ROCK inhibitor Y-27632 prevents porcine oocyte maturation

The inhibitor Y-27632 is a specific selective inhibitor of Rho-associated protein kinases (ROCKs), which are downstream effectors of Rho guanosine triphosphatease (GTPases) and regulate Rho-associated cellular functions, including actin cytoskeletal organization. Little is known regarding the effects of Y-27632 on mammalian oocyte maturation. In the present study, we investigated the effects of Y-27632 on porcine oocyte meiosis and possible regulatory mechanisms of ROCK during porcine oocyte maturation. We found that ROCK accumulated not only at spindles, but also at the cortex in porcine oocytes. Y-27632 treatment reduced ROCK expression, and inhibited porcine oocyte meiotic maturation, which might be because of the impairment of actin expression and actin-related spindle positioning. Y-27632 treatment also disrupted the formation of actin cap and cortical granule-free domain, which further confirmed a spindle positioning failure. Thus, Y-27632 has significant effects on the meiotic competence of mammalian oocytes by reducing ROCK expression, and the regulation is related to its effects on actin-mediated spindle positioning.     

The functional role of rho and rho-associated coiled-coil forming protein kinase in eotaxin signaling of eosinophils

The CC chemokine eotaxin plays a pivotal role in local accumulation of eosinophils. Very little is known about the eotaxin signaling in eosinophils except the activation of the mitogen-activated protein (MAP) kinase family. The p21 G protein Rho and its substrate Rho-associated coiled-coil forming protein kinase (ROCK) regulate the formation of stress fibers and focal adhesions. In the present study, we studied the functional relevance of Rho and ROCK in eosinophils using the ROCK inhibitor (Y-27632) and exoenzyme C3, a specific Rho inhibitor. Eotaxin stimulates activation of Rho A and ROCK II in eosinophils. Exoenzyme C3 almost completely inhibited the ROCK activity, indicating that ROCK is downstream of Rho. We then examined the role of Rho and ROCK in eosinophil chemotaxis. The eotaxin-induced eosinophil chemotaxis was significantly inhibited by exoenzyme C3 or Y-27632. Because extracellular signal-regulated kinase (ERK)1/2 and p38 MAP kinases are activated by eotaxin and are critical for eosinophil chemotaxis, we investigated whether Rho and ROCK are upstream of these MAP kinases. C3 partially inhibited eotaxin-induced phosphorylation of ERK1/2 but not p38. In contrast, neither ERK1/2 nor p38 phosphorylation was abrogated by Y-27632. Both C3 and Y-27632 reduced reactive oxygen species production from eosinophils. We conclude that both Rho and ROCK are important for eosinophil chemotaxis and reactive oxygen species production. There is a dichotomy of downstream signaling pathways of Rho, namely, Rho-ROCK and Rho-ERK pathways. Taken together, eosinophil chemotaxis is regulated by multiple signaling pathways that involve at least ROCK, ERK, and p38 MAP kinase.     

Rho kinases regulate corneal epithelial wound healing

We have previously shown that Rho small GTPase is required for modulating both cell migration and proliferation through cytoskeleton reorganization and focal adhesion formation in response to wounding. In the present study, we investigated the role of Rho kinases (ROCKs), major effectors of Rho GTPase, in mediating corneal epithelial wound healing. Both ROCK 1 and 2 were expressed and activated in THCE cells, an SV40-immortalized human corneal epithelial cell (HCEC) line, in response to wounding, lysophosphatidic acid, and heparin-binding EGF-like growth factor (HB-EGF) stimulations. The ROCK inhibitor Y-27632 efficiently antagonized ROCK activities without affecting Rho activation in wounded HCECs. Y-27632 promoted basal and HB-EGF-enhanced scratch wound healing and enhanced cell migration and adhesion to matrices, while retarded HB-EGF induced cell proliferation. E-cadherin- and beta-catenin-mediated cell-cell junction and actin cytoskeleton organization were disrupted by Y-27632. Y-27632 impaired the formation and maintenance of tight junction barriers indicated by decreased trans-epithelial resistance and disrupted occludin staining. We conclude that ROCK activities enhance cell proliferation, promote epithelial differentiation, but negatively modulate cell migration and cell adhesion and therefore play a role in regulating corneal epithelial wound healing.     

Y-27632, an Inhibitor of Rho-Associated Kinases, Prevents Tyrosine Phosphorylation of Focal Adhesion Kinase and Paxillin Induced by Bombesin: Dissociation from Tyrosine Phosphorylation of p130

A rapid increase in tyrosine phosphorylation of focal adhesion kinase (FAK), paxillin, and Crk-associated substrate (CAS) are prominent early events triggered by many G protein-coupled receptors (GPCRs), but the mechanisms involved remain unclear. Here, we examined whether the Rho-associated protein serine/threonine kinase family (ROCK) is a critical Rho effector in the pathway that links GPCR activation to the tyrosine phosphorylation of FAK, CAS, and paxillin. Treatment of Swiss 3T3 cells with Y-27632, a preferential inhibitor of ROCK, dramatically inhibited the formation of actin stress fibers, the assembly of focal contacts, and the increase in tyrosine phosphorylation of FAK and paxillin induced by bombesin in these cells. Surprisingly, we found that treatment with Y-27632 did not produce any detectable effect on bombesin-elicited CAS tyrosine phosphorylation even at the highest concentrations of Y-27632 tested. HA-1077, a preferential inhibitor of ROCK activity structurally unrelated to Y-27632, also attenuated the increase in the tyrosine phosphorylation of FAK and paxillin but did not affect the tyrosine phosphorylation of CAS induced by bombesin in Swiss 3T3 cells. The results demonstrate that ROCK-dependent tyrosine phosphorylation of FAK and paxillin can be dissociated from a ROCK-independent pathway leading to tyrosine phosphorylation of CAS.     

Y-27632, an inhibitor of Rho-associated kinases, prevents tyrosine phosphorylation of focal adhesion kinase and paxillin induced by bombesin: dissociation from tyrosine phosphorylation of p130(CAS)

A rapid increase in tyrosine phosphorylation of focal adhesion kinase (FAK), paxillin, and Crk-associated substrate (CAS) are prominent early events triggered by many G protein-coupled receptors (GPCRs), but the mechanisms involved remain unclear. Here, we examined whether the Rho-associated protein serine/threonine kinase family (ROCK) is a critical Rho effector in the pathway that links GPCR activation to the tyrosine phosphorylation of FAK, CAS, and paxillin. Treatment of Swiss 3T3 cells with Y-27632, a preferential inhibitor of ROCK, dramatically inhibited the formation of actin stress fibers, the assembly of focal contacts, and the increase in tyrosine phosphorylation of FAK and paxillin induced by bombesin in these cells. Surprisingly, we found that treatment with Y-27632 did not produce any detectable effect on bombesin-elicited CAS tyrosine phosphorylation even at the highest concentrations of Y-27632 tested. HA-1077, a preferential inhibitor of ROCK activity structurally unrelated to Y-27632, also attenuated the increase in the tyrosine phosphorylation of FAK and paxillin but did not affect the tyrosine phosphorylation of CAS induced by bombesin in Swiss 3T3 cells. The results demonstrate that ROCK-dependent tyrosine phosphorylation of FAK and paxillin can be dissociated from a ROCK-independent pathway leading to tyrosine phosphorylation of CAS.     

Transient rho-associated coiled-coil containing kinase (ROCK) inhibition on human retinal pigment epithelium results in persistent Rho/ROCK downregulation

Retinal pigment epithelium (RPE) cells is the outermost layer of the retina and RPE dysfunction is a key factor in the disease pathogenesis of age-related macular degeneration (AMD). Transplantation therapy using induced pluripotent stem cell (iPSC)-derived RPEs has recently received much attention as a treatment for AMD. Preserving these cells under the best possible conditions is important, and preservation methods using Y-27632 have been reported. Rho-associated coiled-coil containing kinase (ROCK) inhibitors are known to inhibit cell death, emerging as important drug candidates for stem cell differentiation and regenerative medicine. However, it has recently been shown that ROCK inhibitors may have a vasodilatory effect on human retinal arterioles, a side effect that should ideally be avoided in RPE transplantation. Although ROCK inhibitors hold great potential, optimizing efficacy while minimizing adverse reactions is critical for translation into a clinical treatment. We examined the effect of transient exposure of RPE cells to ROCK inhibitor Y-27632 to determine whether the extracellular presence of the drug is necessary for ongoing Rho/ROCK downregulation. Human RPE cells were subcultured as a suspension for 4 h in drug-free medium following exposure to Y-27632 for 2 h. A Y-27632 concentration of >10 μM improved cell survival beyond 4 h and cell proliferation in recovery culture medium. ROCK2 expression levels were specifically downregulated by Y-27632 in the Rho/ROCK signaling pathway. In conclusion, we demonstrated that the effect of Y-27632 is not dependent on its extracellular availability and can last beyond the 2 h of exposure. The lasting Rho/ROCK signaling pathway downregulation by Y-27632 suggests that RPE cell transplantation with ROCK inhibitor-free media is possible, which can minimize side effects to host tissue and have wider implications for transplantation methods requiring ROCK inhibition.     

Rho/ROCK and Cdk5 effects on phosphorylation of a beta-thymosin repeat protein in Hermissenda

Rho GTPases acting through effector proteins regulate actin dynamics and cytoskeletal structure. In Hermissenda Csp24 is a cytoskeletal-related protein that contributes to the development of intermediate-term memory, and is homologous to other beta-thymosin-like repeat proteins containing multiple actin-binding domains. We have examined the role of Rho GTPase activity and its downstream target ROCK, and cyclin-dependent kinase 5 (Cdk5) on the phosphorylation of Csp24 using 32PO4 labeling of proteins separated with 2-D PAGE. The ROCK inhibitor Y-27632 significantly increased Csp24 phosphorylation, and the Rho activator lysophosphatidic acid (LPA) or the Cdk5 inhibitor butyrolactone significantly decreased Csp24 phosphorylation. Pretreatment with Y-27632 before LPA application significantly reduced the decreased phosphorylation of Csp24 normally detected in nervous systems exposed to LPA. Using a pull-down assay we found that LPA treatments activated Rho and exposure to 5-HT decreased Rho activity. Our results indicate that the Rho/ROCK and Cdk5 signaling pathways contribute to the regulation of Csp24 phosphorylation.     

ROCK and mDia1 antagonize in Rho-dependent Rac activation in Swiss 3T3 fibroblasts

The small GTPase Rho acts on two effectors, ROCK and mDia1, and induces stress fibers and focal adhesions. However, how ROCK and mDia1 individually regulate signals and dynamics of these structures remains unknown. We stimulated serum-starved Swiss 3T3 fibroblasts with LPA and compared the effects of C3 exoenzyme, a Rho inhibitor, with those of Y-27632, a ROCK inhibitor. Y-27632 treatment suppressed LPA-induced formation of stress fibers and focal adhesions as did C3 exoenzyme but induced membrane ruffles and focal complexes, which were absent in the C3 exoenzyme-treated cells. This phenotype was suppressed by expression of N17Rac. Consistently, the amount of GTP-Rac increased significantly by Y-27632 in LPA-stimulated cells. Biochemically, Y-27632 suppressed tyrosine phosphorylation of paxillin and focal adhesion kinase and not that of Cas. Inhibition of Cas phosphorylation with PP1 or expression of a dominant negative Cas mutant inhibited Y-27632-induced membrane ruffle formation. Moreover, Crk-II mutants lacking in binding to either phosphorylated Cas or DOCK180 suppressed the Y-27632-induced membrane ruffle formation. Finally, expression of a dominant negative mDia1 mutant also inhibited the membrane ruffle formation by Y-27632. Thus, these results have revealed the Rho-dependent Rac activation signaling that is mediated by mDia1 through Cas phosphorylation and antagonized by the action of ROCK.     

Selectivity of ROCK inhibitors in the spontaneously tonic smooth muscle

The selectivity of different Rho kinase (ROCK) inhibitors in the spontaneously tonic smooth muscle has not been investigated. We examined this issue using Y-27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarbox anecarboxamide, 2HCl], H-1152 [(S)-(+)-(2-methyl-5-isoquinolinyl) sulfonylhomopiperazine, 2HCl], HA-1077 [(5 isoquinolinesulfonyl) homopiperazine, 2HCl], and ROCK inhibitor II [N-(4-pyridyl)-N'-(2,4,6-trichlorophenyl)urea]. We compared these inhibitors in the spontaneously tonic smooth muscle of the internal anal sphincter (IAS). ROCK, protein kinase C (PKC), and myosin light chain kinase (MLCK) activities were determined in the IAS, before and after different ROCK inhibitors. Y-27632 and H-1152 were approximately 30-fold more potent in the IAS (IC(50): 4.4 x 10(-7) and 7.9 x 10(-8) M, respectively) vs. the phasic rectal smooth muscle (RSM) (IC(50): 1.3 x 10(-5) and 2.5 x 10(-6) M, respectively). HA-1077 and ROCK inhibitor II were equipotent in the IAS vs. RSM. In the IAS, H-1152 was the most potent whereas ROCK inhibitor II is the least. Y-27632 and H-1152 caused concentration-dependent decrease in the IAS tone that correlates directly with the decreases in ROCK activity, without significant effect in the PKC and MLCK activities. This specifically selective correlation between ROCK activity and decrease in the IAS tone was absent in the case of HA-1077 and ROCK inhibitor II, which also inhibited PKC and MLCK. We conclude that the IAS tone is critically dependent on ROCK activity, and H-1152 and Y-27632 are the most selective and potent ROCK inhibitors in the IAS.     

Inhibition of Rho kinase (ROCK) increases neurite outgrowth on chondroitin sulphate proteoglycan in vitro and axonal regeneration in the adult optic nerve in vivo

Inhibitory molecules derived from CNS myelin and glial scar tissue are major causes for insufficient functional regeneration in the mammalian CNS. A multitude of these molecules signal through the Rho/Rho kinase (ROCK) pathway. We evaluated three inhibitors of ROCK, Y- 27632, Fasudil (HA-1077), and Dimethylfasudil (H-1152), in models of neurite outgrowth in vitro. We show, that all three ROCK inhibitors partially restore neurite outgrowth of Ntera-2 neurons on the inhibitory chondroitin sulphate proteoglycan substrate. In the rat optic nerve crush model Y-27632 dose-dependently increased regeneration of retinal ganglion cell axons in vivo. Application of Dimethylfasudil showed a trend towards increased axonal regeneration in an intermediate concentration. We demonstrate that inhibition of ROCK can be an effective therapeutic approach to increase regeneration of CNS neurons. The selection of a suitable inhibitor with a broad therapeutic window, however, is crucial in order to minimize unwanted side effects and to avoid deleterious effects on nerve fiber growth.     

RhoA-Rho kinase pathway mediates thrombin- and U-46619-induced phosphorylation of a myosin phosphatase inhibitor, CPI-17, in vascular smooth muscle cells

Protein kinase C-potentiated phosphatase inhibitor of 17 kDa (CPI-17) mediates some agonist-induced smooth muscle contraction by suppressing the myosin phosphatase in a phosphorylation-dependent manner. The physiologically relevant kinases that phosphorylate CPI-17 remain to be identified. Several previous studies have shown that some agonist-induced CPI-17 phosphorylation in smooth muscle tissues was attenuated by the Rho kinase (ROCK) inhibitor Y-27632, suggesting that ROCK is involved in agonist-induced CPI-17 phosphorylation. However, Y-27632 has recently been found to inhibit protein kinase C (PKC)-, a well-recognized CPI-17 kinase. Thus the role of ROCK in agonist-induced CPI-17 phosphorylation remains uncertain. The present study was designed to address this important issue. We selectively activated the RhoA pathway using inducible adenovirus-mediated expression of a constitutively active mutant RhoA (V14RhoA) in primary cultured rabbit aortic vascular smooth muscle cells (VSMCs). V14RhoA caused expression level-dependent CPI-17 phosphorylation at Thr38 as well as myosin phosphatase phosphorylation at Thr853. Importantly, we have shown that V14RhoA-induced CPI-17 phosphorylation was not affected by the PKC inhibitor GF109203X but was abolished by Y-27632, suggesting that ROCK but not PKC was involved. Furthermore, we have shown that the contractile agonists thrombin and U-46619 induced CPI-17 phosphorylation in VSMCs. Similarly to V14RhoA-induced CPI-17 phosphorylation, thrombin-induced CPI-17 phosphorylation was not affected by inhibition of PKC with GF109203X, but it was blocked by inhibition of RhoA with adenovirus-mediated expression of exoenzyme C3 as well as by Y-27632. Taken together, our present data provide the first clear evidence indicating that ROCK is responsible for thrombin- and U-46619-induced CPI-17 phosphorylation in primary cultured VSMCs. protein kinase C; signal transduction; adenovirus     

Glycine-extended gastrin stimulates cell proliferation and migration through a Rho- and ROCK-dependent pathway, not a Rac/Cdc42-dependent pathway

Both amidated gastrin (Gamide) and glycine-extended gastrin (Ggly) stimulate gastrointestinal cell proliferation and migration. Binding of Gamide to the cholecystokinin-2 receptor activates small GTP-binding proteins of the Rho family (Rho, Rac, and Cdc42), and dominant-negative mutants of Rho or Cdc42 block Gamide-stimulated cell proliferation and survival. In comparison, little is known about the Ggly signaling transduction pathway leading to cell proliferation and migration. The present study examined the roles of the small G proteins Rho, Rac, and Cdc42 in Ggly-induced proliferation and migration of the mouse gastric epithelial cell line IMGE-5. Ggly stimulated the activation of Rho and its downstream effector protein ROCK. The activation of Rho and ROCK mediated Ggly-induced cell proliferation and migration as inhibition of Rho by C3, or ROCK by Y-27632, completely blocked these effects of Ggly. Ggly also stimulated tyrosine phosphorylation of focal adhesion kinase, and stimulation was reversed by addition of C3 and Y-27632. In contrast to the effects of Rho and ROCK, inhibition of the Rac or Cdc42 pathways by expression of dominant-negative mutants of Rac or Cdc42 did not affect Ggly-induced cell proliferation and migration. These results demonstrate that Ggly stimulates IMGE-5 cell proliferation and migration through a Rho/ROCK-dependent pathway but not via Rac- or Cdc42-dependent pathways.     

RhoA induces expression of inflammatory cytokine in adipocytes

Rho GTPase regulates actin cytoskeleton organization and assembly in many cell types, however, its significance in adipose tissue is not well characterized. Here, we demonstrate high RhoA activity in adipose tissues of C57BL/6J mice. To determine the effect of RhoA activation on 3T3-L1 cells, stable cell lines overexpressing G14VRhoA fused to destabilizing domain of FKBP12 (DD-G14VRhoA-L1) were generated. Treatment of DD-G14VRhoA-L1 cells with Shield1 following their differentiation into adipocytes, resulted in the appearance of thick cortical actin filaments, and increased the mRNA expression levels of plasminogen activator inhibitor type-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1). The induction of PAI-1 and MCP-1 was inhibited by treatment with a Rho-associated kinase (ROCK) inhibitor, Y-27632. In 3T3-L1 adipocytes, tumor necrosis factor-α activated RhoA and increased mRNA expression of PAI-1 and MCP-1, and their treatment with Y-27632 partially inhibited these changes. The results indicate that RhoA-ROCK pathway induces inflammatory cytokine expression in adipocytes.     

The suppression of small GTPase rho signal transduction pathway inhibits angiogenesis in vitro and in vivo

Angiogenesis consists of multistep pathways such as the degradation of the matrix, proliferation of the endothelial cells, motility of the endothelial cells, formation of the cord structure and network formation of microvessels. The small GTPase Rho participates in cell motility through actin fiber polymerization. The role of the small GTPase Rho signal transduction pathway in regulating angiogenesis, however, is still unknown. In this study, we investigated the role of the small GTPase Rho signal transduction pathway in angiogenesis in vitro and in vivo using the exoenzyme, Clostridium botulinum C3 transferase, which specifically suppresses Rho and a compound, Y-27632, which suppresses p160ROCK (Rho-associated coiled-coil containing protein kinase). In this paper, we showed that the small GTPase Rho-p160ROCK signal transduction pathway played an important role in angiogenesis both in vitro and in vivo. These results suggest that inhibition of the small GTPase Rho signal transduction pathway by the p160ROCK inhibitor could be a possible new strategy for angiogenic diseases.     

Impact of engagement of FcepsilonRI and CC chemokine receptor 1 on mast cell activation and motility

CC chemokines participate in the recruitment and activation of immune cells through CC chemokine receptors (CCRs). Here, we report that cross-talk between CCR1-mediated signaling pathway and FcepsilonRI-mediated signaling pathway affects degranulation positively but affects chemotaxis of mast cells adversely. Costimulation via FcepsilonRI engagement with IgE/antigen and CCR1 engagement with recombinant human CCL3 synergistically enhanced degranulation in rat basophilic leukemia-2H3 cells expressing human CCR1 (RBL-CCR1). Interestingly, FcepsilonRI engagement inhibited CCL3-mediated chemotaxis and membrane ruffling of RBL-CCR1 cells. Small GTP-binding proteins of the Rho family, Rac, Cdc42, and Rho control chemotaxis by mediating the reorganization of the actin cytoskeleton. Both a Rho inhibitor C3 exoenzyme and a Rho kinase (ROCK) inhibitor Y-27632 inhibited chemotaxis of RBL-CCR1 cells toward CCL3, indicating that activation of the Rho/ROCK signaling pathway is required for the CCL3-mediated chemotaxis of the cells. Costimulation with IgE/antigen and CCL3 enhanced Rac and Cdc42 activation but decreased ROCK activation in RBL-CCR1 cells compared with that in the cells stimulated with CCL3 alone. These results suggest that costimulation via FcepsilonRI and CCR1 engagements induced 1) inhibition of membrane ruffling, 2) decreased ROCK activation, and 3) reciprocal imbalance between Small GTP-binding proteins of the Rho family, which result in the inhibition of chemotaxis of RBL-CCR1 cells. The cross-talk between FcepsilonRI-mediated signaling pathway and CCR-mediated signaling pathway would induce optimal activation and arrested chemotaxis of mast cells, thus contributing to allergic inflammation.     

Role of Rho-kinase in reexpansion pulmonary edema in rabbits

Reexpansion of a collapsed lung increases the microvascular permeability and causes reexpansion pulmonary edema. Neutrophils and their products have been implicated in the development of this phenomenon. The small GTP-binding proteins Rho and its target Rho-kinase (ROCK) regulate endothelial permeability, although their roles in reexpansion pulmonary edema remain unclear. We studied the contribution of ROCK to pulmonary endothelial and epithelial permeability in a rabbit model of this disorder. Endothelial and epithelial permeability was assessed by measuring the tissue-to-plasma (T/P) and bronchoalveolar lavage (BAL) fluid-to-plasma (B/P) ratios with (125)I-labeled albumin. After intratracheal instillation of (125)I-albumin, epithelial permeability was also assessed from the plasma leak (PL) index, the ratio of (125)I-albumin in plasma/total amount of instilled (125)I-albumin. T/P, B/P, and PL index were significantly increased in the reexpanded lung. These increases were attenuated by pretreatment with Y-27632, a specific ROCK inhibitor. However, neutrophil influx, neutrophil elastase activity, and malondialdehyde concentrations in BAL fluid collected from the reexpanded lung were not changed by Y-27632. In endothelial monolayers, Y-27632 significantly attenuated the H(2)O(2)-induced increase in permeability and mitigated the morphological changes in the actin microfilament cytoskeleton of endothelial cells. These in vivo and in vitro observations suggest that the Rho/ROCK pathway contributes to the increase in alveolar barrier permeability associated with reexpansion pulmonary edema.     

Polarization and Migration of Hematopoietic Stem and Progenitor Cells Rely on the RhoA/ROCK I Pathway and an Active Reorganization of the Microtubule Network

Understanding the physiological migration of hematopoietic progenitors is important, not only for basic stem cell research, but also in view of their therapeutic relevance. Here, we investigated the role of the Rho kinase pathway in the morphology and migration of hematopoietic progenitors using an ex vivo co-culture consisting of human primary CD34⁺ progenitors and mesenchymal stromal cells. The addition of the Rho kinase inhibitor Y-27632 led to the abolishment of the uropod and microvillar-like structures of hematopoietic progenitors, concomitant with a redistribution of proteins found therein (prominin-1 and ezrin). Y-27632-treated cells displayed a deficiency in migration. Time-lapse video microscopy revealed impairment of the rear pole retraction. Interestingly, the knockdown of ROCK I, but not ROCK II, using RNA interference (RNAi) was sufficient to cause the referred morphological and migrational changes. Unexpectedly, the addition of nocodazole to either Y-27632- or ROCK I RNAi-treated cells could restore their polarized morphology and migration suggesting an active role for the microtubule network in tail retraction. Finally, we could demonstrate using RNAi that RhoA, the upstream regulator of ROCK, is involved in these processes. Collectively, our data provide new insights regarding the role of RhoA/ROCK I and the microtubules in the migration of stem cells.