Geminin

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External IDs	GeneCards: [1]
Orthologs
Species	Human	Mouse
Entrez	n/a	n/a
Ensembl	n/a	n/a
UniProt	n/a	n/a
RefSeq (mRNA)	n/a	n/a
RefSeq (protein)	n/a	n/a
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Geminin, DNA replication inhibitor, also known as GMNN, is a protein in humans encoded by the GMNN gene.

Geminin is a nuclear protein that is present in most eukaryotics and highly conserved across species. Numerous functions have been elucidated for Geminin including roles in metazoan cell cycle, cellular proliferation, cell lineage commitment, and neural differentiation.

History

Geminin was originally identified as an inhibitor of DNA replication and substrate of the anaphase promoting complex (APC). Coincidentally, geminin was also shown to expand the neural plate in the developing Xenopus embryo.

Structure

Geminin is a nuclear protein made up of about 200 amino acids, with a molecular weight of approximately 25 kDa. It contains an atypical leucine-zipper coiled-coil domain. It has no known enzymatic activity nor DNA binding motifs.

Function

Cell cycle control

Geminin is absent during G₁ phase and accumulates through S, G₂ phase and M phases of the cell cycle. Geminin levels drop at the metaphase / anaphase transition of mitosis when it is degraded by the Anaphase Promoting Complex (APC/C).

S phase

During S phase, geminin is a negative regulator of DNA replication. In many cancer cell lines, inhibition of geminin by RNAi results in re-replication of portions of the genome, which leads to aneuploidy. In these cell lines, geminin knockdown leads to markedly slowed growth and apoptosis within several days. However, the same is not true for primary and immortalized human cell lines, where other mechanisms exists to prevent DNA re-replication. Since geminin knockdown leads to cell death in many cancer cell lines but not primary cell lines, it has been proposed as a potential therapeutic target for cancer treatment.

Mitosis

At the start of the S-phase until late mitosis, geminin inhibits the replication factor Cdt1, preventing the assembly of the pre-replicative complex. In early G1, the APC/C complex triggers its destruction through ubiquitination. Although inhibition of geminin by RNAi leads to impairment of DNA replication during the following cell cycle in many cancer cell lines, no such cell cycle defect is seen in primary and immortalized cell lines (although Cdt1 levels are still reduced in these cells).

Geminin therefore is an important player in ensuring that one and only one round of replication occurs during each cell cycle.

Developmental control

Geminin promotes early neural fate commitment by hyperacetylating the chromatin. This effect allows neural genes to be accessible for transcription, promoting the expression of these genes. Ultimately, geminin allows cells uncommitted to any particular lineage to acquire neural characteristics.

Geminin has also been shown to interact with the SWI/SNF chromatin remodeling complex. In neural precursor cells, high levels of geminin prevent terminal differentiation. When the interaction between geminin and SWI/SNF is eliminated, geminin's inhibition to this process is eliminated and neural precursors are allowed to differentiate.

Model organisms

Gmnn knockout mouse phenotype

Characteristic	Phenotype
Homozygote viability	Abnormal
Recessive lethal study	Abnormal
Fertility	Normal
Body weight	Normal
Anxiety	Normal
Neurological assessment	Normal
Grip strength	Normal
Hot plate	Normal
Dysmorphology	Normal
Indirect calorimetry	Normal
Glucose tolerance test	Normal
Auditory brainstem response	Normal
DEXA	Normal
Radiography	Normal
Body temperature	Normal
Eye morphology	Abnormal
Clinical chemistry	Normal
Plasma immunoglobulins	Normal
Haematology	Normal
Peripheral blood lymphocytes	Normal
Micronucleus test	Normal
Heart weight	Normal
Skin Histopathology	Normal
Brain histopathology	Normal
Salmonella infection	Normal
Citrobacter infection	Normal
All tests and analysis from

Model organisms have been used in the study of Geminin function. A conditional knockout mouse line, called Gmnn^{tm1a(KOMP)Wtsi} was generated as part of the International Knockout Mouse Consortium program, a high-throughput mutagenesis project to generate and distribute animal models of disease to interested scientists.

In addition, increased genomic instability and tumorigenesis have been observed in Geminin knockout mice in both the colon and lung.

Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion. Twenty six tests were carried out and three significant abnormalities were observed. A recessive lethal study found no homozygous mutant embryos during gestation, and therefore none survived until weaning. The remaining tests were carried out on heterozygous mutant adult mice and showed that females had abnormal lens morphology and cataracts.

Clinical significance

Geminin has been found to be overexpressed in several malignancies and cancer cell lines, while there is data demonstrating that Geminin acts as a tumor suppressor by safeguarding genome stability.

Further reading

• Maruyama K, Sugano S (1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID 8125298.
• Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A, Sugano S (1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID 9373149.
• McGarry TJ, Kirschner MW (1998). "Geminin, an inhibitor of DNA replication, is degraded during mitosis". Cell. 93 (6): 1043–53. doi:10.1016/S0092-8674(00)81209-X. PMID 9635433.
• Kroll KL, Salic AN, Evans LM, Kirschner MW (1998). "Geminin, a neuralizing molecule that demarcates the future neural plate at the onset of gastrulation". Development. 125 (16): 3247–58. PMID 9671596.
• Wohlschlegel JA, Dwyer BT, Dhar SK, Cvetic C, Walter JC, Dutta A (2000). "Inhibition of eukaryotic DNA replication by geminin binding to Cdt1". Science. 290 (5500): 2309–12. doi:10.1126/science.290.5500.2309. PMID 11125146.
• Bermejo R, Vilaboa N, Calés C (2002). "Regulation of CDC6, geminin, and CDT1 in human cells that undergo polyploidization". Mol. Biol. Cell. 13 (11): 3989–4000. doi:10.1091/mbc.E02-04-0217. PMC 133609. PMID 12429841.
• Biswas N, Sanchez V, Spector DH (2003). "Human cytomegalovirus infection leads to accumulation of geminin and inhibition of the licensing of cellular DNA replication". J. Virol. 77 (4): 2369–76. doi:10.1128/JVI.77.4.2369-2376.2003. PMC 141111. PMID 12551974.
• Kulartz M, Kreitz S, Hiller E, Damoc EC, Przybylski M, Knippers R (2003). "Expression and phosphorylation of the replication regulator protein geminin". Biochem. Biophys. Res. Commun. 305 (2): 412–20. doi:10.1016/S0006-291X(03)00773-3. PMID 12745091.
• Del Bene F, Tessmar-Raible K, Wittbrodt J (2004). "Direct interaction of geminin and Six3 in eye development". Nature. 427 (6976): 745–9. doi:10.1038/nature02292. PMID 14973488.
• Luo L, Yang X, Takihara Y, Knoetgen H, Kessel M (2004). "The cell-cycle regulator geminin inhibits Hox function through direct and polycomb-mediated interactions". Nature. 427 (6976): 749–53. doi:10.1038/nature02305. PMID 14973489.
• Sugimoto N, Tatsumi Y, Tsurumi T, Matsukage A, Kiyono T, Nishitani H, Fujita M (2004). "Cdt1 phosphorylation by cyclin A-dependent kinases negatively regulates its function without affecting geminin binding". J. Biol. Chem. 279 (19): 19691–7. doi:10.1074/jbc.M313175200. PMID 14993212.
• Melixetian M, Ballabeni A, Masiero L, Gasparini P, Zamponi R, Bartek J, Lukas J, Helin K (2004). "Loss of Geminin induces rereplication in the presence of functional p53". J. Cell Biol. 165 (4): 473–82. doi:10.1083/jcb.200403106. PMC 2172361. PMID 15159417.
• Ramachandran N, Hainsworth E, Bhullar B, Eisenstein S, Rosen B, Lau AY, Walter JC, LaBaer J (2004). "Self-assembling protein microarrays". Science. 305 (5680): 86–90. doi:10.1126/science.1097639. PMID 15232106.
• Ballabeni A, Melixetian M, Zamponi R, Masiero L, Marinoni F, Helin K (2004). "Human geminin promotes pre-RC formation and DNA replication by stabilizing CDT1 in mitosis". EMBO J. 23 (15): 3122–32. doi:10.1038/sj.emboj.7600314. PMC 514931. PMID 15257290.
• Saxena S, Yuan P, Dhar SK, Senga T, Takeda D, Robinson H, Kornbluth S, Swaminathan K, Dutta A (2004). "A dimerized coiled-coil domain and an adjoining part of geminin interact with two sites on Cdt1 for replication inhibition". Mol. Cell. 15 (2): 245–58. doi:10.1016/j.molcel.2004.06.045. PMID 15260975.
• Zhu W, Chen Y, Dutta A (2004). "Rereplication by depletion of geminin is seen regardless of p53 status and activates a G2/M checkpoint". Mol. Cell. Biol. 24 (16): 7140–50. doi:10.1128/MCB.24.16.7140-7150.2004. PMC 479725. PMID 15282313.
• Kulartz M, Knippers R (2004). "The replicative regulator protein geminin on chromatin in the HeLa cell cycle". J. Biol. Chem. 279 (40): 41686–94. doi:10.1074/jbc.M405798200. PMID 15284237.

External links

• GMNN+protein,+human at the US National Library of Medicine Medical Subject Headings (MeSH)