828235. /wiki/Doi_(identifier)
Shamblott MJ, Bugg EM, Lawler AM, Gearhart JD (August 2002). "Craniofacial abnormalities resulting from targeted disruption of the murine Sim2 gene". Developmental Dynamics. 224 (4): 373–380. doi:10.1002/dvdy.10116. PMID 12203729. S2CID 22828235. /wiki/Doi_(identifier)
"Entrez Gene: SIM2 single-minded homolog 2 (Drosophila)". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=6493
Probst MR, Fan CM, Tessier-Lavigne M, Hankinson O (February 1997). "Two murine homologs of the Drosophila single-minded protein that interact with the mouse aryl hydrocarbon receptor nuclear translocator protein". The Journal of Biological Chemistry. 272 (7): 4451–4457. doi:10.1074/jbc.272.7.4451. PMID 9020169. https://doi.org/10.1074%2Fjbc.272.7.4451
Ooe N, Saito K, Mikami N, Nakatuka I, Kaneko H (January 2004). "Identification of a novel basic helix-loop-helix-PAS factor, NXF, reveals a Sim2 competitive, positive regulatory role in dendritic-cytoskeleton modulator drebrin gene expression". Molecular and Cellular Biology. 24 (2): 608–616. doi:10.1128/MCB.24.2.608-616.2004. PMC 343817. PMID 14701734. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC343817
Woods SL, Whitelaw ML (March 2002). "Differential activities of murine single minded 1 (SIM1) and SIM2 on a hypoxic response element. Cross-talk between basic helix-loop-helix/per-Arnt-Sim homology transcription factors". The Journal of Biological Chemistry. 277 (12): 10236–10243. doi:10.1074/jbc.M110752200. PMID 11782478. https://doi.org/10.1074%2Fjbc.M110752200
Moffett P, Reece M, Pelletier J (September 1997). "The murine Sim-2 gene product inhibits transcription by active repression and functional interference". Molecular and Cellular Biology. 17 (9): 4933–4947. doi:10.1128/mcb.17.9.4933. PMC 232345. PMID 9271372. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC232345
Meng X, Shi J, Peng B, Zou X, Zhang C (April 2006). "Effect of mouse Sim2 gene on the cell cycle of PC12 cells". Cell Biology International. 30 (4): 349–353. doi:10.1016/j.cellbi.2005.11.012. PMID 16530433. S2CID 46238281. /wiki/Doi_(identifier)
Shamblott MJ, Bugg EM, Lawler AM, Gearhart JD (August 2002). "Craniofacial abnormalities resulting from targeted disruption of the murine Sim2 gene". Developmental Dynamics. 224 (4): 373–380. doi:10.1002/dvdy.10116. PMID 12203729. S2CID 22828235. /wiki/Doi_(identifier)
Shamblott MJ, Bugg EM, Lawler AM, Gearhart JD (August 2002). "Craniofacial abnormalities resulting from targeted disruption of the murine Sim2 gene". Developmental Dynamics. 224 (4): 373–380. doi:10.1002/dvdy.10116. PMID 12203729. S2CID 22828235. /wiki/Doi_(identifier)
Kwak HI, Gustafson T, Metz RP, Laffin B, Schedin P, Porter WW (February 2007). "Inhibition of breast cancer growth and invasion by single-minded 2s". Carcinogenesis. 28 (2): 259–266. doi:10.1093/carcin/bgl122. PMID 16840439. https://doi.org/10.1093%2Fcarcin%2Fbgl122
Metz RP, Kwak HI, Gustafson T, Laffin B, Porter WW (April 2006). "Differential transcriptional regulation by mouse single-minded 2s". The Journal of Biological Chemistry. 281 (16): 10839–10848. doi:10.1074/jbc.m508858200. PMID 16484282. https://doi.org/10.1074%2Fjbc.m508858200
Kwak HI, Gustafson T, Metz RP, Laffin B, Schedin P, Porter WW (February 2007). "Inhibition of breast cancer growth and invasion by single-minded 2s". Carcinogenesis. 28 (2): 259–266. doi:10.1093/carcin/bgl122. PMID 16840439. https://doi.org/10.1093%2Fcarcin%2Fbgl122
Wellberg E, Metz RP, Parker C, Porter WW (March 2010). "The bHLH/PAS transcription factor singleminded 2s promotes mammary gland lactogenic differentiation". Development. 137 (6): 945–952. doi:10.1242/dev.041657. PMC 2834457. PMID 20150276. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2834457
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Kwak HI, Gustafson T, Metz RP, Laffin B, Schedin P, Porter WW (February 2007). "Inhibition of breast cancer growth and invasion by single-minded 2s". Carcinogenesis. 28 (2): 259–266. doi:10.1093/carcin/bgl122. PMID 16840439. https://doi.org/10.1093%2Fcarcin%2Fbgl122
Kwak HI, Gustafson T, Metz RP, Laffin B, Schedin P, Porter WW (February 2007). "Inhibition of breast cancer growth and invasion by single-minded 2s". Carcinogenesis. 28 (2): 259–266. doi:10.1093/carcin/bgl122. PMID 16840439. https://doi.org/10.1093%2Fcarcin%2Fbgl122
Kwak HI, Gustafson T, Metz RP, Laffin B, Schedin P, Porter WW (February 2007). "Inhibition of breast cancer growth and invasion by single-minded 2s". Carcinogenesis. 28 (2): 259–266. doi:10.1093/carcin/bgl122. PMID 16840439. https://doi.org/10.1093%2Fcarcin%2Fbgl122
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Laffin B, Wellberg E, Kwak HI, Burghardt RC, Metz RP, Gustafson T, et al. (March 2008). "Loss of singleminded-2s in the mouse mammary gland induces an epithelial-mesenchymal transition associated with up-regulation of slug and matrix metalloprotease 2". Molecular and Cellular Biology. 28 (6): 1936–1946. doi:10.1128/mcb.01701-07. PMC 2268409. PMID 18160708. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2268409
Shamblott MJ, Bugg EM, Lawler AM, Gearhart JD (August 2002). "Craniofacial abnormalities resulting from targeted disruption of the murine Sim2 gene". Developmental Dynamics. 224 (4): 373–380. doi:10.1002/dvdy.10116. PMID 12203729. S2CID 22828235. /wiki/Doi_(identifier)