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Donato MG, Monaca MA, Faggio G, Stefano LD, Jones PH, Gucciardi PG, Maragò OM. Optical trapping of porous silicon nanoparticles. NANOTECHNOLOGY 2011; 22:505704. [PMID: 22108540 DOI: 10.1088/0957-4484/22/50/505704] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Silicon nanoparticles obtained by ball-milling of a 50% porosity silicon layer have been optically trapped when dispersed in a water-surfactant environment. We measured the optical force constants using linearly and radially polarized trapping beams finding a reshaping of the optical potential and an enhanced axial spring constant for the latter. These measurements open perspectives for the control and handling of silicon nanoparticles as labeling agents in biological analysis and fluorescence imaging techniques.
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Ridolfo A, Saija R, Savasta S, Jones PH, Iatì MA, Maragò OM. Fano-Doppler laser cooling of hybrid nanostructures. ACS NANO 2011; 5:7354-7361. [PMID: 21806014 DOI: 10.1021/nn2022364] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Laser cooling the center-of-mass motion of systems that exhibit Fano resonances is discussed. We find that cooling occurs for red or blue detuning of the laser frequency from resonance depending on the Fano factor associated with the resonance. The combination of the Doppler effect with the radiation cross-section quenching typical of quantum interference yields temperatures below the conventional Doppler limit. This scheme opens perspectives for controlling the motion of mesoscopic systems such as hybrid nanostructures at the quantum regime and the exploration of motional nonclassical states at the nanoscale.
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Radford AD, Noble PJ, Coyne KP, Gaskell RM, Jones PH, Bryan JGE, Setzkorn C, Tierney Á, Dawson S. Antibacterial prescribing patterns in small animal veterinary practice identified via SAVSNET: the small animal veterinary surveillance network. Vet Rec 2011; 169:310. [PMID: 21911433 DOI: 10.1136/vr.d5062] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
In this study, data from veterinary clinical records were collected via the small animal veterinary surveillance network (SAVSNET). Over a three-month period, data were obtained from 22,859 consultations at 16 small animal practices in England and Wales: 69 per cent from dogs, 24 per cent from cats, 3 per cent from rabbits and 4 per cent from miscellaneous species. The proportion of consults where prescribing of antibacterials was identified was 35.1 per cent for dogs, 48.5 per cent for cats and 36.6 per cent for rabbits. Within this population, 76 per cent of antibacterials prescribed were β-lactams, including the most common group of clavulanic acid-potentiated amoxicillin making up 36 per cent of the antibacterials prescribed. Other classes included lincosamides (9 per cent), fluoroquinolones and quinolones (6 per cent) and nitroimidazoles (4 per cent). Vancomycin and teicoplanin (glycopeptide class), and imipenem and meropenem (β-lactam class) prescribing was not identified. Prescribing behaviour varied between practices. For dogs and cats, the proportion of consults associated with the prescription of antibacterials ranged from 0.26 to 0.55 and 0.41 to 0.73, respectively.
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Jones PH, Washburn LR, Britten HB. Gene flow in a Yersinia pestis vector, Oropsylla hirsuta, during a plague epizootic. J Vector Borne Dis 2011; 48:125-132. [PMID: 21946710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023] Open
Abstract
BACKGROUND & OBJECTIVES Appreciating how Yersinia pestis, the etiological agent of plague, spreads among black - tailed prairie dog (Cynomys ludovicianus) colonies (BTPD), is vital to wildlife conservation programs in North American grasslands. A little - studied aspect of the system is the role of Y. pestis vectors, i.e. fleas, play in the spreading of plague in natural settings. We investigated the genetic structure and variability of a common prairie dog flea (Oropsylla hirsuta) in BTPD colonies in order to examine dispersal patterns. Given that this research took place during a widespread plague epizootic, there was the added advantage of gaining information on the dynamics of sylvatic plague. METHODS & RESULTS Oropsylla hirsuta were collected from BTPD burrows in nine colonies from May 2005 to July 2005, and eight polymorphic microsatellite markers were used to generate genotypic data from them. Gene flow estimates revealed low genetic differentiation among fleas sampled from different colonies. NestedPCR plague assays confirmed the presence of Y. pestis with the average Y. pestis prevalence across all nine colonies at 12%. No significant correlations were found between the genetic variability and gene flow of O. hirsuta and Y. pestis prevalence on a per -colony basis. CONCLUSION Oropsylla hirsuta dispersal among BTPD colonies was high, potentially explaining the rapid spread of Y. pestis in our study area in 2005 and 2006.
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Fowler JC, Zecchini VR, Jones PH. Intestinal activation of Notch signaling induces rapid onset hepatic steatosis and insulin resistance. PLoS One 2011; 6:e20767. [PMID: 21698231 PMCID: PMC3116826 DOI: 10.1371/journal.pone.0020767] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 05/09/2011] [Indexed: 02/07/2023] Open
Abstract
Here we investigate the effects of expressing an activated mutant of Notch (ICD-E) in an inducible transgenic mouse model. Hepatic expression of ICD-E in adult animals has no detectable phenotype, but simultaneous induction of ICD-E in both the liver and small intestine results in hepatic steatosis, lipogranuloma formation and mild insulin resistance within 96 hours. This supports work that suggests that fatty liver disease may result from disruption of the gut-liver axis. In the intestine, ICD-E expression is known to produce a transient change in the proportion of goblet cells followed by shedding of the recombinant epithelium. We report additional intestinal transcriptional changes following ICD-E expression, finding significant transcriptional down-regulation of rpL29 (ribosomal protein L29), which is implicated in the regulation of intestinal flora. These results provide further evidence of a gut-liver axis in the development of fatty liver disease and insulin resistance and validate a new model for future studies of hepatic steatosis.
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Klein AM, Nikolaidou-Neokosmidou V, Doupé DP, Jones PH, Simons BD. Patterning as a signature of human epidermal stem cell regulation. J R Soc Interface 2011; 8:1815-24. [PMID: 21632613 DOI: 10.1098/rsif.2011.0240] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Understanding how stem cells are regulated in adult tissues is a major challenge in cell biology. In the basal layer of human epidermis, clusters of almost quiescent stem cells are interspersed with proliferating and differentiating cells. Previous studies have shown that the proliferating cells follow a pattern of balanced stochastic cell fate. This behaviour enables them to maintain homeostasis, while stem cells remain confined to their quiescent clusters. Intriguingly, these clusters reappear spontaneously in culture, suggesting that they may play a functional role in stem cell auto-regulation. We propose a model of pattern formation that explains how clustering could regulate stem cell activity in homeostatic tissue through contact inhibition and stem cell aggregation.
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van der Weyden L, Alcolea MP, Jones PH, Rust AG, Arends MJ, Adams DJ. Acute sensitivity of the oral mucosa to oncogenic K-ras. J Pathol 2011; 224:22-32. [PMID: 21381032 PMCID: PMC3627303 DOI: 10.1002/path.2853] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 12/23/2010] [Accepted: 12/24/2010] [Indexed: 01/08/2023]
Abstract
Mouse models of cancer represent powerful tools for analysing the role of genetic alterations in carcinogenesis. Using a mouse model that allows tamoxifen-inducible somatic activation (by Cre-mediated recombination) of oncogenic K-rasG12D in a wide range of tissues, we observed hyperplasia of squamous epithelium located in moist or frequently abraded mucosa, with the most dramatic effects in the oral mucosa. This epithelium showed a sequence of squamous hyperplasia followed by squamous papilloma with dysplasia, in which some areas progressed to early invasive squamous cell carcinoma, within 14 days of widespread oncogenic K-ras activation. The marked proliferative response of the oral mucosa to K-rasG12D was most evident in the basal layers of the squamous epithelium of the outer lip with hair follicles and wet mucosal surface, with these cells staining positively for pAKT and cyclin D1, showing Ras/AKT pathway activation and increased proliferation with Ki-67 and EdU positivity. The stromal cells also showed gene activation by recombination and immunopositivity for pERK indicating K-Ras/ERK pathway activation, but without Ki-67 positivity or increase in stromal proliferation. The oral neoplasms showed changes in the expression pattern of cytokeratins (CK6 and CK13), similar to those observed in human oral tumours. Sporadic activation of the K-rasG12D allele (due to background spontaneous recombination in occasional cells) resulted in the development of benign oral squamous papillomas only showing a mild degree of dysplasia with no invasion. In summary, we show that oral mucosa is acutely sensitive to oncogenic K-ras, as widespread expression of activated K-ras in the murine oral mucosal squamous epithelium and underlying stroma can drive the oral squamous papilloma–carcinoma sequence. Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
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Maragó OM, Bonaccorso F, Saija R, Privitera G, Gucciardi PG, Iatì MA, Calogero G, Jones PH, Borghese F, Denti P, Nicolosi V, Ferrari AC. Brownian motion of graphene. ACS NANO 2010; 4:7515-7523. [PMID: 21133432 DOI: 10.1021/nn1018126] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Brownian motion is a manifestation of the fluctuation-dissipation theorem of statistical mechanics. It regulates systems in physics, biology, chemistry, and finance. We use graphene as prototype material to unravel the consequences of the fluctuation-dissipation theorem in two dimensions, by studying the Brownian motion of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics in the optical trap and measure force and torque constants from the correlation functions of the tracking signals, as well as comparing experiments with a full electromagnetic theory of optical trapping. The understanding of optical trapping of two-dimensional nanostructures gained through our Brownian motion analysis paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.
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Radford A, Tierney A, Coyne KP, Gaskell RM, Noble PJ, Dawson S, Setzkorn C, Jones PH, Buchan IE, Newton JR, Bryan JGE. Developing a network for small animal disease surveillance. Vet Rec 2010; 167:472-4. [PMID: 20871079 DOI: 10.1136/vr.c5180] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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Abstract
Quantitative lineage tracing reveals stem cell fate in vivo. A new study in a recent issue of Cell shows intestinal crypt stem cells are functionally equivalent, with equal odds of differentiation. Differentiating stem cells are replaced by the symmetric division of adjacent stem cells.
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Inman CF, Haverson K, Konstantinov SR, Jones PH, Harris C, Smidt H, Miller B, Bailey M, Stokes C. Rearing environment affects development of the immune system in neonates. Clin Exp Immunol 2010; 160:431-9. [PMID: 20184618 PMCID: PMC2883114 DOI: 10.1111/j.1365-2249.2010.04090.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Early-life exposure to appropriate microbial flora drives expansion and development of an efficient immune system. Aberrant development results in increased likelihood of allergic disease or increased susceptibility to infection. Thus, factors affecting microbial colonization may also affect the direction of immune responses in later life. There is a need for a manipulable animal model of environmental influences on the development of microbiota and the immune system during early life. We assessed the effects of rearing under low- (farm, sow) and high-hygiene (isolator, milk formula) conditions on intestinal microbiota and immune development in neonatal piglets, because they can be removed from the mother in the first 24 h for rearing under controlled conditions and, due to placental structure, neither antibody nor antigen is transferred in utero. Microbiota in both groups was similar between 2 and 5 days. However, by 12-28 days, piglets reared on the mother had more diverse flora than siblings reared in isolators. Dendritic cells accumulated in the intestinal mucosa in both groups, but more rapidly in isolator piglets. Importantly, the minority of 2-5-day-old farm piglets whose microbiota resembled that of an older (12-28-day-old) pig also accumulated dendritic cells earlier than the other farm-reared piglets. Consistent with dendritic cell control of T cell function, the effects on T cells occurred at later time-points, and mucosal T cells from high-hygiene, isolator pigs made less interleukin (IL)-4 while systemic T cells made more IL-2. Neonatal piglets may be a valuable model for studies of the effects of interaction between microbiota and immune development on allergy.
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White CI, Birtles RJ, Wigley P, Jones PH. Mycobacterium avium subspecies paratuberculosis in free-living amoebae isolated from fields not used for grazing. Vet Rec 2010; 166:401-2. [PMID: 20348470 DOI: 10.1136/vr.b4797] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Doupé DP, Klein AM, Simons BD, Jones PH. The ordered architecture of murine ear epidermis is maintained by progenitor cells with random fate. Dev Cell 2010; 18:317-23. [PMID: 20159601 DOI: 10.1016/j.devcel.2009.12.016] [Citation(s) in RCA: 179] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 11/27/2009] [Accepted: 12/16/2009] [Indexed: 12/31/2022]
Abstract
Typical murine epidermis has a patterned structure, seen clearly in ear skin, with regular columns of differentiated cells overlying the proliferative basal layer. It has been proposed that each column is a clonal epidermal proliferative unit maintained by a central stem cell and its transit amplifying cell progeny. An alternative hypothesis is that proliferating basal cells have random fate, the probability of generating cycling or differentiated cells being balanced so homeostasis is achieved. The stochastic model seems irreconcilable with an ordered tissue. Here we use lineage tracing to reveal that basal cells generate clones with highly irregular shapes that contribute progeny to multiple columns. Basal cell fate and cell cycle time is random. Cell columns form due to the properties of postmitotic cells. We conclude that the ordered architecture of the epidermis is maintained by a stochastic progenitor cell population, providing a simple and robust mechanism of homeostasis.
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Jones PH, Palmisano F, Bonaccorso F, Gucciardi PG, Calogero G, Ferrari AC, Maragó OM. Rotation detection in light-driven nanorotors. ACS NANO 2009; 3:3077-3084. [PMID: 19856981 DOI: 10.1021/nn900818n] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We analyze the rotational dynamics of light driven nanorotors, made of nanotube bundles and gold nanorods aggregates, with nonsymmetric shapes, trapped in optical tweezers. We identify two different regimes depending on dimensions and optical properties of the nanostructures. These correspond to alignment with either the laser propagation axis or the dominant polarization direction, or rotational motions caused by either unbalanced radiation pressure or polarization torque. By analyzing the motion correlations of the trapped nanostructures, we measure with high accuracy both the optical trapping parameters and the rotation frequency induced by the radiation pressure. Our results pave the way to improved all-optical detection, control over rotating nanomachines, and rotation detection in nano-optomechanics.
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Jones PH, Rashid M, Makita M, Maragò OM. Sagnac interferometer method for synthesis of fractional polarization vortices. OPTICS LETTERS 2009; 34:2560-2562. [PMID: 19724489 DOI: 10.1364/ol.34.002560] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We present a method for producing laser beams of nonuniform polarization where the polarization direction rotates on a trajectory about the beam propagation direction. Our method uses a Sagnac interferometer that incorporates a spatial light modulator to combine beams that possess oppositely charged phase vortices in order to achieve the desired polarization vortex. We demonstrate the utility of our method by producing polarization vortices characterized by a fractional index, and we compare the results with calculations of the expected fields.
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Haverson K, Corfield G, Jones PH, Kenny M, Fowler J, Bailey M, Stokes CR, Miller BG. Effect of oral antigen and antibody exposure at birth on subsequent immune status. A study in neonatal pigs. Int Arch Allergy Immunol 2009; 150:192-204. [PMID: 19439986 DOI: 10.1159/000218123] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 12/23/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The purpose of this work was to investigate the effects of early low-level exposure to either antigen or antibody alone on subsequent immune responses in entirely immunologically naïve animals. This is impossible in species with a permeable placenta such as rodents or humans, where both antigen and antibody can be transferred in utero. It is, however, possible in pigs, due to the impermeable placenta of the sow. Thus, neonatal piglets were used for this study. METHODS Newborn piglets were exposed to ovalbumin (OVA) at dosages similar to those used in rodents to sensitise, as well as to serum containing anti-OVA antibodies. RESULTS Both single low doses of OVA (10 and 1,000 mg per animal) induced classical oral tolerance following a systemic challenge: both doses reduced specific systemic IgG responses and tertiary in vitro recall proliferative responses by splenocytes and especially by mesenteric lymph node (MLN) cells. Additionally, dietary challenge had phenotypic effects on helper T cells in MLN, which could be reversed by OVA at birth. In contrast, giving antibody as serum collected from hyperimmune or orally tolerant pigs had no functional effects. CONCLUSIONS Overall, our data support the hypothesis that contrary to previous work in rodents, very early exposure of neonatal pigs to a single small dose of antigen can reduce subsequent immune responses. This may have implications for human health. However, although these data point to a reducing/regulatory effect of low doses of antigen in very young animals, they cannot be extrapolated directly to allergy.
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Maragò OM, Jones PH, Bonaccorso F, Scardaci V, Gucciardi PG, Rozhin AG, Ferrari AC. Femtonewton force sensing with optically trapped nanotubes. NANO LETTERS 2008; 8:3211-6. [PMID: 18767887 DOI: 10.1021/nl8015413] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We extract the distribution of both center-of-mass and angular fluctuations from three-dimensional tracking of optically trapped nanotubes. We measure the optical force and torque constants from autocorrelation and cross-correlation of the tracking signals. This allows us to isolate the angular Brownian motion. We demonstrate that nanotubes enable nanometer spatial and femtonewton force resolution in photonic force microscopy, the smallest to date. This has wide implications in nanotechnology, biotechnology, nanofluidics, and material science.
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Klein AM, Doupé DP, Jones PH, Simons BD. Mechanism of murine epidermal maintenance: cell division and the voter model. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:031907. [PMID: 18517422 DOI: 10.1103/physreve.77.031907] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2007] [Revised: 11/30/2007] [Indexed: 05/26/2023]
Abstract
The dynamics of a genetically labeled cell population may be used to infer the laws of cell division in mammalian tissue. Recently, we showed that in mouse tail skin, where proliferating cells are confined to a two-dimensional layer, cells proliferate and differentiate according to a simple stochastic model of cell division involving just one type of proliferating cell that may divide both symmetrically and asymmetrically. Curiously, these simple rules provide excellent predictions of the cell population dynamics without having to address the cells' spatial distribution. Yet, if the spatial behavior of cells is addressed by allowing cells to diffuse at random, one deduces that density fluctuations destroy tissue confluence, implying some hidden degree of spatial regulation of cell division. To infer the mechanism of spatial regulation, we consider a two-dimensional model of cell fate that preserves the overall population dynamics. By identifying the resulting behavior with a three-species variation of the voter model, we predict that proliferating cells in the basal layer should cluster. Analysis of empirical correlations of cells stained for proliferation activity confirms that the expected clustering behavior is indeed seen in nature. As well as explaining how cells maintain a uniform two-dimensional density, these findings present an interesting experimental example of voter-model statistics in biology.
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Albertella MR, Loadman PM, Jones PH, Phillips RM, Rampling R, Burnet N, Alcock C, Anthoney A, Vjaters E, Dunk CR, Harris PA, Wong A, Lalani AS, Twelves CJ. Hypoxia-Selective Targeting by the Bioreductive Prodrug AQ4N in Patients with Solid Tumors: Results of a Phase I Study. Clin Cancer Res 2008; 14:1096-104. [PMID: 18281542 DOI: 10.1158/1078-0432.ccr-07-4020] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Jones PH, Simons BD, Watt FM. Sic Transit Gloria: Farewell to the Epidermal Transit Amplifying Cell? Cell Stem Cell 2007; 1:371-81. [DOI: 10.1016/j.stem.2007.09.014] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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122
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Jones PH, Maragó OM, Stride EPJ. Parametrization of trapping forces on microbubbles in scanning optical tweezers. ACTA ACUST UNITED AC 2007. [DOI: 10.1088/1464-4258/9/8/s23] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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123
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Clayton E, Doupé DP, Klein AM, Winton DJ, Simons BD, Jones PH. A single type of progenitor cell maintains normal epidermis. Nature 2007; 446:185-9. [PMID: 17330052 DOI: 10.1038/nature05574] [Citation(s) in RCA: 618] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Accepted: 11/24/2006] [Indexed: 11/09/2022]
Abstract
According to the current model of adult epidermal homeostasis, skin tissue is maintained by two discrete populations of progenitor cells: self-renewing stem cells; and their progeny, known as transit amplifying cells, which differentiate after several rounds of cell division. By making use of inducible genetic labelling, we have tracked the fate of a representative sample of progenitor cells in mouse tail epidermis at single-cell resolution in vivo at time intervals up to one year. Here we show that clone-size distributions are consistent with a new model of homeostasis involving only one type of progenitor cell. These cells are found to undergo both symmetric and asymmetric division at rates that ensure epidermal homeostasis. The results raise important questions about the potential role of stem cells on tissue maintenance in vivo.
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Jones PH, Goonasekera M, Meacher DR, Jonckheere T, Monteiro TS. Directed motion for delta-kicked atoms with broken symmetries: comparison between theory and experiment. PHYSICAL REVIEW LETTERS 2007; 98:073002. [PMID: 17359021 DOI: 10.1103/physrevlett.98.073002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2006] [Indexed: 05/14/2023]
Abstract
We report an experimental investigation of momentum diffusion in the delta-function kicked rotor where time symmetry is broken by a two-period kicking cycle and spatial symmetry by an alternating linear potential. We exploit this, and a technique involving a moving optical potential, to create an asymmetry in the momentum diffusion that is due to the classical chaotic diffusion. This represents a realization of a type of Hamiltonian quantum ratchet.
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Parratt CA, Chapman KJ, Turner C, Jones PH, Mendl MT, Miller BG. The fighting behaviour of piglets mixed before and after weaning in the presence or absence of a sow. Appl Anim Behav Sci 2006. [DOI: 10.1016/j.applanim.2006.01.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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