YB-1 Is Important for an Early Stage Embryonic Development

Abstract

The eukaryotic Y-box-binding protein-1 (YB-1) is involved in the transcriptional and translational control of many biological processes, including cell proliferation. In clinical studies, the cellular level of YB-1 closely correlates with tumor growth and prognosis. To understand the role of YB-1 in vivo, especially in the developmental process, we generated YB-1 knock-out mice, which are embryonic lethal and exhibit exencephaly associated with abnormal patterns of cell proliferation within the neuroepithelium. β-Actin expression and F-actin formation were reduced in the YB-1 null embryo and YB-1-/- mouse embryonic fibroblasts, suggesting that the neural tube defect is caused by abnormal cell morphology and actin assembly within the neuroepithelium. Fibroblasts derived from YB-1-/- embryos demonstrated reduced growth and cell density. A colony formation assay showed that YB-1-/- mouse embryonic fibroblasts failed to undergo morphological transformation and remained contact-inhibited in culture. These results demonstrate that YB-1 is involved in early mouse development, including neural tube closure and cell proliferation. The eukaryotic Y-box-binding protein-1 (YB-1) is involved in the transcriptional and translational control of many biological processes, including cell proliferation. In clinical studies, the cellular level of YB-1 closely correlates with tumor growth and prognosis. To understand the role of YB-1 in vivo, especially in the developmental process, we generated YB-1 knock-out mice, which are embryonic lethal and exhibit exencephaly associated with abnormal patterns of cell proliferation within the neuroepithelium. β-Actin expression and F-actin formation were reduced in the YB-1 null embryo and YB-1-/- mouse embryonic fibroblasts, suggesting that the neural tube defect is caused by abnormal cell morphology and actin assembly within the neuroepithelium. Fibroblasts derived from YB-1-/- embryos demonstrated reduced growth and cell density. A colony formation assay showed that YB-1-/- mouse embryonic fibroblasts failed to undergo morphological transformation and remained contact-inhibited in culture. These results demonstrate that YB-1 is involved in early mouse development, including neural tube closure and cell proliferation. The Y-box protein family is characterized by a highly conserved cold-shock domain that binds nucleic acids and shares homology with the prokaryotic cold-shock proteins (1Makino Y. Ohga T. Toh S. Koike K. Okumura K. Wada M. Kuwano M. Kohno K. Nucleic Acids Res. 1996; 24: 1873-1878Crossref PubMed Scopus (39) Google Scholar, 2Kohno K. Izumi H. Uchiumi T. Ashizuka M. Kuwano M. BioEssays. 2003; 25: 691-698Crossref PubMed Scopus (435) Google Scholar). The human Y-boxbinding gene, YB-1, is located on chromosome 1p34 (1Makino Y. Ohga T. Toh S. Koike K. Okumura K. Wada M. Kuwano M. Kohno K. Nucleic Acids Res. 1996; 24: 1873-1878Crossref PubMed Scopus (39) Google Scholar). YB-1 has multiple functions but was initially identified as a transcription factor that associates with the Y-box sequence of the major histocompatibility complex class II genes (3Didier D.K. Schiffenbauer J. Woulfe S.L. Zacheis M. Schwartz B.D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 7322-7326Crossref PubMed Scopus (359) Google Scholar). YB-1 promotes cell proliferation through its transcriptional regulation of target genes such as proliferating cell nuclear antigen (PCNA), 2The abbreviations used are: PCNA, proliferating cell nuclear antigen; MEF, mouse embryonic fibroblasts; PBS, phosphate-buffered saline; siRNA, small interfering RNA; FITC, fluorescein isothiocyanate; PI3K, phosphatidylinositol 3-kinase; NTD, neural tube defect; E, embryonic day; S6K, p70 S6K. epidermal growth factor receptor, DNA topoisomerase IIα, thymidine kinase, and DNA polymerase α (4Ladomery M. Sommerville J. BioEssays. 1995; 17: 9-11Crossref PubMed Scopus (130) Google Scholar, 5Kohno K. Uchiumi T. Niina I. Wakasugi T. Igarashi T. Momii Y. Yoshida T. Matsuo K. Miyamoto N. Izumi H. Eur. J. Cancer. 2005; 41: 2577-2586Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar). We previously reported its role in the transcriptional activation of human multidrug resistance 1 (MDR1) and DNA topoisomerase IIα in response to various environmental stimuli (6Asakuno K. Kohno K. Uchiumi T. Kubo T. Sato S. Isono M. Kuwano M. Biochem. Biophys. Res. Commun. 1994; 199: 1428-1435Crossref PubMed Scopus (75) Google Scholar, 7Ohga T. Uchiumi T. Makino Y. Koike K. Wada M. Kuwano M. Kohno K. J. Biol. Chem. 1998; 273: 5997-6000Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar). In addition, it has been shown to chaperone RNA, modify chromatin, participate in the translational masking of mRNA, and be involved in stress responses such as the redox signaling pathway (8Swamynathan S.K. Nambiar A. Guntaka R.V. FASEB J. 1998; 12: 515-522Crossref PubMed Scopus (87) Google Scholar). Eukaryotic Y-box proteins also regulate gene expression at the translational level through their recognition of RNA (9Sommerville J. BioEssays. 1999; 21: 319-325Crossref PubMed Scopus (144) Google Scholar, 10Ashizuka M. Fukuda T. Nakamura T. Shirasuna K. Iwai K. Izumi H. Kohno K. Kuwano M. Uchiumi T. Mol. Cell. Biol. 2002; 22: 6375-6383Crossref PubMed Scopus (52) Google Scholar, 11Fukuda T. Ashizuka M. Nakamura T. Shibahara K. Maeda K. Izumi H. Kohno K. Kuwano M. Uchiumi T. Nucleic Acids Res. 2004; 32: 611-622Crossref PubMed Scopus (32) Google Scholar), and therefore play critical roles in both mRNA turnover and translational control. YB-1 protects mammalian cells from the cytotoxic effects induced by DNA damage. We previously reported that human cancer cell lines overexpressing YB-1 resist cisplatin, whereas the reduction of YB-1 itself leads to increased sensitivity to cisplatin, other DNA-interacting drugs, and UV irradiation (2Kohno K. Izumi H. Uchiumi T. Ashizuka M. Kuwano M. BioEssays. 2003; 25: 691-698Crossref PubMed Scopus (435) Google Scholar). YB-1 is mainly localized in the cytoplasm, but translocates to the nucleus following UV irradiation of cells or treatment with anticancer drugs (12Koike K. Uchiumi T. Ohga T. Toh S. Wada M. Kohno K. Kuwano M. FEBS Lett. 1997; 417: 390-394Crossref PubMed Scopus (176) Google Scholar). YB-1 binds directly to repair-associated proteins such as PCNA and p53 (13Okamoto T. Izumi H. Imamura T. Takano H. Ise T. Uchiumi T. Kuwano M. Kohno K. Oncogene. 2000; 19: 6194-6202Crossref PubMed Scopus (134) Google Scholar), whereas proteolytic cleavage of the C-terminal fragment is linked to stress induced by DNA damage (14Sorokin A.V. Selyutina A.A. Skabkin M.A. Guryanov S.G. Nazimov I.V. Richard C. Th'ng J. Yau J. Sorensen P.H. Ovchinnikov L.P. Evdokimova V. EMBO J. 2005; 24: 3602-3612Crossref PubMed Scopus (127) Google Scholar). In clinical studies, the cellular level of YB-1 has been shown to correlate with tumor growth and prognosis in cancers of the ovary, lung, and breast (15Kuwano M. Oda Y. Izumi H. Yang S.J. Uchiumi T. Iwamoto Y. Toi M. Fujii T. Yamana H. Kinoshita H. Kamura T. Tsuneyoshi M. Yasumoto K. Kohno K. Mol. Cancer Ther. 2004; 3: 1485-1492PubMed Google Scholar). Moreover, overexpression or the nuclear presence or absence of YB-1 plays a critical role in P-glycoprotein expression, malignant progression, poor prognosis, and global drug resistance (2Kohno K. Izumi H. Uchiumi T. Ashizuka M. Kuwano M. BioEssays. 2003; 25: 691-698Crossref PubMed Scopus (435) Google Scholar, 15Kuwano M. Oda Y. Izumi H. Yang S.J. Uchiumi T. Iwamoto Y. Toi M. Fujii T. Yamana H. Kinoshita H. Kamura T. Tsuneyoshi M. Yasumoto K. Kohno K. Mol. Cancer Ther. 2004; 3: 1485-1492PubMed Google Scholar, 16Torigoe T. Izumi H. Ishiguchi H. Yoshida Y. Tanabe M. Yoshida T. Igarashi T. Niina I. Wakasugi T. Imaizumi T. Momii Y. Kuwano M. Kohno K. Curr. Med. Chem. Anticancer Agents. 2005; 5: 15-27Crossref PubMed Scopus (105) Google Scholar). To understand how YB-1 proteins exert their multiple functions, we previously established mouse embryonic stem cell lines with a heterozygously targeted disruption of the YB-1 gene (YB-1+/-), and we demonstrated their hypersensitivity to cytotoxic agents such as cisplatin and mitomycin C (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google Scholar). Here we carried out targeted disruptions of the mouse YB-1 gene to elucidate the role of YB-1 molecules in vivo. We show that YB-1 plays a critical role in early development in mice. The targeted disruptions were fatal in the late embryonic stage, and animals showed defects in the anterior neural tube. Furthermore, we investigated the role of YB-1 in cell proliferation and the transformation activity of MEFs. Animals—Animals were mated overnight, and the females were examined for a vaginal plug the following morning. Noon on the day of vaginal plug detection was recorded as day E0.5. All animal experiments were carried out according to the guidelines for animal experimentation at Kyushu University, Japan, and the University of Occupational Environmental Health, Japan. All experimental protocols were approved by the ethics committee of Kyushu University and the University of Occupational Environmental Health, Japan. In Situ Hybridization—In situ hybridization of digoxygeninlabeled probes was performed as described previously (18Yoshida S. Ohbo K. Takakura A. Takebayashi H. Okada T. Abe K. Nabeshima Y. Dev. Biol. 2001; 240: 517-530Crossref PubMed Scopus (57) Google Scholar). The digoxigenin-labeled hybridization probe was prepared from an in vitro transcription system (Promega, Madison, WI) using the mouse YB-1 full-length cDNA (11Fukuda T. Ashizuka M. Nakamura T. Shibahara K. Maeda K. Izumi H. Kohno K. Kuwano M. Uchiumi T. Nucleic Acids Res. 2004; 32: 611-622Crossref PubMed Scopus (32) Google Scholar). Generation of YB-1 (MSY-1)-deficient Mice—Embryonic stem cells were transfected with the linearized targeting construct that deleted exons 5 and 6 of mouse YB-1 (MSY-1) (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google Scholar), and recombinant clones were selected and microinjected into C57BL/6 mouse blastocytes. Chimeric males that transmitted the mutant allele to the germ line were mated with C57BL/6 females, and germ line transmission of the mutant allele was confirmed by Southern blot analysis (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google Scholar). Heterozygous offspring were intercrossed to produce homozygous mutant animals. For embryo genotyping, DNA was extracted from the corresponding embryonic tissue removed from microscope sections and amplified by 30 cycles of PCR at 94 °C for 30 s, 58 °C for 30 s, and 68 °C for 1 min using the following primers: YB5-1, 5′-GGAAACCATGTGGAGATGTC, and YB3-1, 5′-GGAGGTTCAAAAGCACACTC (wild-type allele); neo5, 5′-GATTGCACGCAGGTTCTCCG, and neo3, 5′-CAAGAAGGCGATAGAAGGCG (mutant allele). Immunohistochemistry—Cells seeded the previous day on glass coverslips were washed with phosphate-buffered saline (PBS), fixed with 3.7% formaldehyde for 30 min, rinsed twice with PBS, and then incubated with PBS containing 0.1% Triton X-100 (Sigma) for 30 min. Next, the coverslips were washed with PBS, incubated with 10% goat serum for 1 h at room temperature in a humidified container, and then incubated for 1 h with FITC-conjugated phalloidin (Sigma). After washing three times with PBS, glass slides were mounted using Slowfade mounting FITC-conjugated phalloidin (Sigma) was and used to F-actin in mouse tissue and and cells were with 1 0.1% and and to analysis as described previously (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google using YB-1 T. Koike K. M. Makino Y. Y. M. Kuwano M. Kohno K. Cancer Res. 1996; Google and p70 and PCNA were by of embryo tissue was fixed with 10% and in sections were and mounted on glass After and through the slides were for min to the activity was using by three in PBS containing Triton and the sections were with 10% goat serum in were incubated for 1 h with the YB-1 and in PBS containing Triton X-100 and 0.1% serum by three in PBS, and then with the FITC-conjugated goat for 30 min. were with for 30 and washed with The sections were by in and then mounted with and were using a microscope with a of Fibroblasts and mutant were to (YB-1+/-), and homozygous mutant embryonic fibroblasts were in with 10% were and their development was by were seeded in in and serum were and using a cell were seeded in in and in with 10% serum and was After transformation was by All transformation were at three were with and in was in prepared with a of with containing 5 were with were with and with cells were on an microscope were performed according to the cells in were transfected with RNA control and YB-1 at a of using After cell and cell were using an with a cell were also for (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google Scholar). of YB-1 elucidate the of YB-1 mouse development, we used gene targeting to mice. the offspring and Southern blot analysis of DNA from that animals from were homozygous for the YB-1 of YB-1 results in embryonic embryonic in a To the at which the YB-1 mutant we examined embryos from at various developmental PCR of mouse embryos at and homozygous in with the and confirmed by PCR with In to the growth of YB-1-/- embryos as early as YB-1-/- embryos been by and YB-1-/- embryos and The of YB-1-/- embryos and but is in YB-1 in reported previously that human YB-1 is in the T. Koike K. M. Makino Y. Y. M. Kuwano M. Kohno K. Cancer Res. 1996; Google Scholar). The YB-1 and protein also been in mouse embryonic stem cells (17Shibahara K. Uchiumi T. Fukuda T. Kura S. Tominaga Y. Maehara Y. Kohno K. Nakabeppu Y. Tsuzuki T. Kuwano M. Cancer Sci. 2004; 95: 348-353Crossref PubMed Scopus (41) Google Scholar). To the expression of mouse YB-1 is we performed in situ hybridization on mouse embryos tissue sections at We that mouse YB-1 mRNA is at at in the A and in the is with in the of the and into and YB-1 mRNA is also in the the and in the These a critical role for YB-1 expression embryonic YB-1 protein expression in embryos is with expression in the lung, and YB-1 was localized to the in expression was in or of embryos and was from YB-1-/- embryos in shown in YB-1-/- embryos were their were in or examined at to of the YB-1-/- embryos exencephaly in the and YB-1-/- of the mutant embryos were and as a of through as and patterns in analysis of other of the mutant embryos that the YB-1 major were a defect in closure of the anterior neural which and A. Mol. 2000; PubMed Scopus (57) Google Scholar). showed a characterized by and a of embryos to that the mutant failed to and of the of the to neural tube defect embryos demonstrate neural tube closure and and the anterior neural of to YB-1-/- embryos failed to with of other or neural tube such as or neural closure were YB-1-/- that closure also major but demonstrated development of the and YB-1-/- embryos a of the which was in and mice. Moreover, of YB-1-/- embryos were of their and which is of YB-1-/- embryos were also as a of defects in of the These that of and for the embryonic of the YB-1 in YB-1-/- of mouse embryos and YB-1-/- the expression of other proteins involved in the regulation of was examined by using the YB-1 and C-terminal that YB-1-/- embryos the full-length or the YB-1 protein embryos as YB-1 as The expression of the protein p70 was reduced in YB-1 null embryos with and whereas human eukaryotic factor and PCNA expression was translational was in YB-1-/- which a in YB-1-/- the of YB-1 in cellular we established from and YB-1-/- embryos from three at Heterozygous and as YB-1 as whereas YB-1 null and PCNA expression was the three cell proliferation and was and YB-1-/- MEFs. to 5 YB-1-/- showed reduced proliferation and a reduction in cell and at a YB-1-/- and an as by an and cell morphology After of YB-1-/- cells showed reduced cell proliferation and which be to by expression of the YB-1 YB-1 expression from was confirmed by These demonstrate the of YB-1 in cell proliferation and cell and in genes that regulate actin at the cell or play roles in actin been reported previously 1999; PubMed Scopus Google Scholar). In the defects exencephaly caused by a of neural as in the YB-1-/- In addition, YB-1 has been shown to with mRNA and the actin protein (11Fukuda T. Ashizuka M. Nakamura T. Shibahara K. Maeda K. Izumi H. Kohno K. Kuwano M. Uchiumi T. Nucleic Acids Res. 2004; 32: 611-622Crossref PubMed Scopus (32) Google Scholar, Evdokimova Ovchinnikov L.P. J. Sci. 1999; Google Scholar). We used to and are in YB-1-/- and we showed that protein were reduced in the of the YB-1 null in with the of sections a of F-actin the of cells in the null mutant embryo with the These that the reduced and F-actin formation be for the of YB-1-/- In mutant a reduced of the cells within was also We examined the role of YB-1 in cell morphology and of the actin an morphology and an In YB-1-/- were in with cell mutant cells F-actin such as or a small of F-actin was as a phalloidin that was in the in the cell These results show that YB-1 is for F-actin and the cell of MEFs. YB-1 RNA activity and has been shown to regulate protein and mRNA (11Fukuda T. Ashizuka M. Nakamura T. Shibahara K. Maeda K. Izumi H. Kohno K. Kuwano M. Uchiumi T. Nucleic Acids Res. 2004; 32: 611-622Crossref PubMed Scopus (32) Google Scholar, K. M. M. Dev. 2000; PubMed Google Scholar), we investigated the of YB-1 with in vitro RNA assay was performed using recombinant YB-1 and a probe corresponding to full-length YB-1 to mRNA, whereas the control protein failed to To the in vivo, we performed using on mRNA by with β-Actin was amplified from but from YB-1-/- suggesting that YB-1 with mRNA in MEFs. regulate the activity or of in protein by YB-1-/- established three and three YB-1-/- lines for 6 to their transformation in the cells show of a in YB-1-/- failed to undergo morphological transformation and remained contact-inhibited of and of YB-1, the morphological whereas failed to Furthermore, a reduction in growth was in the YB-1-/- clones To we investigated of YB-1 cell growth and The was the YB-1 C-terminal with the of the cold-shock blot analysis of that YB-1 protein were reduced to of h YB-1 also showed a reduced growth and were in the control transfected in and was with of YB-1-/- and that YB-1 is involved in both cell growth and cell In an transformation assay in YB-1 showed morphological but demonstrated reduced transformation activity These results that YB-1 is for transformation activity also that YB-1 plays a critical role in DNA mRNA and translational control. Mol. Cell. Biol. 2005; 25: PubMed Scopus Google reported that targeted disruption of YB-1 of the cold-shock embryonic and showed that YB-1 is for cellular stress responses and of In we demonstrated that YB-1-/- embryos exhibit growth and a role for YB-1 in early embryonic YB-1 exons 5 and a RNA of the blot analysis using an the YB-1 C that the YB-1 protein was from the YB-1-/- embryo In we demonstrated that expression and F-actin formation were reduced in the YB-1 null embryo and YB-1-/- MEF, suggesting that the neural tube defect is caused by abnormal cell morphology and actin assembly within the neuroepithelium. We also showed that YB-1-/- failed to undergo morphological transformation in cells and that YB-1 is involved in cell proliferation. of YB-1 null mutant showed exencephaly is an as mouse embryos to of a critical gene show with Mol. 2000; PubMed Scopus Google Scholar). an exencephaly the of neural in 1997; PubMed Scopus Google Scholar). The genes in mouse that are involved in actin regulation the role for actin in neural and that the are caused by an absence of the by the of actin Mol. 2000; PubMed Scopus Google Scholar). We that YB-1 of the in a system results been reported for K. M. Mol. Cell. Biol. 2005; 25: PubMed Scopus Google and M.A. A.V. I.V. Ovchinnikov L.P. Nucleic Acids Res. 2004; 32: PubMed Scopus Google Scholar). The in vitro of YB-1 to mRNA Ovchinnikov L.P. J. Biochem. Biol. 1999; PubMed Scopus Google and is a for actin activity or its in protein is with that disruption of YB-1 leads to and reduced actin assembly the of mRNA to of actin has been shown to cell and S. M. J. M. J. 2005; PubMed Scopus Google Scholar). the protein protein 1 which promotes of the to in fibroblasts and associates with the in the nucleus and in the by K. M. Mol. Cell. Biol. 2005; 25: PubMed Scopus Google reported an YB-1 and suggesting that both proteins in their regulation of mRNA and protein at the of the of the The role of YB-1 in cell proliferation be through its with actin Evdokimova Ovchinnikov L.P. J. Sci. 1999; Google Scholar), as actin the that the cell Curr. Biol. 2004; PubMed Scopus Google Scholar). cell proliferation be by the of YB-1 on the cell proteins A and as YB-1 was to of protein in the K. S. U. M. I. M. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus (176) Google Scholar). The targeted disruption of allele of the Y-box protein gene in cells results in major defects in the cell S.K. Guntaka R.V. Biochem. Biophys. Res. Commun. 2002; PubMed Scopus Google Scholar). In in A and expression was in YB-1-/- mouse embryos or suggesting that the expression level of proteins the embryonic and of the YB-1-/- mice. S. K. M. Cancer Res. 2005; PubMed Scopus Google showed that human YB-1 breast through the of caused by and We the transformation of but showed that YB-1-/- failed to undergo morphological transformation and remained contact-inhibited of YB-1 the transformation activity suggesting that YB-1 is for tumor overexpression of YB-1 mRNA and protein is a of human malignant (2Kohno K. Izumi H. Uchiumi T. Ashizuka M. Kuwano M. BioEssays. 2003; 25: 691-698Crossref PubMed Scopus (435) Google Scholar, S. K. M. Cancer Res. 2005; PubMed Scopus Google Scholar), whereas the level of YB-1 protein expression has been linked with the prognosis of breast cancer and resistance to agents K. Uchiumi T. Niina I. Wakasugi T. Igarashi T. Momii Y. Yoshida T. Matsuo K. Miyamoto N. Izumi H. Eur. J. Cancer. 2005; 41: 2577-2586Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar). The nuclear of YB-1 by the protein J. J. C. S. C. M. H. K. S. C. M. Oncogene. 2005; 24: PubMed Scopus Google Scholar), which plays a role in tumor formation and Evdokimova V. A.V. Ovchinnikov L.P. J. N. Sorensen P.H. Mol. Cell. Biol. PubMed Scopus Google reported that by also the of YB-1 with the of mRNA and that translational of We investigated the level of protein in and YB-1 but was and suggesting that YB-1 protein in MEFs. of is a in the signaling pathway that and factor protein N. N. Dev. 2004; PubMed Scopus Google Scholar). We also that protein were reduced in YB-1 null mouse suggesting that YB-1 be involved in signaling YB-1 is in and cells Ovchinnikov L.P. J. Biochem. Biol. 1999; PubMed Scopus Google Scholar, Evdokimova A.A. Ovchinnikov L.P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). YB-1 of the target of as the of and are in cells N. Proc. Natl. Acad. Sci. U. S. A. 2003; PubMed Scopus (57) Google Scholar). line of has the role of protein in and transformation Mol. Cell. Biol. 2005; 25: PubMed Scopus Google Scholar). of eukaryotic factor through by J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, Mol. Biol. 2001; PubMed Scopus Google it to to actin and regulate its activity or its in protein J. Y. J. J. J. J. Sci. 1996; Google Scholar, Mol. Biol. 2005; 12: PubMed Scopus Google Scholar). defects in cell the actin and actin Mol. Biol. 2005; 12: PubMed Scopus Google Scholar). In mammalian disruption of the actin results in reduced In we that YB-1 with suggesting that for the of YB-1 in YB-1-/- embryos and MEFs. We also that translational was in YB-1-/- embryos and YB-1 and of an In we described the of YB-1 in the mouse embryo and in MEFs. We show that it is involved in mouse embryo development, neural tube and cell proliferation. with