Human Genome Editing Science, Ethics, and Governance (2017) / Chapter Skim
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3 Basic Research Using Genome Editing
3 Basic Research Using Genome Editing
Pages 61-82
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From page 61... ...
The chapter then details how genome editing can be used in basic laboratory research aimed at advancing understanding of human cells and tissues; of human stem cells, diseases, and regenerative medicine; and of mammalian reproduction and development. Ethical and regulatory issues entailed in this research are then summarized.
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From page 62... ...
The complete set of genes in an organism is called its genome. Most human cells contain two complete copies of the human genome, each comprising 3 billion base pairs and encoding approximately 20,000 genes encoding proteins, plus the regulatory ele ments that control their expression.
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From page 63... ...
Among methods developed through the use of recombinant DNA technology is the ability to introduce DNA into cells where it can be expressed -- a so-called transgene. This method is widely used in fundamental laboratory research (see Appendix A for more detail)
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From page 64... ...
. They can be engineered by molecular biologists to recognize different short DNA sequences and can be joined to nucleases that cleave DNA.
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From page 65... ...
Figure 3-1 provides a summary of the ZFN, TALEN, and CRISPR methods of genome editing. As mentioned, these genome-editing methods are being widely applied across a broad range of biological sciences, from fundamental laboratory research on cells and laboratory animals; to applications in agriculture involving improvements in crop plants and farm animals; to applications in human health, both at the research level and, increasingly, in clinical applications.
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From page 66... ...
is targeted to a specific site on the DNA by the guide RNA (purple) , which binds a 20-base sequence in the genome adjacent to a short protospacer adjacent motif (PAM)
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From page 67... ...
In addition to these applications, this chapter reviews the potential for using similar approaches in basic research on human germline cells, not for the purposes of procreation but solely for laboratory research. This work will provide valuable insights into the processes of early human development and reproductive success, and could lead to clinical benefits, directly as a result of work with human embryos and germline cells or through improvements in the derivation and maintenance of stem cells in vitro.
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From page 68... ...
As can be seen from this brief survey, the rapidly developing versatility of these RNA-guided genome-editing systems is opening up numerous means of manipulating the expression and function of genes. A recent report of methods for inducibly knocking down or knocking out genes in a multiplex fashion in many cell types, including human pluripotent stem cells, as well as in mice (Bertero et al., 2016)
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From page 69... ...
Such pluripotent stem cells can be cultured in vitro and induced to develop into many different cell types, such as neurons, muscle or skin cells, and many others. Advances over the past several decades in understanding stem cells and how they can be used form the foundation for the field of regenerative medicine, which seeks to repair or replace damaged cells within human tissues or to generate new tissues after disease or injury.
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From page 70... ...
. BASIC LABORATORY RESEARCH TO ADVANCE UNDERSTANDING OF MAMMALIAN REPRODUCTION AND DEVELOPMENT Germline cells are cells with the capacity to be involved in forming a new individual and to have their genetic material passed on to a new generation.
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From page 71... ...
There are a number of ways to undertake these genetic manipulations and a number of cell types in which they can be conducted. The cell types below are all considered part of the germline or have the capacity to contribute to the germline: • embryonic stem cells derived from normal early embryos (blastocyst stages)
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From page 72... ...
Most embryo research has been conducted on mouse embryos, which are similar to human embryos in certain respects but significantly different in others (see Box 3-2)
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From page 73... ...
Pluripotent stem cells arise from the early embryo, and these cells can generate ES cells in culture. Better understanding of human embryonic development would provide insights into the origins and regulation of pluripotency and how to translate that knowledge into improved stem cells for regenerative medicine.
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From page 74... ...
. The abil ity to create iPS cells represents an example in which basic laboratory research contributed to critical advances in a field -- in this case regenerative medicine.
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From page 75... ...
(B) The trophectoderm of the human blastocyst does not stay in close contact with the epiblast after implantation but invades into the endometrium, where it will later form the cho rionic villi.
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From page 76... ...
In some cases, there could be interest in exploring the effects of altering specific genes at the next stages of human development, notably the early stages after the embryo would implant in a uterus. At present, culture of human embryos up to the stage just prior to germ-layer formation (at 14 days after fertilization or the formation of the "primitive streak")
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From page 77... ...
Such research also should lead to better ways of establishing and maintaining stem cells from these early embryonic stages, which could facilitate efforts to derive cell types for studies and treatments of disease and traumatic injury. Knowledge gained from these laboratory studies using genome-editing methods in early human embryos should also provide information about the suitability of these methods for any eventual
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From page 78... ...
Possible improvements in contraception Improved culture of early human embryos Improvements in IVF and PGD Insights into reasons for miscarriages and congenital malformations Development of extraembryonic tissues Insights into reasons for failures in (yolk sac and placenta) implantation and for miscarriages Isolation and in vitro differentiation of In vitro models for human diseases for pluripotent stem cells experimental testing of drugs and other therapies Improved cells for somatic gene/cell therapies and for regenerative medicine Investigations of sperm and oocyte Possible novel approaches to infertility development potential clinical use.
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From page 79... ...
. Human gametes have not yet been generated successfully from pluripotent stem cells, although two recent papers report the generation of early germ cell progenitors from human ES cells (Irie et al., 2015; Sasaki et al., 2015)
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From page 80... ...
ETHICAL AND REGULATORY ISSUES IN BASIC RESEARCH As described in more detail in Chapter 2, basic science research performed in the laboratory on somatic cells will be subject to regulation focused on safety for laboratory workers and the environment, including special review by institutional biosafety committees for work involving recombinant DNA. Few new ethical issues are raised, although if the cells and tissues come from identifiable living individuals, donor consent and privacy will be a concern, and in most cases the protocols will be subject to at least some review by institutional review boards.
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From page 81... ...
Important scientific and clinical issues relevant to human fertility and reproduction require continued laboratory research on human gametes and their progenitors, human embryos, and pluripotent stem cells. This research is necessary for medical and scientific purposes that are not directed at heritable genome editing, though it will also pro
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From page 82... ...
RECOMMENDATION 3-1. Existing regulatory infrastructure and processes for reviewing and evaluating basic laboratory genome editing research with human cells and tissues should be used to evaluate future basic laboratory research on human genome editing.
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