1
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Buescher FM, Schmitz MT, Frett T, Kramme J, de Boni L, Elmenhorst EM, Mulder E, Moestl S, Heusser K, Frings-Meuthen P, Jordan J, Rittweger J, Pesta D. Effects of 30 days bed rest and exercise countermeasures on PBMC bioenergetics. Acta Physiol (Oxf) 2024; 240:e14102. [PMID: 38294173 DOI: 10.1111/apha.14102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Revised: 12/27/2023] [Accepted: 01/08/2024] [Indexed: 02/01/2024]
Abstract
AIM Altered mitochondrial function across various tissues is a key determinant of spaceflight-induced physical deconditioning. In comparison to tissue biopsies, blood cell bioenergetics holds promise as a systemic and more readily accessible biomarker, which was evaluated during head-down tilt bed rest (HDTBR), an established ground-based analog for spaceflight-induced physiological changes in humans. More specifically, this study explored the effects of HDTBR and an exercise countermeasure on mitochondrial respiration in peripheral blood mononuclear cells (PBMCs). METHODS We subjected 24 healthy participants to a strict 30-day HDTBR protocol. The control group (n = 12) underwent HDTBR only, while the countermeasure group (n = 12) engaged in regular supine cycling exercise followed by veno-occlusive thigh cuffs post-exercise for 6 h. We assessed routine blood parameters 14 days before bed rest, the respiratory capacity of PBMCs via high-resolution respirometry, and citrate synthase activity 2 days before and at day 30 of bed rest. We confirmed PBMC composition by flow cytometry. RESULTS The change of the PBMC maximal oxidative phosphorylation capacity (OXPHOS) amounted to an 11% increase in the countermeasure group, while it decreased by 10% in the control group (p = 0.04). The limitation of OXPHOS increased in control only while other respiratory states were not affected by either intervention. Correlation analysis revealed positive associations between white blood cells, lymphocytes, and basophils with PBMC bioenergetics in both groups. CONCLUSION This study reveals that a regular exercise countermeasure has a positive impact on PBMC mitochondrial function, confirming the potential application of blood cell bioenergetics for human spaceflight.
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Affiliation(s)
- F-M Buescher
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - M T Schmitz
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
- Institute of Medical Biometry, Informatics and Epidemiology, Medical Faculty, University of Bonn, Bonn, Germany
| | - T Frett
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - J Kramme
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
- Center for Endocrinology, Diabetes and Preventive Medicine (CEDP), University Hospital Cologne, Cologne, Germany
| | - L de Boni
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - E M Elmenhorst
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - E Mulder
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - S Moestl
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - K Heusser
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - P Frings-Meuthen
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - J Jordan
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
- Medical Faculty, University of Cologne, Cologne, Germany
| | - J Rittweger
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - D Pesta
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
- Center for Endocrinology, Diabetes and Preventive Medicine (CEDP), University Hospital Cologne, Cologne, Germany
- Medical Faculty, University of Cologne, Cologne, Germany
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany
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2
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Schmitz MT, Sandoval K, Chen CP, Mostajo-Radji MA, Seeley WW, Nowakowski TJ, Ye CJ, Paredes MF, Pollen AA. The development and evolution of inhibitory neurons in primate cerebrum. Nature 2022; 603:871-877. [PMID: 35322231 PMCID: PMC8967711 DOI: 10.1038/s41586-022-04510-w] [Citation(s) in RCA: 40] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 02/01/2022] [Indexed: 12/14/2022]
Abstract
Neuroanatomists have long speculated that expanded primate brains contain an increased morphological diversity of inhibitory neurons (INs)1, and recent studies have identified primate-specific neuronal populations at the molecular level2. However, we know little about the developmental mechanisms that specify evolutionarily novel cell types in the brain. Here, we reconstruct gene expression trajectories specifying INs generated throughout the neurogenic period in macaques and mice by analysing the transcriptomes of 250,181 cells. We find that the initial classes of INs generated prenatally are largely conserved among mammals. Nonetheless, we identify two contrasting developmental mechanisms for specifying evolutionarily novel cell types during prenatal development. First, we show that recently identified primate-specific TAC3 striatal INs are specified by a unique transcriptional programme in progenitors followed by induction of a distinct suite of neuropeptides and neurotransmitter receptors in new-born neurons. Second, we find that multiple classes of transcriptionally conserved olfactory bulb (OB)-bound precursors are redirected to expanded primate white matter and striatum. These classes include a novel peristriatal class of striatum laureatum neurons that resemble dopaminergic periglomerular cells of the OB. We propose an evolutionary model in which conserved initial classes of neurons supplying the smaller primate OB are reused in the enlarged striatum and cortex. Together, our results provide a unified developmental taxonomy of initial classes of mammalian INs and reveal multiple developmental mechanisms for neural cell type evolution. Evolutionary modelling shows that an initial set of inhibitory neurons serving olfactory bulbs may have been repurposed to diversify the taxonomy of interneurons found in the expanded striata and cortices in primates.
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Affiliation(s)
- Matthew T Schmitz
- Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, University of California, San Francisco, San Francisco, CA, USA.,Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Kadellyn Sandoval
- Department of Neurology, University of California, San Francisco, San Francisco, CA, USA.,Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA
| | - Christopher P Chen
- Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, University of California, San Francisco, San Francisco, CA, USA.,Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Mohammed A Mostajo-Radji
- Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, University of California, San Francisco, San Francisco, CA, USA.,Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - William W Seeley
- Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Tomasz J Nowakowski
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA.,Department of Anatomy, University of California, San Francisco, San Francisco, CA, USA.,Department of Psychiatry and Behavioral Sciences, University of California, San Francisco, San Francisco, CA, USA.,Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA, USA.,Chan Zuckerberg Biohub, San Francisco, CA, USA
| | - Chun Jimmie Ye
- Chan Zuckerberg Biohub, San Francisco, CA, USA.,Institute for Human Genetics, University of California, San Francisco, San Francisco, CA, USA.,Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, CA, USA.,Parker Institute for Cancer Immunotherapy, San Francisco, CA, USA
| | - Mercedes F Paredes
- Department of Neurology, University of California, San Francisco, San Francisco, CA, USA.,Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA
| | - Alex A Pollen
- Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, University of California, San Francisco, San Francisco, CA, USA. .,Department of Neurology, University of California, San Francisco, San Francisco, CA, USA. .,Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA. .,Chan Zuckerberg Biohub, San Francisco, CA, USA.
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3
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Brown J, Barry C, Schmitz MT, Argus C, Bolin JM, Schwartz MP, Van Aartsen A, Steill J, Swanson S, Stewart R, Thomson JA, Kendziorski C. Interspecies chimeric conditions affect the developmental rate of human pluripotent stem cells. PLoS Comput Biol 2021; 17:e1008778. [PMID: 33647016 PMCID: PMC7951976 DOI: 10.1371/journal.pcbi.1008778] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 03/11/2021] [Accepted: 02/08/2021] [Indexed: 12/17/2022] Open
Abstract
Human pluripotent stem cells hold significant promise for regenerative medicine. However, long differentiation protocols and immature characteristics of stem cell-derived cell types remain challenges to the development of many therapeutic applications. In contrast to the slow differentiation of human stem cells in vitro that mirrors a nine-month gestation period, mouse stem cells develop according to a much faster three-week gestation timeline. Here, we tested if co-differentiation with mouse pluripotent stem cells could accelerate the differentiation speed of human embryonic stem cells. Following a six-week RNA-sequencing time course of neural differentiation, we identified 929 human genes that were upregulated earlier and 535 genes that exhibited earlier peaked expression profiles in chimeric cell cultures than in human cell cultures alone. Genes with accelerated upregulation were significantly enriched in Gene Ontology terms associated with neurogenesis, neuron differentiation and maturation, and synapse signaling. Moreover, chimeric mixed samples correlated with in utero human embryonic samples earlier than human cells alone, and acceleration was dose-dependent on human-mouse co-culture ratios. The altered gene expression patterns and developmental rates described in this report have implications for accelerating human stem cell differentiation and the use of interspecies chimeric embryos in developing human organs for transplantation.
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Affiliation(s)
- Jared Brown
- Department of Statistics, University of Wisconsin-Madison, Wisconsin, United States of America
- * E-mail: (JB); (CK)
| | - Christopher Barry
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Matthew T. Schmitz
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Cara Argus
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Jennifer M. Bolin
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Michael P. Schwartz
- NSF Center for Sustainable Nanotechnology, Department of Chemistry, University of Wisconsin-Madison, Wisconsin, United States of America
| | - Amy Van Aartsen
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - John Steill
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Scott Swanson
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - Ron Stewart
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
| | - James A. Thomson
- Morgridge Institute for Research, Madison, Wisconsin, United States of America
- Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California, United States of America
| | - Christina Kendziorski
- Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison, Wisconsin, United States of America
- * E-mail: (JB); (CK)
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Mostajo-Radji MA, Schmitz MT, Montoya ST, Pollen AA. Reverse engineering human brain evolution using organoid models. Brain Res 2020; 1729:146582. [PMID: 31809699 PMCID: PMC7058376 DOI: 10.1016/j.brainres.2019.146582] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 11/25/2019] [Accepted: 11/29/2019] [Indexed: 02/06/2023]
Abstract
Primate brains vary dramatically in size and organization, but the genetic and developmental basis for these differences has been difficult to study due to lack of experimental models. Pluripotent stem cells and brain organoids provide a potential opportunity for comparative and functional studies of evolutionary differences, particularly during the early stages of neurogenesis. However, many challenges remain, including isolating stem cell lines from additional great ape individuals and species to capture the breadth of ape genetic diversity, improving the reproducibility of organoid models to study evolved differences in cell composition and combining multiple brain regions to capture connectivity relationships. Here, we describe strategies for identifying evolved developmental differences between humans and non-human primates and for isolating the underlying cellular and genetic mechanisms using comparative analyses, chimeric organoid culture, and genome engineering. In particular, we focus on how organoid models could ultimately be applied beyond studies of progenitor cell evolution to decode the origin of recent changes in cellular organization, connectivity patterns, myelination, synaptic development, and physiology that have been implicated in human cognition.
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Affiliation(s)
- Mohammed A Mostajo-Radji
- Department of Neurology, University of California San Francisco, San Francisco, CA 94143, USA; The Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California San Francisco, San Francisco, CA 94143, USA
| | - Matthew T Schmitz
- Department of Neurology, University of California San Francisco, San Francisco, CA 94143, USA; The Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California San Francisco, San Francisco, CA 94143, USA
| | - Sebastian Torres Montoya
- Health Co-creation Laboratory, Medellin General Hospital, Medellin, Antioquia, Colombia; Baskin School of Engineering, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Alex A Pollen
- Department of Neurology, University of California San Francisco, San Francisco, CA 94143, USA; The Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California San Francisco, San Francisco, CA 94143, USA.
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5
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Barry C, Schmitz MT, Argus C, Bolin JM, Probasco MD, Leng N, Duffin BM, Steill J, Swanson S, McIntosh BE, Stewart R, Kendziorski C, Thomson JA, Bacher R. Automated minute scale RNA-seq of pluripotent stem cell differentiation reveals early divergence of human and mouse gene expression kinetics. PLoS Comput Biol 2019; 15:e1007543. [PMID: 31815944 PMCID: PMC6922475 DOI: 10.1371/journal.pcbi.1007543] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 12/19/2019] [Accepted: 11/12/2019] [Indexed: 12/22/2022] Open
Abstract
Pluripotent stem cells retain the developmental timing of their species of origin in vitro, an observation that suggests the existence of a cell-intrinsic developmental clock, yet the nature and machinery of the clock remain a mystery. We hypothesize that one possible component may lie in species-specific differences in the kinetics of transcriptional responses to differentiation signals. Using a liquid-handling robot, mouse and human pluripotent stem cells were exposed to identical neural differentiation conditions and sampled for RNA-sequencing at high frequency, every 4 or 10 minutes, for the first 10 hours of differentiation to test for differences in transcriptomic response rates. The majority of initial transcriptional responses occurred within a rapid window in the first minutes of differentiation for both human and mouse stem cells. Despite similarly early onsets of gene expression changes, we observed shortened and condensed gene expression patterns in mouse pluripotent stem cells compared to protracted trends in human pluripotent stem cells. Moreover, the speed at which individual genes were upregulated, as measured by the slopes of gene expression changes over time, was significantly faster in mouse compared to human cells. These results suggest that downstream transcriptomic response kinetics to signaling cues are faster in mouse versus human cells, and may offer a partial account for the vast differences in developmental rates across species.
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Affiliation(s)
- Christopher Barry
- Morgridge Institute for Research, Madison, WI, United States of America
| | | | - Cara Argus
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Jennifer M. Bolin
- Morgridge Institute for Research, Madison, WI, United States of America
| | | | - Ning Leng
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Bret M. Duffin
- Morgridge Institute for Research, Madison, WI, United States of America
| | - John Steill
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Scott Swanson
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Brian E. McIntosh
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Ron Stewart
- Morgridge Institute for Research, Madison, WI, United States of America
| | - Christina Kendziorski
- Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison, Madison, WI, United States of America
| | - James A. Thomson
- Morgridge Institute for Research, Madison, WI, United States of America
- Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States of America
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA, United States of America
| | - Rhonda Bacher
- Department of Biostatistics, University of Florida, Gainesville, FL, United States of America
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6
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Barry C, Schmitz MT, Propson NE, Hou Z, Zhang J, Nguyen BK, Bolin JM, Jiang P, McIntosh BE, Probasco MD, Swanson S, Stewart R, Thomson JA, Schwartz MP, Murphy WL. Uniform neural tissue models produced on synthetic hydrogels using standard culture techniques. Exp Biol Med (Maywood) 2017; 242:1679-1689. [PMID: 28599598 PMCID: PMC5786368 DOI: 10.1177/1535370217715028] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The aim of the present study was to test sample reproducibility for model neural tissues formed on synthetic hydrogels. Human embryonic stem (ES) cell-derived precursor cells were cultured on synthetic poly(ethylene glycol) (PEG) hydrogels to promote differentiation and self-organization into model neural tissue constructs. Neural progenitor, vascular, and microglial precursor cells were combined on PEG hydrogels to mimic developmental timing, which produced multicomponent neural constructs with 3D neuronal and glial organization, organized vascular networks, and microglia with ramified morphologies. Spearman's rank correlation analysis of global gene expression profiles and a comparison of coefficient of variation for expressed genes demonstrated that replicate neural constructs were highly uniform to at least day 21 for samples from independent experiments. We also demonstrate that model neural tissues formed on PEG hydrogels using a simplified neural differentiation protocol correlated more strongly to in vivo brain development than samples cultured on tissue culture polystyrene surfaces alone. These results provide a proof-of-concept demonstration that 3D cellular models that mimic aspects of human brain development can be produced from human pluripotent stem cells with high sample uniformity between experiments by using standard culture techniques, cryopreserved cell stocks, and a synthetic extracellular matrix. Impact statement Pluripotent stem (PS) cells have been characterized by an inherent ability to self-organize into 3D "organoids" resembling stomach, intestine, liver, kidney, and brain tissues, offering a potentially powerful tool for modeling human development and disease. However, organoid formation must be quantitatively reproducible for applications such as drug and toxicity screening. Here, we report a strategy to produce uniform neural tissue constructs with reproducible global gene expression profiles for replicate samples from multiple experiments.
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Affiliation(s)
| | | | | | - Zhonggang Hou
- Morgridge Institute for Research, Madison, WI 53705, USA
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109, USA (current address)
| | - Jue Zhang
- Morgridge Institute for Research, Madison, WI 53705, USA
| | - Bao K Nguyen
- Morgridge Institute for Research, Madison, WI 53705, USA
| | | | - Peng Jiang
- Morgridge Institute for Research, Madison, WI 53705, USA
| | | | | | - Scott Swanson
- Morgridge Institute for Research, Madison, WI 53705, USA
| | - Ron Stewart
- Morgridge Institute for Research, Madison, WI 53705, USA
| | - James A Thomson
- Morgridge Institute for Research, Madison, WI 53705, USA
- Department of Cell & Regenerative Biology, University of Wisconsin-Madison, Madison, WI 53705, USA
- Department of Molecular, Cellular, & Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Michael P Schwartz
- Center for Sustainable Nanotechnology, Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - William L Murphy
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705, USA
- Materials Science Program, University of Wisconsin-Madison, WI 53705, USA
- Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI 53705, USA
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7
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Barry C, Schmitz MT, Jiang P, Schwartz MP, Duffin BM, Swanson S, Bacher R, Bolin JM, Elwell AL, McIntosh BE, Stewart R, Thomson JA. Species-specific developmental timing is maintained by pluripotent stem cells ex utero. Dev Biol 2017; 423:101-110. [PMID: 28179190 DOI: 10.1016/j.ydbio.2017.02.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 01/27/2017] [Accepted: 02/04/2017] [Indexed: 12/24/2022]
Abstract
How species-specific developmental timing is controlled is largely unknown. By following human embryonic stem (ES) cell and mouse epiblast stem (EpiS) cell differentiation through detailed RNA-sequencing time courses, here we show that pluripotent stem cells closely retain in vivo species-specific developmental timing in vitro. In identical neural differentiation conditions in vitro, gene expression profiles are accelerated in mouse EpiS cells compared to human ES cells with relative rates of differentiation closely reflecting the rates of progression through the Carnegie stages in utero. Dynamic Time Warping analysis identified 3389 genes that were regulated more quickly in mouse EpiS cells and identified none that were regulated more quickly in human ES cells. Interestingly, we also find that human ES cells differentiated in teratomas maintain the same rate of differentiation observed in vitro in spite of being grown in a mouse host. These results suggest the existence of a cell autonomous, species-specific developmental clock that pluripotent stem cells maintain even out of context of an intact embryo.
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Affiliation(s)
| | | | - Peng Jiang
- Morgridge Institute for Research, Madison, WI 53715, USA
| | - Michael P Schwartz
- Center for Sustainable Nanotechnology, Department of Chemistry, University of Wisconsin-Madison, WI 53706, USA
| | - Bret M Duffin
- Morgridge Institute for Research, Madison, WI 53715, USA
| | - Scott Swanson
- Morgridge Institute for Research, Madison, WI 53715, USA
| | - Rhonda Bacher
- Department of Statistics, University of Wisconsin-Madison, WI 53706, USA
| | | | | | | | - Ron Stewart
- Morgridge Institute for Research, Madison, WI 53715, USA
| | - James A Thomson
- Morgridge Institute for Research, Madison, WI 53715, USA; Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA; Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA.
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