Stathmin 1/oncoprotein 18, also known as STMN1, is a highly conserved 17 kDaprotein. Its function as an important regulatory protein of microtubule dynamics has been well characterized. Eukaryotic microtubules are one of three major components of the cell’s cytoskeleton. They are highly dynamic structures that continuously alternate between assembly and disassembly. Stathmin performs an important function in regulating rapid microtubule remodeling of the cytoskeleton in response to the cell’s needs. Microtubules are cylindrical polymers of α,β-tubulin. Their assembly is in part determined by the concentration of free tubulin in the cytoplasm.
At low concentrations of free tubulin, the growth rate at the microtubule ends is slowed and results in an increased rate of depolymerization (disassembly).
Stathmin interacts with two molecules of dimeric α,β-tubulin to form a tight ternary complex called the T2S complex. One mole of stathmin binds to two moles of tubulin dimers through the stathmin-like domain (SLD). When stathmin sequesters tubulin into the T2S complex, tubulin becomes non-polymerizable. Without tubulin polymerization, there is no microtubule assembly. Stathmin also promotes microtubule disassembly by acting directly on the microtubule ends. 
The rate of microtubule assembly is an important aspect of cell growth therefore associating regulation of stathmin with cell cycle progress. Regulation of stathmin is cell cycle dependent and controlled by the cell’s protein kinases in response to specific cell signals.Phosphorylation at four serine residues on stathmin named Ser16, Ser25, Ser38 and Ser63 causes weakened stathmin-tubulin binding. Stathmin phosphorylation increases the concentration of tubulin available in the cytoplasm for microtubule assembly. For cells to assemble the mitotic spindle necessary for initiation of the mitotic phase of the cell cycle, stathmin phosphorylation must occur. Without microtuble growth and assembly, the mitotic spindle cannot form, and the cell cycle is arrested. At cytokinesis, the last phase of the cell cycle, rapid dephosphorylation of stathmin occurs to block the cell from entering back into the cell cycle until it is ready.
Stathmin’s role in regulation of the cell cycle causes it to be an oncoprotein named oncoprotein 18 (op18). Stathmin (aka op18) can cause uncontrolled cell proliferation when mutated and not functioning properly. If stathmin is unable to bind to tubulin, it allows for constant microtubule assembly and therefore constant mitotic spindle assembly. With no regulation of the mitotic spindle, the cell cycle is capable of cycling uncontrollably resulting in the unregulated cell growth characteristic of cancer cells.
Mice without stathmin have deficiency in innate and learned fear. Stathmin−/− females do not assess threats well, leading to lack of innate parental care and adult social interactions. They lack motivation for retrieving pups and are unable to choose a safe location for nest-building. However, they have an enhancement in social interactions.
^ abcdJourdain L, Curmi P, Sobel A, Pantaloni D, Carlier MF (September 1997). "Stathmin: a tubulin-sequestering protein which forms a ternary T2S complex with two tubulin molecules". Biochemistry36 (36): 10817–21. doi:10.1021/bi971491b. PMID9312271.
^Clément MJ, Jourdain I, Lachkar S, Savarin P, Gigant B, Knossow M, Toma F, Sobel A, Curmi PA (November 2005). "N-terminal stathmin-like peptides bind tubulin and impede microtubule assembly". Biochemistry44 (44): 14616–25. doi:10.1021/bi0512492. PMID16262261.
^Atweh, George F.; Rubin, Camelia Iancu (August 2004). "The Role of Stathmin in the Regulation of the Cell Cycle". Journal of Cellular Biochemistry93 (2): 242–250. doi:10.1002/jcb.20187.
^Martel G, Nishi A, Shumyatsky GP (September 2008). "Stathmin reveals dissociable roles of the basolateral amygdala in parental and social behaviors". Proc. Natl. Acad. Sci. U.S.A.105 (38): 14620–5. doi:10.1073/pnas.0807507105. PMC2567152. PMID18794533.
Doye V, Le Gouvello S, Dobransky T et al. (1992). "Expression of transfected stathmin cDNA reveals novel phosphorylated forms associated with developmental and functional cell regulation". Biochem. J.287 (Pt 2): 549–54. PMC1133199. PMID1445213.
Labdon JE, Nieves E, Schubart UK (1992). "Analysis of phosphoprotein p19 by liquid chromatography/mass spectrometry. Identification of two proline-directed serine phosphorylation sites and a blocked amino terminus". J. Biol. Chem.267 (5): 3506–13. PMID1737801.
Melhem RF, Zhu XX, Hailat N et al. (1991). "Characterization of the gene for a proliferation-related phosphoprotein (oncoprotein 18) expressed in high amounts in acute leukemia". J. Biol. Chem.266 (27): 17747–53. PMID1917919.
Ferrari AC, Seuanez HN, Hanash SM, Atweh GF (1991). "A gene that encodes for a leukemia-associated phosphoprotein (p18) maps to chromosome bands 1p35-36.1". Genes Chromosomes Cancer2 (2): 125–9. doi:10.1002/gcc.2870020208. PMID2278968.
Maucuer A, Doye V, Sobel A (1990). "A single amino acid difference distinguishes the human and the rat sequences of stathmin, a ubiquitous intracellular phosphoprotein associated with cell regulations". FEBS Lett.264 (2): 275–8. doi:10.1016/0014-5793(90)80266-L. PMID2358074.
Zhu XX, Kozarsky K, Strahler JR et al. (1989). "Molecular cloning of a novel human leukemia-associated gene. Evidence of conservation in animal species". J. Biol. Chem.264 (24): 14556–60. PMID2760073.
Sobel A, Boutterin MC, Beretta L et al. (1989). "Intracellular substrates for extracellular signaling. Characterization of a ubiquitous, neuron-enriched phosphoprotein (stathmin)". J. Biol. Chem.264 (7): 3765–72. PMID2917975.
Maucuer A, Camonis JH, Sobel A (1995). "Stathmin interaction with a putative kinase and coiled-coil-forming protein domains". Proc. Natl. Acad. Sci. U.S.A.92 (8): 3100–4. doi:10.1073/pnas.92.8.3100. PMC42112. PMID7724523.
Curmi PA, Maucuer A, Asselin S et al. (1994). "Molecular characterization of human stathmin expressed in Escherichia coli: site-directed mutagenesis of two phosphorylatable serines (Ser-25 and Ser-63)". Biochem. J.300 (Pt 2): 331–8. PMC1138166. PMID8002936.
Kumar R, Haugen JD (1994). "Human and rat osteoblast-like cells express stathmin, a growth-regulatory protein". Biochem. Biophys. Res. Commun.201 (2): 861–5. doi:10.1006/bbrc.1994.1780. PMID8003023.
Marklund U, Brattsand G, Osterman O et al. (1994). "Multiple signal transduction pathways induce phosphorylation of serines 16, 25, and 38 of oncoprotein 18 in T lymphocytes". J. Biol. Chem.268 (34): 25671–80. PMID8245003.
Marklund U, Brattsand G, Shingler V, Gullberg M (1993). "Serine 25 of oncoprotein 18 is a major cytosolic target for the mitogen-activated protein kinase". J. Biol. Chem.268 (20): 15039–47. PMID8325880.
Beretta L, Dobránsky T, Sobel A (1993). "Multiple phosphorylation of stathmin. Identification of four sites phosphorylated in intact cells and in vitro by cyclic AMP-dependent protein kinase and p34cdc2". J. Biol. Chem.268 (27): 20076–84. PMID8376365.
Hosoya H, Ishikawa K, Dohi N, Marunouchi T (1997). "Transcriptional and post-transcriptional regulation of pr22 (Op18) with proliferation control". Cell Struct. Funct.21 (4): 237–43. doi:10.1247/csf.21.237. PMID8906359.
Larsson N, Marklund U, Gradin HM et al. (1997). "Control of microtubule dynamics by oncoprotein 18: dissection of the regulatory role of multisite phosphorylation during mitosis". Mol. Cell. Biol.17 (9): 5530–9. PMC232401. PMID9271428.