There's more to magic than meets the eye

Gustav Kuhn; Michael F Land

doi:10.1016/j.cub.2006.10.012

Nov 1, 2006
Current Biology
Gustav Kuhn +1 more

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Our perception of an event is often modulated by our past experience and expectations [1Ramachandran V.S. Armel C. Foster C. Stoddard R. Object recognition can drive motion perception.Nature. 1998; 395: 852-853Crossref PubMed Scopus (35) Google Scholar, 2O'Regan J.K. Noe A. A sensorimotor account of vision and visual consciousness.Behav. Brain Sci. 2001; 24: 939-973Crossref PubMed Scopus (1863) Google Scholar]. Here we used a magic trick [3Triplett N. The psychology of conjuring deceptions.Am. J. Psychol. 1900; 6: 439-510Crossref Google Scholar] to demonstrate how magicians can distort our subjective perception and we investigate the mechanisms behind this deception. We found that when a magician performed an illusion in which a ball was seen to vanish in the air, 63% of observers perceived the ball leave his hand, move upwards, and disappear even though the ball did not leave the magician's hand. Moreover, observers' illusory perception of the ball was determined by cues that indicated the ball's location, namely the magician's head direction, rather than the percept itself. Furthermore, eye movement records revealed participants' strategic use of social cues prior to looking at the ball. Surprisingly, however, when the ball was not physically present, observers did not look at the area where they claimed to have seen the ball vanish, suggesting that the oculomotor system was not fooled by the illusion. These results show that although people's subjective percept is determined by expectations, the oculomotor system is largely driven by accurate bottom-up information, which is consistent with the suggestion that there are separate mechanisms for perception and visuomotor control [4Goodale M.A. Milner A.D. Separate visual pathways for perception and action.Trends Neurosci. 1992; 15: 20-25Abstract Full Text PDF PubMed Scopus (3924) Google Scholar]. A striking example of magicians' deception is the vanishing ball illusion, in which a ball apparently disappears in mid air. This illusion is created by pretending to throw a ball up in the air, when in fact it remains secretly palmed in the magician's hand [3Triplett N. The psychology of conjuring deceptions.Am. J. Psychol. 1900; 6: 439-510Crossref Google Scholar]. If done convincingly, the observer should perceive the ball as moving up in the air even though it is no longer physically present. Similarly, when observers view a moving object that suddenly disappears, the final position of the object is usually perceived as being further along the path of motion than its actual final position [5Freyd J.J. Finke R.A. Representational Momentum.J. Exp. Psychol. Learn. Mem. Cogn. 1984; 10: 126-132Crossref Scopus (464) Google Scholar], a phenomenon known as representational momentum [6Assad J.A. Maunsell J.H.R. Neuronal correlates of inferred motion in primate posterior parietal carter.Nature. 1995; 373: 518-521Crossref PubMed Scopus (181) Google Scholar]. Much of the magician's deception relies on social cuing, in terms of his head and gaze direction, and we therefore predicted that the effectiveness of the vanishing ball illusion would be influenced by the magician's social cuing. Two different versions of the trick were created that addressed the extent to which the magician's social cues are responsible for the illusion. In the social cues pro-illusion condition, on the final 'fake' throw, the magician's eyes and head followed an imaginary ball moving upwards (Figure 1 and Supplemental data available on-line with this issue). In the social cues anti-illusion condition, the magic trick was identical except that on the final 'fake' throw, the magician looked at the hand concealing the ball, rather than following the imaginary ball (see Figure 2F). We also measured people's eye movements while they watched the video of the trick, to gain an online measure of the information obtained by the visual system. Immediately after having seen the magic trick, participants were questioned as to whether they perceived the 'illusory ball' moving towards the top of the screen on the final throw.Figure 2Participants' fixation points for the social cues pro-illusion (top row) and the social cues anti-illusion (bottom row) conditions.Show full captionThe dots represent the fixation points for the participants who experienced the illusion and the 'X' marks the fixation points for participants who did not experience the illusion. (A,D) At the point when the ball reached its zenith on the first throw. (B,E) at the point when the ball reached its zenith on the second throw. (C,F) At the point when the ball disappeared. For each participant the height of the terminal eye position on the monitor was calculated (distance between the fixation point and the bottom of the monitor, monitor height = 25°); each panel shows the means (M) and standard deviations (SD) for participants who experienced the illusion and those who did not. On the final throw (C,F) there was no significant difference between the final eye position of the participants who perceived the illusion compared to those who did not perceive it (t(36) < 1), which shows that participants' eye movements were not correlated with the perception of the illusion. On the final throw there was no significant difference in the terminal eye positions between the anti- and the pro-illusion condition (t(36) < 1), illustrating that participants' eye movements were not driven by the social cues. 19 participants experienced the illusion. For these participants the terminal eye position on the final throw was significantly lower than on the first (t(18) = 3.23, p = 0.005) and the second throw (t(18) = 3.57, p = 0.002).View Large Image Figure ViewerDownload Hi-res image Download (PPT) The dots represent the fixation points for the participants who experienced the illusion and the 'X' marks the fixation points for participants who did not experience the illusion. (A,D) At the point when the ball reached its zenith on the first throw. (B,E) at the point when the ball reached its zenith on the second throw. (C,F) At the point when the ball disappeared. For each participant the height of the terminal eye position on the monitor was calculated (distance between the fixation point and the bottom of the monitor, monitor height = 25°); each panel shows the means (M) and standard deviations (SD) for participants who experienced the illusion and those who did not. On the final throw (C,F) there was no significant difference between the final eye position of the participants who perceived the illusion compared to those who did not perceive it (t(36) < 1), which shows that participants' eye movements were not correlated with the perception of the illusion. On the final throw there was no significant difference in the terminal eye positions between the anti- and the pro-illusion condition (t(36) < 1), illustrating that participants' eye movements were not driven by the social cues. 19 participants experienced the illusion. For these participants the terminal eye position on the final throw was significantly lower than on the first (t(18) = 3.23, p = 0.005) and the second throw (t(18) = 3.57, p = 0.002). Participants who perceived the illusory ball had a vivid recollection of seeing the ball leave the screen at the top, and typically claimed that the illusion was created by someone catching it beyond the top of the screen. 68% of the participants in the social cues pro-illusion condition experienced the illusion, significantly more than in the social cues anti-illusion condition (32%, χ2 = 5.16, p = 0.025), thus demonstrating that the illusion was mediated by the social cuing. Most of the participants claimed that they spent their entire time looking at the ball. However, these reports deviated strongly from where they were actually looking. Figure 1 shows a timeline indicating where participants were looking during the magic trick. We found a very high consistency in the eye movement patterns between the participants, suggesting that people employed similar eye movement strategies. On throws where the ball was visible, participants generally looked at the ball once it reached the apex. But rather than merely tracking the ball, most of the participants glanced at the magician's face before looking at the ball, indicating that the visual system uses information about where the magician is looking as a way of predicting the location of the ball. Our results show that an observer's percept was driven by the magician's social cuing, and that participants utilized the magician's social cues. However, there was a surprising difference in the susceptibility of these two systems to the illusion. On the final illusory throw, most participants claimed to have seen the ball at the top of the screen. The oculomotor system on the other hand was not fooled by the illusion. Figure 2 shows that participants only looked at the top of the screen when the ball was physically present. These results illustrate a remarkable dissociation between what participants claimed to have seen and the way in which their eyes behaved. Whilst their percept was predominantly based on expectations, their eyes were largely driven by the actual visual input. Our results offer a striking example of how the dissociation between vision for perception and for action, well documented in neurological patients [4Goodale M.A. Milner A.D. Separate visual pathways for perception and action.Trends Neurosci. 1992; 15: 20-25Abstract Full Text PDF PubMed Scopus (3924) Google Scholar, 7Goodale M.A. Haffenden A. Frames of reference for perception and action in the human visual system.Neurosci. Biobehav. Rev. 1998; 22: 161-172Crossref PubMed Scopus (110) Google Scholar, 8Milner A.D. Goodale M.A. The Visual Brain in Action. Oxford University Press, Oxford1995Google Scholar] and neurologically intact subjects [9Aglioti S. Desouza J.F.X. Goodale M.A. Size-contrast illusions deceive the eye but not the hand.Curr. Biol. 1995; 5: 679-685Abstract Full Text Full Text PDF PubMed Scopus (721) Google Scholar], also translates to more real world situations. We would like to thank the reviewers and Cristiana Cavina-Pratesi for their valuable comments on the manuscript, and Tim Smith for his help with a control experiment. Download .pdf (.1 MB) Help with pdf files Document S1. Supplemental Experimental Procedures Download .mpg (1.09 MB) Help with mpg files Movie 1 Vanishing ball trick pro-illusion condition Download .mpg (1.12 MB) Help with mpg files Movie 2 Vanishing ball trick anti-illusion condition

Research Article
42
10.1074/jbc.m109.092676

Identification of Multiple Rate-limiting Steps during the Human Mitochondrial Transcription Cycle in Vitro

May 01, 2010
Journal of Biological Chemistry
Maria F Lodeiro + 5 more +5

We have reconstituted human mitochondrial transcription in vitro on DNA oligonucleotide templates representing the light strand and heavy strand-1 promoters using protein components (RNA polymerase and transcription factors A and B2) isolated from Escherichia coli. We show that 1 eq of each transcription factor and polymerase relative to the promoter is required to assemble a functional initiation complex. The light strand promoter is at least 2-fold more efficient than the heavy strand-1 promoter, but this difference cannot be explained solely by the differences in the interaction of the transcription machinery with the different promoters. In both cases, the rate-limiting step for production of the first phosphodiester bond is open complex formation. Open complex formation requires both transcription factors; however, steps immediately thereafter only require transcription factor B2. The concentration of nucleotide required for production of the first dinucleotide product is substantially higher than that required for subsequent cycles of nucleotide addition. In vitro, promoter-specific differences in post-initiation control of transcription exist, as well as a second rate-limiting step that controls conversion of the transcription initiation complex into a transcription elongation complex. Rate-limiting steps of the biochemical pathways are often those that are targeted for regulation. Like the more complex multisubunit transcription systems, multiple steps may exist for control of transcription in human mitochondria. The tools and mechanistic framework presented here will facilitate not only the discovery of mechanisms regulating human mitochondrial transcription but also interrogation of the structure, function, and mechanism of the complexes that are regulated during human mitochondrial transcription.

Supplementary Content
141
10.1074/jbc.r700043200

Stem Cell Niche: Microenvironment and Beyond

Apr 01, 2008
Journal of Biological Chemistry
Jiwang Zhang + 1 more +1

The multipotentiality and self-renewal ability of stem cells are controlled by intrinsic genetic pathways that are subject to regulation by extrinsic signals emanating from the stem cell niche. The stem cell niche provides a microenvironment composed of cellular structures or extracellular matrix in which stem cells are maintained as undifferentiated (1Li L. Xie T. Annu. Rev. Cell Dev. Biol. 2005; 21: 605-631Crossref PubMed Scopus (942) Google Scholar, 2Lin H. Nat. Rev. Genet. 2002; 3: 931-940Crossref PubMed Scopus (305) Google Scholar, 3Scadden D.T. Nature. 2006; 441: 1075-1079Crossref PubMed Scopus (1508) Google Scholar, 4Spradling A. Drummond-Barbosa D. Kai T. Nature. 2001; 414: 98-104Crossref PubMed Scopus (1215) Google Scholar, 5Watt F.M. Hogan B.L. Science. 2000; 287: 1427-1430Crossref PubMed Scopus (1474) Google Scholar, 6Fuchs E. Tumbar T. Guasch G. Cell. 2004; 116: 769-778Abstract Full Text Full Text PDF PubMed Scopus (1481) Google Scholar). The concept of "the stem cell niche" was first proposed in studies of the HSC 2The abbreviations used are:HSChematopoietic stem cellGSCgerm line stem cellBMbone marrowCARCXCL12-abundant reticularCBscystoblastsESCescort stem cellCPscyst progenitorsAng-1angiopoietin-1.2The abbreviations used are:HSChematopoietic stem cellGSCgerm line stem cellBMbone marrowCARCXCL12-abundant reticularCBscystoblastsESCescort stem cellCPscyst progenitorsAng-1angiopoietin-1. (7Schofield R. Blood Cells. 1978; 4: 7-25PubMed Google Scholar); however, in vivo evidence of its existence was first shown in the Drosophila GSC (8Cox D.N. Chao A. Baker J. Chang L. Qiao D. Lin H. Genes Dev. 1998; 12: 3715-3727Crossref PubMed Scopus (802) Google Scholar, 9King F.J. Lin H. Development (Camb.). 1999; 126: 1833-1844PubMed Google Scholar, 10Xie T. Spradling A.C. Science. 2000; 290: 328-330Crossref PubMed Scopus (620) Google Scholar). Over the past several years, there has been much progress made in identifying stem cell niches in different mammal tissues, including nerves, hair follicles, intestines, teeth, and BM (11Tumbar T. Guasch G. Greco V. Blanpain C. Lowry W.E. Rendl M. Fuchs E. Science. 2004; 303: 359-363Crossref PubMed Scopus (1631) Google Scholar, 12Yen T.H. Wright N.A. Stem Cell Rev. 2006; 2: 203-212Crossref PubMed Scopus (227) Google Scholar, 13Conover J.C. Notti R.Q. Cell Tissue Res. 2008; 331: 211-224Crossref PubMed Scopus (123) Google Scholar, 14Doetsch F. Curr. Opin. Genet. Dev. 2003; 13: 543-550Crossref PubMed Scopus (529) Google Scholar, 15Ohshima H. Nakasone N. Hashimoto E. Sakai H. Nakakura-Ohshima K. Harada H. Arch. Oral Biol. 2005; 50: 153-157Crossref PubMed Scopus (81) Google Scholar, 16Wilson A. Trumpp A. Nat. Rev. Immunol. 2006; 6: 93-106Crossref PubMed Scopus (1050) Google Scholar). In this review, our focus is on comparing Drosophila GSC niches and mouse HSC niches (two of the best characterized niches). By such comparison, we hope to provide some common principles of stem cell niches that will be useful in other tissue stem cell niche studies. hematopoietic stem cell germ line stem cell bone marrow CXCL12-abundant reticular cystoblasts escort stem cell cyst progenitors angiopoietin-1. hematopoietic stem cell germ line stem cell bone marrow CXCL12-abundant reticular cystoblasts escort stem cell cyst progenitors angiopoietin-1. In recent years, remarkable progress has been made in the identification and characterization of the stem cell niches in invertebrate systems (10Xie T. Spradling A.C. Science. 2000; 290: 328-330Crossref PubMed Scopus (620) Google Scholar, 17Tulina N. Matunis E. Science. 2001; 294: 2546-2549Crossref PubMed Scopus (506) Google Scholar, 18Kiger A.A. Jones D.L. Schulz C. Rogers M.B. Fuller M.T. Science. 2001; 294: 2542-2545Crossref PubMed Scopus (538) Google Scholar, 19Lin H. Spradling A.C. Dev. Genet. 1995; 16: 6-12Crossref PubMed Scopus (180) Google Scholar, 20Crittenden S.L. Bernstein D.S. Bachorik J.L. Thompson B.E. Gallegos M. Petcherski A.G. Moulder G. Barstead R. Wickens M. Kimble J. Nature. 2002; 417: 660-663Crossref PubMed Scopus (337) Google Scholar, 21Mandal L. Martinez-Agosto J.A. Evans C.J. Hartenstein V. Banerjee U. Nature. 2007; 446: 320-324Crossref PubMed Scopus (220) Google Scholar, 22Krzemien J. Dubois L. Makki R. Meister M. Vincent A. Crozatier M. Nature. 2007; 446: 325-328Crossref PubMed Scopus (246) Google Scholar). In studies of GSCs in Drosophila, the ovary and testis provide relatively simple but elegant anatomic structures with few cell types and unique stem cell markers. These advantages facilitated identification of the cellular components of the stem cell niche and definition of the molecular basis of physical interaction between stem cells and their niches (23Song X. Xie T. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 14813-14818Crossref PubMed Scopus (184) Google Scholar, 24Yamashita Y.M. Jones D.L. Fuller M.T. Science. 2003; 301: 1547-1550Crossref PubMed Scopus (595) Google Scholar) and revealed key niche signals involved in stem cell regulation (18Kiger A.A. Jones D.L. Schulz C. Rogers M.B. Fuller M.T. Science. 2001; 294: 2542-2545Crossref PubMed Scopus (538) Google Scholar, 25LaFever L. Drummond-Barbosa D. Science. 2005; 309: 1071-1073Crossref PubMed Scopus (248) Google Scholar, 26Szakmary A. Cox D.N. Wang Z. Lin H. Curr. Biol. 2005; 15: 171-178Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar, 27Xie T. Spradling A.C. Cell. 1998; 94: 251-260Abstract Full Text Full Text PDF PubMed Scopus (530) Google Scholar, 28Yamashita Y.M. 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Two HSC niches have been proposed in murine BM, an osteoblastic niche and a vascular niche, in which osteoblasts and vascular endothelial cells have been demonstrated as major components, respectively (34Zhang J. Niu C. Ye L. Huang H. He X. Tong W.G. Ross J. Haug J. Johnson T. Feng J.Q. Harris S. Wiedemann L.M. Mishina Y. Li L. Nature. 2003; 425: 836-841Crossref PubMed Scopus (2385) Google Scholar, 35Calvi L.M. Adams G.B. Weibrecht K.W. Weber J.M. Olson D.P. Knight M.C. Martin R.P. Schipani E. Divieti P. Bringhurst F.R. Milner L.A. Kronenberg H.M. Scadden D.T. Nature. 2003; 425: 841-846Crossref PubMed Scopus (2799) Google Scholar, 36Arai F. Hirao A. Ohmura M. Sato H. Matsuoka S. Takubo K. Ito K. Koh G.Y. Suda T. Cell. 2004; 118: 149-161Abstract Full Text Full Text PDF PubMed Scopus (1540) Google Scholar, 37Nilsson S.K. Johnston H.M. Whitty G.A. Williams B. Webb R.J. Denhardt D.T. Bertoncello I. Bendall L.J. Simmons P.J. Haylock D.N. Blood. 2005; 106: 1232-1239Crossref PubMed Scopus (605) Google Scholar, 38Heissig B. Rafii S. Akiyama H. Ohki Y. Sato Y. Rafael T. Zhu Z. Hicklin D.J. Okumura K. Ogawa H. Werb Z. Hattori K. J. Exp. Med. 2005; 202: 739-750Crossref PubMed Scopus (195) Google Scholar, 39Moore K.A. Curr. Opin. Hematol. 2004; 11: 107-111Crossref PubMed Scopus (56) Google Scholar, 40Taichman R.S. Blood. 2005; 105: 2631-2639Crossref PubMed Scopus (469) Google Scholar, 41Kiel M.J. Yilmaz O.H. Iwashita T. Terhorst C. Morrison S.J. Cell. 2005; 121: 1109-1121Abstract Full Text Full Text PDF PubMed Scopus (2414) Google Scholar). A recent study suggested that a population of reticular cells named CAR cells, which express a high level of CXCL12 (also known as stromal cell-derived factor-1 or pre-B cell growth-stimulating factor), are in contact with HSCs in both osteoblastic and vascular niches (42Sugiyama T. Kohara H. Noda M. Nagasawa T. Immunity. 2006; 25: 977-988Abstract Full Text Full Text PDF PubMed Scopus (1693) Google Scholar). Drosophila ovary and testis provide attractive models for stem cell niche studies. In Drosophila ovary, cap cells, a specific type of somatic cell located at the tip of the germarium in the ovary, function as the niche for GSCs. An E-cadherin/β-catenin-formed cell-cell adhesion junction mediates the physical interaction between GSCs and their niche cells (23Song X. Xie T. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 14813-14818Crossref PubMed Scopus (184) Google Scholar, 46Song X. Zhu C.H. Doan C. Xie T. Science. 2002; 296: 1855-1857Crossref PubMed Scopus (389) Google Scholar), ensuring stem cell control by niche signals. Normally, asymmetric division of stem cells results in two daughter cells with different fates: one daughter cell attaches to the niche and is maintained as a stem cell (self-renewal), whereas the other daughter cell leaves the niche and develops into a cystoblast (1Li L. Xie T. Annu. Rev. Cell Dev. Biol. 2005; 21: 605-631Crossref PubMed Scopus (942) Google Scholar, 4Spradling A. Drummond-Barbosa D. Kai T. Nature. 2001; 414: 98-104Crossref PubMed Scopus (1215) Google Scholar). CBs undergo four incomplete cell divisions to form an interconnected 2–16-cell germ line cyst. In addition to the GSC, another type of cell called the ESC also attaches to cap cells interspersed between the GSCs. Together with cap cells, ESCs encapsulate GSCs to separate GSCs from their differentiated daughter cells. When the GSCs divide and detach from the niche to produce CBs and cyst cells, the ESCs also proliferate and differentiate to produce more escort cells. The escort cells expand and continue to encapsulate CBs and cysts during the process of cyst formation and are finally replaced by follicle cells after the 16-cell germ line cyst stage (Fig. 1a). Interestingly, the newly formed cysts (prior to the eight-cell cyst stage, while still encapsulated by the escort cell) can revert to the stem cell state under certain circumstances, suggesting that they may still retain (albeit limited) stem cell properties (47Kai T. Spradling A. Nature. 2004; 428: 564-569Crossref PubMed Scopus (267) Google Scholar). A similar niche is also found in Drosophila testis and is composed of hub cells located at the end of the testis (48Le Bras S. Van Doren M. Dev. Biol. 2006; 294: 92-103Crossref PubMed Scopus (96) Google Scholar). Male GSCs surrounding the hub cells are interspersed with CPs (which are counterparts of ESCs in the ovary). Both GSCs and CPs are attached to the hub cells through an adhesion junction. Similar to ESCs in the ovary, proliferation and differentiation of CPs always accompany proliferation and differentiation of GSCs. CPs in the testis produce cyst cells, which encapsulate the gonialblasts (the immediate daughters of male GSCs) during spermatogonium formation (Fig. 1b). The newly formed gonialblasts can also revert to stem cells under certain circumstances, resembling their counterpart cells (CBs and cysts) in the ovary (49Brawley C. Matunis E. Science. 2004; 304: 1331-1334Crossref PubMed Scopus (326) Google Scholar). The role of cap and hub cells in GSC regulation has been well studied, but the contribution of ESCs and their offspring in the ovary and CPs and their progeny in the testis to GSC self-renewal, proliferation, and differentiation is largely unknown. However, it is known that a dialogue between the two types of cells is required for the coordination during organogenesis (30King F.J. Szakmary A. Cox D.N. Lin H. Mol. Cell. 2001; 7: 497-508Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar). Cap and hub cells provide an attachment point for anchoring GSCs to the niche; they also produce signals that inhibit differentiation but promote self-renewal of stem cells (17Tulina N. Matunis E. Science. 2001; 294: 2546-2549Crossref PubMed Scopus (506) Google Scholar). The stem cell niches in mammals are very complicated because of the complexity of cellular components of mammalian tissues, even though the mechanism for niche regulation is conserved from invertebrate to vertebrate. In mammals, BM tissue is composed of more than eight different hematopoietic cell lineages supported by a network of mesenchymal stromal cells and vascular endothelial cells. The two HSC niches, osteoblastic (34Zhang J. Niu C. Ye L. Huang H. He X. Tong W.G. Ross J. Haug J. Johnson T. Feng J.Q. Harris S. Wiedemann L.M. Mishina Y. Li L. Nature. 2003; 425: 836-841Crossref PubMed Scopus (2385) Google Scholar, 35Calvi L.M. Adams G.B. Weibrecht K.W. Weber J.M. Olson D.P. Knight M.C. Martin R.P. Schipani E. Divieti P. Bringhurst F.R. Milner L.A. Kronenberg H.M. Scadden D.T. Nature. 2003; 425: 841-846Crossref PubMed Scopus (2799) Google Scholar, 36Arai F. Hirao A. Ohmura M. Sato H. Matsuoka S. Takubo K. Ito K. Koh G.Y. Suda T. Cell. 2004; 118: 149-161Abstract Full Text Full Text PDF PubMed Scopus (1540) Google Scholar, 37Nilsson S.K. Johnston H.M. Whitty G.A. Williams B. Webb R.J. Denhardt D.T. Bertoncello I. Bendall L.J. Simmons P.J. Haylock D.N. Blood. 2005; 106: 1232-1239Crossref PubMed Scopus (605) Google Scholar, 38Heissig B. Rafii S. Akiyama H. Ohki Y. Sato Y. Rafael T. Zhu Z. Hicklin D.J. Okumura K. Ogawa H. Werb Z. Hattori K. J. Exp. Med. 2005; 202: 739-750Crossref PubMed Scopus (195) Google Scholar, 39Moore K.A. Curr. Opin. Hematol. 2004; 11: 107-111Crossref PubMed Scopus (56) Google Scholar, 40Taichman R.S. Blood. 2005; 105: 2631-2639Crossref PubMed Scopus (469) Google Scholar, 41Kiel M.J. Yilmaz O.H. Iwashita T. Terhorst C. Morrison S.J. Cell. 2005; 121: 1109-1121Abstract Full Text Full Text PDF PubMed Scopus (2414) Google Scholar, 50Balduino A. Hurtado S.P. Frazao P. Takiya C.M. Alves L.M. Nasciutti L.E. El-Cheikh M.C. Borojevic R. Cell Tissue Res. 2005; 319: 255-266Crossref PubMed Scopus (90) Google Scholar, 51Arai F. Hirao A. Suda T. Trends Cardiovasc. Med. 2005; 15: 75-79Crossref PubMed Scopus (66) Google Scholar, 52Adams G.B. Chabner K.T. Alley I.R. Olson D.P. Szczepiorkowski Z.M. Poznansky M.C. Kos C.H. Pollak M.R. Brown E.M. Scadden D.T. Nature. 2006; 439: 599-603Crossref PubMed Scopus (600) Google Scholar) and vascular (41Kiel M.J. Yilmaz O.H. Iwashita T. Terhorst C. Morrison S.J. Cell. 2005; 121: 1109-1121Abstract Full Text Full Text PDF PubMed Scopus (2414) Google Scholar, 53Kopp H.G. Avecilla S.T. Hooper A.T. Rafii S. Physiology. 2005; 20: 349-356Crossref PubMed Scopus (414) Google Scholar), are found in adult BM tissue. The vascular niche might also exist in fetal hematopoietic tissues such as yolk sac, aorta-gonad-mesonephros region, placenta, liver, and spleen (54Tavian M. Peault B. Exp. Hematol. 2005; 33: 1062-1069Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, 55Basto D. Trovisco V. Lopes J.M. Martins A. Pardal F. Soares P. Reis R.M. Acta Neuropathol. 2005; 109: 207-210Crossref PubMed Scopus (84) Google Scholar, 56Gekas C. Dieterlen-Lièvre F. Orkin S.H. Millola H.K.A. Dev. Cell. 2005; 8: 365-375Abstract Full Text Full Text PDF PubMed Scopus (504) Google Scholar) as well as in adult spleen and liver. Both niches may be critical for HSC self-renewal. Cooperation between these two niches might be required for maintaining normal hematopoietic homeostasis and re-establishing hematopoiesis after injury. Accumulated evidence supports the existence of an osteoblastic niche in BM. 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