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Zhang L, Cervantes MD, Pan S, Lindsley J, Dabney A, Kapler GM. Transcriptome analysis of the binucleate ciliate Tetrahymena thermophila with asynchronous nuclear cell cycles. Mol Biol Cell 2023; 34:rs1. [PMID: 36475712 PMCID: PMC9930529 DOI: 10.1091/mbc.e22-08-0326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Tetrahymena thermophila harbors two functionally and physically distinct nuclei within a shared cytoplasm. During vegetative growth, the "cell cycles" of the diploid micronucleus and polyploid macronucleus are offset. Micronuclear S phase initiates just before cytokinesis and is completed in daughter cells before onset of macronuclear DNA replication. Mitotic micronuclear division occurs mid-cell cycle, while macronuclear amitosis is coupled to cell division. Here we report the first RNA-seq cell cycle analysis of a binucleated ciliated protozoan. RNA was isolated across 1.5 vegetative cell cycles, starting with a macronuclear G1 population synchronized by centrifugal elutriation. Using MetaCycle, 3244 of the 26,000+ predicted genes were shown to be cell cycle regulated. Proteins present in both nuclei exhibit a single mRNA peak that always precedes their macronuclear function. Nucleus-limited genes, including nucleoporins and importins, are expressed before their respective nucleus-specific role. Cyclin D and A/B gene family members exhibit different expression patterns that suggest nucleus-restricted roles. Periodically expressed genes cluster into seven cyclic patterns. Four clusters have known PANTHER gene ontology terms associated with G1/S and G2/M phase. We propose that these clusters encode known and novel factors that coordinate micro- and macronuclear-specific events such as mitosis, amitosis, DNA replication, and cell division.
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Affiliation(s)
- L. Zhang
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,Department of Statistics, Texas A&M University, College Station, TX 77843
| | - M. D. Cervantes
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840
| | - S. Pan
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,Department of Statistics, Texas A&M University, College Station, TX 77843
| | - J. Lindsley
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840
| | - A. Dabney
- Department of Statistics, Texas A&M University, College Station, TX 77843,*Address correspondence to: Geoffrey Kapler (); A. Dabney ()
| | - G. M. Kapler
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,*Address correspondence to: Geoffrey Kapler (); A. Dabney ()
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2
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Lee SR, Pollard DA, Galati DF, Kelly ML, Miller B, Mong C, Morris MN, Roberts-Nygren K, Kapler GM, Zinkgraf M, Dang HQ, Branham E, Sasser J, Tessier E, Yoshiyama C, Matsumoto M, Turman G. Disruption of a ∼23-24 nucleotide small RNA pathway elevates DNA damage responses in Tetrahymena thermophila. Mol Biol Cell 2021; 32:1335-1346. [PMID: 34010017 PMCID: PMC8694037 DOI: 10.1091/mbc.e20-10-0631] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Endogenous RNA interference (RNAi) pathways regulate a wide range of cellular processes in diverse eukaryotes, yet in the ciliated eukaryote, Tetrahymena thermophila, the cellular purpose of RNAi pathways that generate ∼23–24 nucleotide (nt) small (s)RNAs has remained unknown. Here, we investigated the phenotypic and gene expression impacts on vegetatively growing cells when genes involved in ∼23–24 nt sRNA biogenesis are disrupted. We observed slower proliferation and increased expression of genes involved in DNA metabolism and chromosome organization and maintenance in sRNA biogenesis mutants RSP1Δ, RDN2Δ, and RDF2Δ. In addition, RSP1Δ and RDN2Δ cells frequently exhibited enlarged chromatin extrusion bodies, which are nonnuclear, DNA-containing structures that may be akin to mammalian micronuclei. Expression of homologous recombination factor Rad51 was specifically elevated in RSP1Δ and RDN2Δ strains, with Rad51 and double-stranded DNA break marker γ-H2A.X localized to discrete macronuclear foci. In addition, an increase in Rad51 and γ-H2A.X foci was also found in knockouts of TWI8, a macronucleus-localized PIWI protein. Together, our findings suggest that an evolutionarily conserved role for RNAi pathways in maintaining genome integrity may be extended even to the early branching eukaryotic lineage that gave rise to Tetrahymena thermophila.
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Affiliation(s)
- Suzanne R Lee
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Daniel A Pollard
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Domenico F Galati
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Megan L Kelly
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Brian Miller
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Christina Mong
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Megan N Morris
- Biology Department, Western Washington University, Bellingham, WA 98225
| | | | - Geoffrey M Kapler
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Matthew Zinkgraf
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Hung Q Dang
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Erica Branham
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Jason Sasser
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Erin Tessier
- Biology Department, Western Washington University, Bellingham, WA 98225
| | | | - Maya Matsumoto
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Gaea Turman
- Biology Department, Western Washington University, Bellingham, WA 98225
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3
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Gershman SJ, Balbi PE, Gallistel CR, Gunawardena J. Reconsidering the evidence for learning in single cells. eLife 2021; 10:61907. [PMID: 33395388 PMCID: PMC7781593 DOI: 10.7554/elife.61907] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 12/11/2020] [Indexed: 12/19/2022] Open
Abstract
The question of whether single cells can learn led to much debate in the early 20th century. The view prevailed that they were capable of non-associative learning but not of associative learning, such as Pavlovian conditioning. Experiments indicating the contrary were considered either non-reproducible or subject to more acceptable interpretations. Recent developments suggest that the time is right to reconsider this consensus. We exhume the experiments of Beatrice Gelber on Pavlovian conditioning in the ciliate Paramecium aurelia, and suggest that criticisms of her findings can now be reinterpreted. Gelber was a remarkable scientist whose absence from the historical record testifies to the prevailing orthodoxy that single cells cannot learn. Her work, and more recent studies, suggest that such learning may be evolutionarily more widespread and fundamental to life than previously thought and we discuss the implications for different aspects of biology.
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Affiliation(s)
- Samuel J Gershman
- Department of Psychology and Center for Brain Science, Harvard University, Cambridge, United States.,Center for Brains, Mind and Machines, MIT, Cambridge, United States
| | - Petra Em Balbi
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - C Randy Gallistel
- Rutgers Center for Cognitive Science, Rutgers University at New Brunswick, New Brunswick, United States
| | - Jeremy Gunawardena
- Department of Systems Biology, Harvard Medical School, Boston, United States
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Wahab S, Saettone A, Nabeel-Shah S, Dannah N, Fillingham J. Exploring the Histone Acetylation Cycle in the Protozoan Model Tetrahymena thermophila. Front Cell Dev Biol 2020; 8:509. [PMID: 32695779 PMCID: PMC7339932 DOI: 10.3389/fcell.2020.00509] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 05/28/2020] [Indexed: 12/22/2022] Open
Abstract
The eukaryotic histone acetylation cycle is composed of three classes of proteins, histone acetyltransferases (HATs) that add acetyl groups to lysine amino acids, bromodomain (BRD) containing proteins that are one of the most characterized of several protein domains that recognize acetyl-lysine (Kac) and effect downstream function, and histone deacetylases (HDACs) that catalyze the reverse reaction. Dysfunction of selected proteins of these three classes is associated with human disease such as cancer. Additionally, the HATs, BRDs, and HDACs of fungi and parasitic protozoa present potential drug targets. Despite their importance, the function and mechanisms of HATs, BRDs, and HDACs and how they relate to chromatin remodeling (CR) remain incompletely understood. Tetrahymena thermophila (Tt) provides a highly tractable single-celled free-living protozoan model for studying histone acetylation, featuring a massively acetylated somatic genome, a property that was exploited in the identification of the first nuclear/type A HAT Gcn5 in the 1990s. Since then, Tetrahymena remains an under-explored model for the molecular analysis of HATs, BRDs, and HDACs. Studies of HATs, BRDs, and HDACs in Tetrahymena have the potential to reveal the function of HATs and BRDs relevant to both fundamental eukaryotic biology and to the study of disease mechanisms in parasitic protozoa.
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Affiliation(s)
| | | | | | | | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
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Garg J, Saettone A, Nabeel-Shah S, Cadorin M, Ponce M, Marquez S, Pu S, Greenblatt J, Lambert JP, Pearlman RE, Fillingham J. The Med31 Conserved Component of the Divergent Mediator Complex in Tetrahymena thermophila Participates in Developmental Regulation. Curr Biol 2019; 29:2371-2379.e6. [PMID: 31280994 DOI: 10.1016/j.cub.2019.06.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 05/18/2019] [Accepted: 06/18/2019] [Indexed: 11/24/2022]
Abstract
Mediator is a large protein complex required for basal and regulated expression of most RNA polymerase II (RNAP II)-transcribed genes, in part due to its interaction with and phosphorylation of the conserved C-terminal domain (CTD) of Rpb1 [1, 2]. Mediator has been implicated in many aspects of gene expression including chromatin looping [3], higher-order chromatin folding [4], mRNA processing [5] and export [6], and transcriptional memory [7]. Mediator is thought to have played a major role during eukaryotic diversification [8, 9], although its function remains unknown in evolutionarily deep branching eukaryotes lacking canonical CTD heptad repeats. We used the ciliate protozoan Tetrahymena thermophila as a model organism whose genome encodes a highly divergent Rpb1 lacking canonical CTD heptad repeats. We endogenously tagged the Med31 subunit of the Mediator complex and performed affinity purification coupled with mass spectrometry (AP-MS) to identify Mediator subunits. We found that Med31 physically interacts with a large number of proteins (>20), several of which share similarities to canonical Mediator subunits in yeast and humans as well as Tetrahymena-specific proteins. Furthermore, Med31 ChIP-seq analysis suggested a global role for Mediator in transcription regulation. We demonstrated that MED31 knockdown in growing Tetrahymena results in the ectopic expression of developmental genes important for programmed DNA rearrangements. In addition, indirect immunofluorescence revealed Med31 localization in meiotic micronuclei, implicating Mediator in RNAPII-dependent ncRNA transcription. Our results reveal structural and functional insights and implicate Mediator as an ancient cellular machinery for transcription regulation with a possible involvement in global transcription of ncRNAs.
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Affiliation(s)
- Jyoti Garg
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Alejandro Saettone
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
| | - Syed Nabeel-Shah
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Matthew Cadorin
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
| | - Marcelo Ponce
- SciNet HPC Consortium, University of Toronto, 661 University Avenue, Suite 1140, Toronto, ON M5G 1M1, Canada
| | - Susanna Marquez
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Shuye Pu
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jack Greenblatt
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jean-Philippe Lambert
- Department of Molecular Medicine and Cancer Research Centre, Université Laval, Quebec, QC, Canada; CHU de Québec Research Center, CHUL, 2705 Laurier Boulevard, Quebec, QC G1V 4G2, Canada
| | - Ronald E Pearlman
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada.
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Kaczanowski A, Kiersnowska M. Formation and degradation of large extrusion bodies in Tetrahymena thermophila: The role of intramacronuclear microtubules in chromatin segregation. Eur J Protistol 2018; 66:177-188. [DOI: 10.1016/j.ejop.2018.09.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 09/19/2018] [Accepted: 09/24/2018] [Indexed: 11/17/2022]
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Abstract
Nuclear dualism is a characteristic feature of the ciliated protozoa. Tetrahymena have two different nuclei in each cell. The larger, polyploid, somatic macronucleus (MAC) is the site of transcriptional activity in the vegetatively growing cell. The smaller, diploid micronucleus (MIC) is transcriptionally inactive in vegetative cells, but is transcriptionally active in mating cells and responsible for the genetic continuity during sexual reproduction. Although the MICs and MACs develop from mitotic products of a common progenitor and reside in a common cytoplasm, they are different from one another in almost every respect.
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Affiliation(s)
- Kathleen M Karrer
- Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin, USA
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Slade KM, Freggiaro S, Cottrell KA, Smith JJ, Wiley EA. Sirtuin-mediated nuclear differentiation and programmed degradation in Tetrahymena. BMC Cell Biol 2011; 12:40. [PMID: 21933443 PMCID: PMC3191509 DOI: 10.1186/1471-2121-12-40] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Accepted: 09/21/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The NAD(+)-dependent histone deacetylases, known as "sirtuins", participate in a variety of processes critical for single- and multi-cellular life. Recent studies have elucidated the importance of sirtuin activity in development, aging, and disease; yet, underlying mechanistic pathways are not well understood. Specific sirtuins influence chromatin structure and gene expression, but differences in their pathways as they relate to distinct chromatin functions are just beginning to emerge. To further define the range of global chromatin changes dependent on sirtuins, unique biological features of the ciliated protozoan Tetrahymena thermophila can be exploited. This system offers clear spatial and temporal separation of multiple whole genome restructuring events critical for the life cycle. RESULTS Inhibition with nicotinamide revealed that sirtuin deacetylase activity in Tetrahymena cells promotes chromatin condensation during meiotic prophase, differentiation of heterochromatin from euchromatin during development, and chromatin condensation/degradation during programmed nuclear death. We identified a class I sirtuin, called Thd14, that resides in mitochondria and nucleoli during vegetative growth, and forms a large sub-nuclear aggregate in response to prolonged cell starvation that may be peripherally associated with nucleoli. During sexual conjugation and development Thd14 selectively concentrates in the parental nucleus prior to its apoptotic-like degradation. CONCLUSIONS Sirtuin activity is important for several functionally distinct events requiring global chromatin condensation. Our findings suggest a novel role for sirtuins in promoting programmed pycnosis by acting on chromatin destined for degradation. The sirtuin Thd14, which displays physiological-dependent differential localization within the nucleus, is a candidate for a chromatin condensation enzyme that is coupled to nuclear degradation.
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Affiliation(s)
- Kristin M Slade
- Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges, WM Keck Science Center, Claremont, CA 91711, USA
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A class II histone deacetylase acts on newly synthesized histones in Tetrahymena. EUKARYOTIC CELL 2008; 7:471-82. [PMID: 18178773 DOI: 10.1128/ec.00409-07] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Newly synthesized histones are acetylated prior to their deposition into nucleosomes. Following nucleosome formation and positioning, they are rapidly deacetylated, an event that coincides with further maturation of the chromatin fiber. The histone deacetylases (HDACs) used for histone deposition and de novo chromatin formation are poorly understood. In the ciliate Tetrahymena thermophila, transcription-related deacetylation in the macronucleus is physically separated from deposition-related deacetylation in the micronucleus. This feature was utilized to identify an HDAC named Thd2, a class II HDAC that acts on newly synthesized histones to remove deposition-related acetyl moieties. The THD2 transcript is alternatively spliced, and the major form contains a putative inositol polyphosphate kinase (IPK) domain similar to Ipk2, an enzyme that promotes chromatin remodeling by SWI/SNF remodeling complexes. Cells lacking Thd2, which retain deposition-related acetyl moieties on new histones, exhibit chromatin and cytological phenotypes indicative of a role for Thd2 in chromatin maturation, including the proteolytic processing of histone H3.
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Parker K, Maxson J, Mooney A, Wiley EA. Class I histone deacetylase Thd1p promotes global chromatin condensation in Tetrahymena thermophila. EUKARYOTIC CELL 2007; 6:1913-24. [PMID: 17715364 PMCID: PMC2043386 DOI: 10.1128/ec.00217-07] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Class I histone deacetylases (HDACs) regulate DNA-templated processes such as transcription. They act both at specific loci and more generally across global chromatin, contributing to acetylation patterns that may underlie large-scale chromatin dynamics. Although hypoacetylation is correlated with highly condensed chromatin, little is known about the contribution of individual HDACs to chromatin condensation mechanisms. Using the ciliated protozoan Tetrahymena thermophila, we investigated the role of a specific class I HDAC, Tauhd1p, in the reversible condensation of global chromatin. In this system, the normal physiological response to cell starvation includes the widespread condensation of the macronuclear chromatin and general repression of gene transcription. We show that the chromatin in Thd1p-deficient cells failed to condense during starvation. The condensation failure correlated with aberrant hyperphosphorylation of histone H1 and the overexpression of CDC2, encoding the major histone H1 kinase. Changes in the rate of acetate turnover on core histones and in the distribution of acetylated lysines 9 and 23/27 on histone H3 isoforms that were found to correlate with normal chromatin condensation were absent from Thd1p mutant cells. These results point to a role for a class I HDAC in the formation of reversible higher-order chromatin structures and global genome compaction through mechanisms involving the regulation of H1 phosphorylation and core histone acetylation/deacetylation kinetics.
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Affiliation(s)
- Kathryn Parker
- Joint Science Department, W M Keck Science Center, Claremont, CA 91711, USA
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Cervantes MD, Coyne RS, Xi X, Yao MC. The condensin complex is essential for amitotic segregation of bulk chromosomes, but not nucleoli, in the ciliate Tetrahymena thermophila. Mol Cell Biol 2006; 26:4690-700. [PMID: 16738332 PMCID: PMC1489118 DOI: 10.1128/mcb.02315-05] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The macronucleus of the binucleate ciliate Tetrahymena thermophila contains fragmented and amplified chromosomes that do not have centromeres, eliminating the possibility of mitotic nuclear division. Instead, the macronucleus divides by amitosis with random segregation of these chromosomes without detectable chromatin condensation. This amitotic division provides a special opportunity for studying the roles of mitotic proteins in segregating acentric chromatin. The Smc4 protein is a core component of the condensin complex that plays a role in chromatin condensation and has also been associated with nucleolar segregation, DNA repair, and maintenance of the chromatin scaffold. Mutants of Tetrahymena SMC4 have remarkable characteristics during amitosis. They do not form microtubules inside the macronucleus as normal cells do, and there is little or no bulk DNA segregation during cell division. Nevertheless, segregation of nucleoli to daughter cells still occurs, indicating the independence of this process and bulk DNA segregation in ciliate amitosis.
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Affiliation(s)
- Marcella D Cervantes
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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Cervantes MD, Xi X, Vermaak D, Yao MC, Malik HS. The CNA1 histone of the ciliate Tetrahymena thermophila is essential for chromosome segregation in the germline micronucleus. Mol Biol Cell 2005; 17:485-97. [PMID: 16251352 PMCID: PMC1345684 DOI: 10.1091/mbc.e05-07-0698] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Ciliated protozoans present several features of chromosome segregation that are unique among eukaryotes, including their maintenance of two nuclei: a germline micronucleus, which undergoes conventional mitosis and meiosis, and a somatic macronucleus that divides by an amitotic process. To study ciliate chromosome segregation, we have identified the centromeric histone gene in the Tetrahymena thermophila genome (CNA1). CNA1p specifically localizes to peripheral centromeres in the micronucleus but is absent in the macronucleus during vegetative growth. During meiotic prophase of the micronucleus, when chromosomes are stretched to twice the length of the cell, CNA1p is found localized in punctate spots throughout the length of the chromosomes. As conjugation proceeds, CNA1p appears initially diffuse, but quickly reverts to discrete dots in those nuclei destined to become micronuclei, whereas it remains diffuse and is gradually lost in developing macronuclei. In progeny of germline CNA1 knockouts, we see no defects in macronuclear division or viability of the progeny cells immediately following the knockout. However, within a few divisions, progeny show abnormal mitotic segregation of their micronucleus, with most cells eventually losing their micronucleus entirely. This study reveals a strong dependence of the germline micronucleus on centromeric histones for proper chromosome segregation.
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Affiliation(s)
- Marcella D Cervantes
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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