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Matsuzaki S, Sakuma T, Yamamoto T. REMOVER-PITCh: microhomology-assisted long-range gene replacement with highly multiplexed CRISPR-Cas9. In Vitro Cell Dev Biol Anim 2024; 60:697-707. [PMID: 38334880 PMCID: PMC11297102 DOI: 10.1007/s11626-024-00850-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 01/02/2024] [Indexed: 02/10/2024]
Abstract
A variety of CRISPR-Cas9-based gene editing technologies have been developed, including gene insertion and gene replacement, and applied to the study and treatment of diseases. While numerous studies have been conducted to improve the efficiency of gene insertion and to expand the system in various ways, there have been relatively few reports on gene replacement technology; therefore, further improvements are still needed in this context. Here, we developed the REMOVER-PITCh system to establish an efficient long-range gene replacement method and demonstrated its utility at two genomic loci in human cultured cells. REMOVER-PITCh depends on microhomology-assisted gene insertion technology called PITCh with highly multiplexed CRISPR-Cas9. First, we achieved gene replacement of about 20-kb GUSB locus using this system. Second, by applying the previously established knock-in-enhancing platform, the LoAD system, along with REMOVER-PITCh, we achieved the replacement of a longer gene region of about 200 kb at the ARSB locus. Our REMOVER-PITCh system will make it possible to remove and incorporate a variety of sequences from and into the genome, respectively, which will facilitate the generation of various disease and humanized models.
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Affiliation(s)
- Shu Matsuzaki
- Division of Integrated Sciences for Life, Graduate School of Integrated Sciences for Life, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan
- Drug Discovery Laboratory, Wakunaga Pharmaceutical Co., Ltd., 1624 Shimokotachi, Koda-Cho, Akitakata-Shi, Hiroshima, 739-1195, Japan
| | - Tetsushi Sakuma
- Division of Integrated Sciences for Life, Graduate School of Integrated Sciences for Life, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
| | - Takashi Yamamoto
- Division of Integrated Sciences for Life, Graduate School of Integrated Sciences for Life, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan
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2
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Truong DM. Writing the dark matter of the human genome into mice to better replicate human disease. Synth Biol (Oxf) 2024; 9:ysae003. [PMID: 38292445 PMCID: PMC10825503 DOI: 10.1093/synbio/ysae003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 01/11/2024] [Indexed: 02/01/2024] Open
Affiliation(s)
- David M Truong
- Department of Biomedical Engineering, NYU Tandon School of Engineering, Brooklyn, NY 11201, USA
- Department of Pathology, NYU Langone Health, New York, NY 10016, USA
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3
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Ohno T, Nakane T, Akase T, Kurasawa H, Aizawa Y. Development of an isogenic human cell trio that models polyglutamine disease. Genes Genet Syst 2023; 98:179-189. [PMID: 37821389 DOI: 10.1266/ggs.22-00030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/13/2023] Open
Abstract
Polyglutamine (polyQ) diseases are rare autosomal-dominant neurodegenerative diseases associated with the expansion of glutamine-encoding triplet repeats in certain genes. To investigate the functional influence of repeat expansion on disease mechanisms, we applied a biallelic genome-engineering platform that we recently established, called Universal Knock-in System or UKiS, to develop a human cell trio, a set of three isogenic cell lines that are homozygous for two different numbers of repeats (first and second lines) or heterozygous for the two repeat numbers (third line). As an example of a polyQ disease, we chose spinocerebellar ataxia type 2 (SCA2). In a pseudodiploid human cell line, both alleles of the glutamine-encoding triplet repeat in the SCA2-causing gene, ataxin 2 or ATXN2, were first knocked in with a donor sequence encoding both thymidine kinase and either puromycin or blasticidin resistance proteins under dual drug selection. The knocked-in donor alleles were then substituted with a payload having either 22 or 76 triplet repeats in ATXN2 by ganciclovir negative selection. The two-step substitution and subsequent SNP typing and genomic sequencing confirmed that the SCA2-modeling isogenic cell trio was obtained: three clones of 22-repeat homozygotes, two clones of 22/76-repeat heterozygotes and two clones of 76-repeat homozygotes. Finally, RT-PCR and immunoblotting using the obtained clones showed that, consistent with previous observations, glutamine tract expansion reduced transcriptional and translational expression of ATXN2. The cell clones with homozygous long-repeat alleles, which are rarely obtained from patients with SCA2, showed more drastic reduction of ATXN2 expression than the heterozygous clones. This study thus demonstrates the potential of UKiS, which is a beneficial platform for the efficient development of cell models not only for polyQ diseases but also for any other genetic diseases, which may accelerate our deeper understanding of disease mechanisms and cell-based screening for therapeutic drugs.
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Affiliation(s)
- Tomoyuki Ohno
- School of Life Science and Technology, Tokyo Institute of Technology
| | - Takeshi Nakane
- School of Life Science and Technology, Tokyo Institute of Technology
| | - Taichi Akase
- School of Life Science and Technology, Tokyo Institute of Technology
| | - Hikaru Kurasawa
- School of Life Science and Technology, Tokyo Institute of Technology
- Kanagawa Institute of Industrial Science and Technology
| | - Yasunori Aizawa
- School of Life Science and Technology, Tokyo Institute of Technology
- Kanagawa Institute of Industrial Science and Technology
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Kita Y, Okuzaki Y, Naoe Y, Lee J, Bang U, Okawa N, Ichiki A, Jonouchi T, Sakurai H, Kojima Y, Hotta A. Dual CRISPR-Cas3 system for inducing multi-exon skipping in DMD patient-derived iPSCs. Stem Cell Reports 2023; 18:1753-1765. [PMID: 37625413 PMCID: PMC10545483 DOI: 10.1016/j.stemcr.2023.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 07/30/2023] [Accepted: 07/31/2023] [Indexed: 08/27/2023] Open
Abstract
To restore dystrophin protein in various mutation patterns of Duchenne muscular dystrophy (DMD), the multi-exon skipping (MES) approach has been investigated. However, only limited techniques are available to induce a large deletion to cover the target exons spread over several hundred kilobases. Here, we utilized the CRISPR-Cas3 system for MES induction and showed that dual crRNAs could induce a large deletion at the dystrophin exon 45-55 region (∼340 kb), which can be applied to various types of DMD patients. We developed a two-color SSA-based reporter system for Cas3 to enrich the genome-edited cell population and demonstrated that MES induction restored dystrophin protein in DMD-iPSCs with three distinct mutations. Whole-genome sequencing and distance analysis detected no significant off-target deletion near the putative crRNA binding sites. Altogether, dual CRISPR-Cas3 is a promising tool to induce a gigantic genomic deletion and restore dystrophin protein via MES induction.
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Affiliation(s)
- Yuto Kita
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Yuya Okuzaki
- Nagoya University Graduate School of Bioagricultural Sciences, Avian Bioscience Research Center, Furo-cho, Chikusa-ku, Nagoya, Aishi 464-8601, Japan
| | - Youichi Naoe
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Joseph Lee
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Uikyu Bang
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Natsumi Okawa
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Akane Ichiki
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Tatsuya Jonouchi
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hidetoshi Sakurai
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Yusuke Kojima
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Akitsu Hotta
- Center for iPS Cell Research and Application, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; Takeda-CiRA Joint Program (T-CiRA), Fujisawa, Kanagawa 251-8555, Japan.
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Balmas E, Sozza F, Bottini S, Ratto ML, Savorè G, Becca S, Snijders KE, Bertero A. Manipulating and studying gene function in human pluripotent stem cell models. FEBS Lett 2023; 597:2250-2287. [PMID: 37519013 DOI: 10.1002/1873-3468.14709] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 07/04/2023] [Accepted: 07/05/2023] [Indexed: 08/01/2023]
Abstract
Human pluripotent stem cells (hPSCs) are uniquely suited to study human development and disease and promise to revolutionize regenerative medicine. These applications rely on robust methods to manipulate gene function in hPSC models. This comprehensive review aims to both empower scientists approaching the field and update experienced stem cell biologists. We begin by highlighting challenges with manipulating gene expression in hPSCs and their differentiated derivatives, and relevant solutions (transfection, transduction, transposition, and genomic safe harbor editing). We then outline how to perform robust constitutive or inducible loss-, gain-, and change-of-function experiments in hPSCs models, both using historical methods (RNA interference, transgenesis, and homologous recombination) and modern programmable nucleases (particularly CRISPR/Cas9 and its derivatives, i.e., CRISPR interference, activation, base editing, and prime editing). We further describe extension of these approaches for arrayed or pooled functional studies, including emerging single-cell genomic methods, and the related design and analytical bioinformatic tools. Finally, we suggest some directions for future advancements in all of these areas. Mastering the combination of these transformative technologies will empower unprecedented advances in human biology and medicine.
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Affiliation(s)
- Elisa Balmas
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Federica Sozza
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Sveva Bottini
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Maria Luisa Ratto
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Giulia Savorè
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Silvia Becca
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Kirsten Esmee Snijders
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
| | - Alessandro Bertero
- Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center "Guido Tarone", University of Turin, Torino, Italy
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Friedman CE, Fayer S, Pendyala S, Chien WM, Loiben A, Tran L, Chao LS, Mckinstry A, Ahmed D, Karbassi E, Fenix AM, Murry CE, Starita LM, Fowler DM, Yang KC. CRaTER enrichment for on-target gene editing enables generation of variant libraries in hiPSCs. J Mol Cell Cardiol 2023; 179:60-71. [PMID: 37019277 PMCID: PMC10208587 DOI: 10.1016/j.yjmcc.2023.03.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 03/14/2023] [Accepted: 03/29/2023] [Indexed: 04/07/2023]
Abstract
Standard transgenic cell line generation requires screening 100-1000s of colonies to isolate correctly edited cells. We describe CRISPRa On-Target Editing Retrieval (CRaTER) which enriches for cells with on-target knock-in of a cDNA-fluorescent reporter transgene by transient activation of the targeted locus followed by flow sorting to recover edited cells. We show CRaTER recovers rare cells with heterozygous, biallelic-editing of the transcriptionally-inactive MYH7 locus in human induced pluripotent stem cells (hiPSCs), enriching on average 25-fold compared to standard antibiotic selection. We leveraged CRaTER to enrich for heterozygous knock-in of a library of variants in MYH7, a gene in which missense mutations cause cardiomyopathies, and recovered hiPSCs with 113 different variants. We differentiated these hiPSCs to cardiomyocytes and show MHC-β fusion proteins can localize as expected. Additionally, single-cell contractility analyses revealed cardiomyocytes with a pathogenic, hypertrophic cardiomyopathy-associated MYH7 variant exhibit salient HCM physiology relative to isogenic controls. Thus, CRaTER substantially reduces screening required for isolation of gene-edited cells, enabling generation of functional transgenic cell lines at unprecedented scale.
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Affiliation(s)
- Clayton E Friedman
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Shawn Fayer
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Sriram Pendyala
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Wei-Ming Chien
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA; Cardiology/Hospital Specialty Medicine, VA Puget Sound HCS, Seattle, WA 98108, USA
| | - Alexander Loiben
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Linda Tran
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Leslie S Chao
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Ashley Mckinstry
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Dania Ahmed
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA
| | - Elaheh Karbassi
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Laboratory Medicine & Pathology, University of Washington, Seattle, WA 98109, USA
| | - Aidan M Fenix
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Laboratory Medicine & Pathology, University of Washington, Seattle, WA 98109, USA
| | - Charles E Murry
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA; Department of Laboratory Medicine & Pathology, University of Washington, Seattle, WA 98109, USA; Department of Bioengineering, University of Washington, Seattle, WA 98195, USA
| | - Lea M Starita
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA
| | - Douglas M Fowler
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA; Department of Bioengineering, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA
| | - Kai-Chun Yang
- Institute for Stem Cell and Regenerative Medicine, University of Washington, School of Medicine, Seattle, WA 98109, USA; Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109, USA; Department of Medicine/Cardiology, University of Washington, Seattle, WA 98109, USA; Cardiology/Hospital Specialty Medicine, VA Puget Sound HCS, Seattle, WA 98108, USA.
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7
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Friedman CE, Fayer S, Pendyala S, Chien WM, Tran L, Chao L, Mckinstry A, Karbassi E, Fenix AM, Loiben A, Murry CE, Starita LM, Fowler DM, Yang KC. CRaTER enrichment for on-target gene-editing enables generation of variant libraries in hiPSCs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.25.525582. [PMID: 36747685 PMCID: PMC9900876 DOI: 10.1101/2023.01.25.525582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/15/2023]
Abstract
Standard transgenic cell line generation requires screening 100-1000s of colonies to isolate correctly edited cells. We describe CR ISPR a On- T arget E diting R etrieval (CRaTER) which enriches for cells with on-target knock-in of a cDNA-fluorescent reporter transgene by transient activation of the targeted locus followed by flow sorting to recover edited cells. We show CRaTER recovers rare cells with heterozygous, biallelic-editing of the transcriptionally-inactive MYH7 locus in human induced pluripotent stem cells (hiPSCs), enriching on average 25-fold compared to standard antibiotic selection. We leveraged CRaTER to enrich for heterozygous knock-in of a library of single nucleotide variants (SNVs) in MYH7 , a gene in which missense mutations cause cardiomyopathies, and recovered hiPSCs with 113 different MYH7 SNVs. We differentiated these hiPSCs to cardiomyocytes and show MYH7 fusion proteins can localize as expected. Thus, CRaTER substantially reduces screening required for isolation of gene-edited cells, enabling generation of transgenic cell lines at unprecedented scale.
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Blanch-Asensio A, Grandela C, Brandão KO, de Korte T, Mei H, Ariyurek Y, Yiangou L, Mol MP, van Meer BJ, Kloet SL, Mummery CL, Davis RP. STRAIGHT-IN enables high-throughput targeting of large DNA payloads in human pluripotent stem cells. CELL REPORTS METHODS 2022; 2:100300. [PMID: 36313798 PMCID: PMC9606106 DOI: 10.1016/j.crmeth.2022.100300] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 07/12/2022] [Accepted: 08/31/2022] [Indexed: 04/20/2023]
Abstract
Inserting large DNA payloads (>10 kb) into specific genomic sites of mammalian cells remains challenging. Applications ranging from synthetic biology to evaluating the pathogenicity of disease-associated variants for precision medicine initiatives would greatly benefit from tools that facilitate this process. Here, we merge the strengths of different classes of site-specific recombinases and combine these with CRISPR-Cas9-mediated homologous recombination to develop a strategy for stringent site-specific replacement of genomic fragments at least 50 kb in size in human induced pluripotent stem cells (hiPSCs). We demonstrate the versatility of STRAIGHT-IN (serine and tyrosine recombinase-assisted integration of genes for high-throughput investigation) by (1) inserting various combinations of fluorescent reporters into hiPSCs to assess the excitation-contraction coupling cascade in derivative cardiomyocytes and (2) simultaneously targeting multiple variants associated with inherited cardiac arrhythmic disorders into a pool of hiPSCs. STRAIGHT-IN offers a precise approach to generate genetically matched panels of hiPSC lines efficiently and cost effectively.
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Affiliation(s)
- Albert Blanch-Asensio
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Catarina Grandela
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Karina O. Brandão
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Tessa de Korte
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Hailiang Mei
- Sequencing Analysis Support Core, Leiden University Medical Center, 2333RC Leiden, the Netherlands
| | - Yavuz Ariyurek
- Leiden Genome Technology Center, Leiden University Medical Center, 2333RC Leiden, the Netherlands
| | - Loukia Yiangou
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Mervyn P.H. Mol
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Berend J. van Meer
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
| | - Susan L. Kloet
- Leiden Genome Technology Center, Leiden University Medical Center, 2333RC Leiden, the Netherlands
| | - Christine L. Mummery
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
- Department of Applied Stem Cell Technologies, University of Twente, 7500AE Enschede, the Netherlands
| | - Richard P. Davis
- Department of Anatomy and Embryology, Leiden University Medical Center, 2300RC Leiden, the Netherlands
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