Gene editing using CRISPR-Cas9 technology: potential implications in assisted reproduction

PURPOSE OF REVIEW

This article reviews the mechanisms, advancements, and potential implications of clustered regularly interspaced short palindromic repeats-associated (CRISPR-Cas) gene editing technology, with a specific focus on its applications in reproductive biology and assisted reproduction. It aims to explore the benefits and challenges of integrating this revolutionary technology into clinical and research settings.

RECENT FINDINGS

CRISPR-Cas9 is a transformative tool for precise genome editing, enabling targeted modifications through mechanisms like nonhomologous end joining (NHEJ) and homology-directed repair (HDR). Innovations such as Cas9 nickase and dCas9 systems have improved specificity and expanded applications, including gene activation, repression, and epigenetic modifications. In reproductive research, CRISPR has facilitated gene function studies, corrected genetic mutations in animal models, and demonstrated potential in addressing human infertility and hereditary disorders. Emerging applications include mitochondrial genome editing, population control of disease vectors via gene drives, and detailed analyses of epigenetic mechanisms.

SUMMARY

CRISPR-Cas9 technology has revolutionized genetic engineering by enabling precise genome modifications. This article discusses its mechanisms, focusing on the repair pathways (NHEJ and HDR) and methods to mitigate off-target effects. In reproductive biology, CRISPR has advanced our understanding of fertility genes, allowed corrections of hereditary mutations, and opened avenues for novel therapeutic strategies. While its clinical application in human-assisted reproduction faces ethical and safety challenges, ongoing innovations hold promise for broader biomedical applications.

A comprehensive review on the current status of CRISPR based clinical trials for rare diseases

A considerable fraction of population in the world suffers from rare diseases. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and its related Cas proteins offer a modern form of curative gene therapy for treating the rare diseases. Hereditary transthyretin amyloidosis, hereditary angioedema, duchenne muscular dystrophy and Rett syndrome are a few examples of such rare diseases. CRISPR/Cas9, for example, has been used in the treatment of β-thalassemia and sickle cell disease (Frangoul et al., 2021; Pavani et al., 2021) [1,2]. Neurological diseases such as Huntington's have also been focused in some studies involving CRISPR/Cas (Yang et al., 2017; Yan et al., 2023) [3,4]. Delivery of these biologicals via vector and non vector mediated methods depends on the type of target cells, characteristics of expression, time duration of expression, size of foreign genetic material etc. For instance, retroviruses find their applicability in case of ex vivo delivery in somatic cells due to their ability to integrate in the host genome. These have been successfully used in gene therapy involving X-SCID patients although, incidence of inappropriate activation has been reported. On the other hand, ex vivo gene therapy for β-thalassemia involved use of BB305 lentiviral vector for high level expression of CRISPR biological in HSCs. The efficacy and safety of these biologicals will decide their future application as efficient genome editing tools as they go forward in further stages of human clinical trials. This review focuses on CRISPR/Cas based therapies which are at various stages of clinical trials for treatment of rare diseases and the constraints and ethical issues associated with them.

CRISPR-Based Gene Editing: a Modern Approach for Study and Treatment of Cancer

The development and emergence of clustered regularly interspaced short palindromic repeats (CRISPR) as a genome-editing technology have created a plethora of opportunities in genetic engineering. The ability of sequence-specific addition or removal of DNA in an efficient and cost-effective manner has revolutionized modern research in the field of life science and healthcare. CRISPR is widely used as a genome engineering tool in clinical studies for observing gene expression and metabolic pathway regulations in detail. Even in the case of transgenic research and personalized gene manipulation studies, CRISPR-based technology is used extensively. To understand and even to correct the underlying genetic problem is of cancer, CRISPR-based technology can be used. Various kinds of work is going on throughout the world which are attempting to target different genes in order to discover novel and effective methodologies for the treatment of cancer. In this review, we provide a brief overview on the application of CRISPR gene editing technology in cancer treatment focusing on the key aspects of cancer screening, modelling and therapy techniques.

Various repair events following CRISPR/Cas9-based mutational correction of an infertility-related mutation in mouse embryos

PURPOSE

Unpredictable genetic modifications and chromosomal aberrations following CRISPR/Cas9 administration hamper the efficacy of germline editing. Repair events triggered by double-strand DNA breaks (DSBs) besides non-homologous end joining and repair template-driven homology-directed repair have been insufficiently investigated in mouse. In this work, we are the first to investigate the precise repair mechanisms triggered by parental-specific DSB induction in mouse for paternal mutational correction in the context of an infertility-related mutation.

METHODS

We aimed to correct a paternal 22-nucleotide deletion in Plcz1, associated with lack of fertilisation in vitro, by administrating CRISPR/Cas9 components during intracytoplasmic injection of Plcz1-null sperm in wild-type oocytes combined with assisted oocyte activation. Through targeted next-generation sequencing, 77 injected embryos and 26 blastomeres from seven injected embryos were investigated. In addition, low-pass whole genome sequencing was successfully performed on 17 injected embryo samples.

RESULTS

Repair mechanisms induced by two different CRISPR/Cas9 guide RNA (gRNA) designs were investigated. In 13.73% (7/51; gRNA 1) and 19.05% (4/21; gRNA 2) of the targeted embryos, only the wild-type allele was observed, of which the majority (85.71%; 6/7) showed integrity of the targeted chromosome. Remarkably, for both designs, only in one of these embryos (1/7; gRNA 1 and 1/4; gRNA2) could repair template use be detected. This suggests that alternative repair events have occurred. Next, various genetic events within the same embryo were detected after single-cell analysis of four embryos.

CONCLUSION

Our results suggest the occurrence of mosaicism and complex repair events after CRISPR/Cas9 DSB induction where chromosomal integrity is predominantly contained.

Heritable genome editing: ethical aspects of a developing domain

In the past decade, scientific developments in human germline genome editing (GGE) have reinvigorated questions about research ethics, responsible innovation, and what it means to do good in the field of reproductive biology and medicine. In recent years, it has become part of the ethical debate on GGE whether categorical objections about (un)naturalness, dignity, respect for the gene pool as common heritage, are and should be supplemented by more pragmatic questions about safety, utility, efficacy, and potential 'misuse', which seem to become more dominant in the moral discussion. This mini-review summarizes the morally relevant aspects of the rapidly developing domain of GGE, focusing on reproductive applications and with special attention to the ethical questions pertaining to how this technology may affect the interests of those that come to be by means of it. While vital, this encompasses more than safety considerations. Taking this perspective, it will be crucial to engage with normative questions about how GGE maps on the importance of accommodating future parents' preference to have genetically related children, and how far we should go to facilitate this. Similarly, a comprehensive ethical debate about 'appropriate application' of GGE cannot shake off the more fundamental question about how notions like 'normalcy', 'quality of life', and 'disability' can be conceptualized. This is crucial in view of respecting persons whichever traits they have and in view of acceptable boundaries to parental responsibilities.

Retained chromosomal integrity following CRISPR-Cas9-based mutational correction in human embryos

Human germline gene correction by targeted nucleases holds great promise for reducing mutation transmission. However, recent studies have reported concerning observations in CRISPR-Cas9-targeted human embryos, including mosaicism and loss of heterozygosity (LOH). The latter has been associated with either gene conversion or (partial) chromosome loss events. In this study, we aimed to correct a heterozygous basepair substitution in PLCZ1, related to infertility. In 36% of the targeted embryos that originated from mutant sperm, only wild-type alleles were observed. By performing genome-wide double-digest restriction site-associated DNA sequencing, integrity of the targeted chromosome (i.e., no deletions larger than 3 Mb or chromosome loss) was confirmed in all seven targeted GENType-analyzed embryos (mutant editing and absence of mutation), while short-range LOH events (shorter than 10 Mb) were clearly observed by single-nucleotide polymorphism assessment in two of these embryos. These results fuel the currently ongoing discussion on double-strand break repair in early human embryos, making a case for the occurrence of gene conversion events or partial template-based homology-directed repair.

Biomaterial-based gene therapy

Gene therapy, a medical approach that involves the correction or replacement of defective and abnormal genes, plays an essential role in the treatment of complex and refractory diseases, such as hereditary diseases, cancer, and rheumatic immune diseases. Nucleic acids alone do not easily enter the target cells due to their easy degradation in vivo and the structure of the target cell membranes. The introduction of genes into biological cells is often dependent on gene delivery vectors, such as adenoviral vectors, which are commonly used in gene therapy. However, traditional viral vectors have strong immunogenicity while also presenting a potential infection risk. Recently, biomaterials have attracted attention for use as efficient gene delivery vehicles, because they can avoid the drawbacks associated with viral vectors. Biomaterials can improve the biological stability of nucleic acids and the efficiency of intracellular gene delivery. This review is focused on biomaterial-based delivery systems in gene therapy and disease treatment. Herein, we review the recent developments and modalities of gene therapy. Additionally, we discuss nucleic acid delivery strategies, with a focus on biomaterial-based gene delivery systems. Furthermore, the current applications of biomaterial-based gene therapy are summarized.

Mapping the 'Ethical' Controversy of Human Heritable Genome Editing: a Multidisciplinary Approach

Genome editing, for instance by CRISPR-Cas, is a major advancement of the last 10 years in medicine but questions ethically our practices. In particular, human embryo heritable genome editing is a source of great controversy. We explored how this ethical question was debated in the literature from PubMed database, in a period of 4 years (2016-2020) around the announcement of the 'CRISPR babies' Chinese experiment in November 2018. We evaluated the weight of the arguments for and against this topic, through an analysis of reviews published on this question. The most important arguments come from the technical perspective: safety issues and benefits, putative long-term effects on the future generations and the need to assess this aspect. Next, foreseeable clinical benefits and the alternatives to these methods are discussed. The number of people that would benefit from such techniques is also considered. However, social and anthropological issues are addressed in a more disparate way. Parenthood and desire for children are sometimes overlooked. Few authors mention social justice, stigmatisation and equality of access. Consent and information are more clearly addressed, as well as the question of the relationship between generations. Finally, the effects on the nature of humankind or human species are far from being consensual; the risks of enhancement, eugenics and transhumanism are raised. We conclude that the risks associated with the immaturity of the technique were at the forefront of the ethical debate on human embryo heritable genome editing. Their consequences were seen as more immediate and easier to handle than those of sociological or anthropological projections, which are more speculative in nature.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41649-022-00234-1.

Ethical Perspectives of Therapeutic Human Genome Editing From Multiple and Diverse Viewpoints: A Scoping Review

Human genome editing has been increasingly explored to determine if it can be used to eradicate genetic diseases like sickle cell disease, but it has also been surrounded by a wide variety of ethical dilemmas. The purpose of this review was to conduct a scoping review of the ethics of therapeutic human genome editing in terms of philosophy, theology, public perspectives, and research ethics. A systemized search of PubMed, Embase, Ovid MEDLINE, and Web of Science was conducted. The initial search resulted in 4,445 articles, and after removing 1,750 duplicates and screening the remaining 2,695 articles, 27 final articles were selected for the final analysis. From a philosophical and theological standpoint, therapeutic human genome editing was generally ethically acceptable. Worldwide public perspectives were also in agreement except for the Oceanic region, which disagreed mainly due to the possible effects on future generations. Lastly, human research ethics revealed that women were not always included in informed consent, and that child autonomy needs to be preserved. Further research is needed to determine adverse effects on the mother, fetus, and future generations.

CRISPR/Cas gene editing in the human germline

The ease and efficacy of CRISPR/Cas9 germline gene editing in animal models paved the way to human germline gene editing (HGGE), by which permanent changes can be introduced into the embryo. Distinct genes can be knocked out to examine their function during embryonic development. Alternatively, specific sequences can be introduced which can be applied to correct disease-causing mutations. To date, it has been shown that the success of HGGE is dependent on various experimental parameters and that various hurdles (i.e. loss-of-heterozygosity and mosaicism) need to be overcome before clinical applications should be considered. Due to the shortage of human germline material and the ethical constraints concerning HGGE, alternative models such as stem cells have been evaluated as well, in terms of their predictive value on the genetic outcome for HGGE approaches. This review will give an overview of the state of the art of HGGE in oocytes and embryos, and its accompanying challenges.

Genetics Matters: Voyaging from the Past into the Future of Humanity and Sustainability

The understanding of how genetic information may be inherited through generations was established by Gregor Mendel in the 1860s when he developed the fundamental principles of inheritance. The science of genetics, however, began to flourish only during the mid-1940s when DNA was identified as the carrier of genetic information. The world has since then witnessed rapid development of genetic technologies, with the latest being genome-editing tools, which have revolutionized fields from medicine to agriculture. This review walks through the historical timeline of genetics research and deliberates how this discipline might furnish a sustainable future for humanity.

Funding CRISPR: Understanding the role of government and philanthropic institutions in supporting academic research within the CRISPR innovation system

CRISPR/Cas has the potential to revolutionize medicine, agriculture, and biology. Understanding the trajectory of CRISPR research, how it is influenced and who pays for it, is an essential research policy question. We use a combination of methods to map, via quantitative content analysis of CRISPR papers, the research funding profile of major government agencies and organizations philanthropic, and the networks involved in supporting key stages of high-influence research, namely basic biological research and technological development. The results of the content analysis show how the research supported by the main US government agencies focus both on the study of CRISPR as a biological phenomenon and on its technological development and use as a biomedical research tool. US philanthropic organizations with the exception of HHMI, tend, by contrast, to specialize in funding CRISPR as a genome editing technology. We present a model of co-funding networks at the two most prominent institutions for CRISPR/Cas research, the University of California and the Harvard/MIT/Broad Institute, to illuminate how philanthropic organizations have articulated with government agencies to co-finance the discovery and development of CRISPR/Cas. Our results raise fundamental questions about the role of the state and the influence of philanthropy over the trajectory of transformative technologies.

Peer Review

https://publons.com/publon/10.1162/qss_a_00187

Ethical considerations of preconception and prenatal gene modification in the embryo and fetus

The National Academies of Sciences and Medicine 2020 consensus statement advocates the reinstatement of research in preconception heritable human genome editing (HHGE), despite the ethical concerns that have been voiced about interventions in the germline, and outlines criteria for its eventual clinical application to address monogenic disorders. However, the statement does not give adequate consideration to alternative technologies. Importantly, it omits comparison to fetal gene therapy (FGT), which involves gene modification applied prenatally to the developing fetus and which is better researched and less ethically contentious. While both technologies are applicable to the same monogenic diseases causing significant prenatal or early childhood morbidity, the benefits and risks of HHGE are distinct from FGT though there are important overlaps. FGT has the current advantage of a wealth of robust preclinical data, while HHGE is nascent technology and its feasibility for specific diseases still requires scientific proof. The ethical concerns surrounding each are unique and deserving of further discussion, as there are compelling arguments supporting research and eventual clinical translation of both technologies. In this Opinion, we consider HHGE and FGT through technical and ethical lenses, applying common ethical principles to provide a sense of their feasibility and acceptability. Currently, FGT is in a more advanced position for clinical translation and may be less ethically contentious than HHGE, so it deserves to be considered as an alternative therapy in further discussions on HHGE implementation.

Heritable human genome editing: Research progress, ethical considerations, and hurdles to clinical practice

Our genome at conception determines much of our health as an adult. Most human diseases have a heritable component and thus may be preventable through heritable genome editing. Preventing disease from the beginning of life before irreversible damage has occurred is an admirable goal, but the path to fruition remains unclear. Here, we review the significant scientific contributions to the field of human heritable genome editing, the unique ethical challenges that cannot be overlooked, and the hurdles that must be overcome prior to translating these technologies into clinical practice.

The role of CRISPR-Cas in advancing precision periodontics

The significant advancement of molecular biology has revolutionized medicine and provided important technologies to further clinical research development. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) are DNA sequences derived from bacteriophages which have previously infected the bacterial species. The CRISPR-Cas system plays a key role in bacterial defense by detecting and destroying DNA fragments during subsequent bacteriophage invasions. The Cas9 enzyme recognizes and cleaves new invading CRISPR-complementary DNA sequences. Researchers have taken advantage of this biological device to manipulate microbes' genes and develop novel therapeutics to tackle systemic disease. In this review, we discuss the potential of utilizing CRISPR-Cas systems in the periodontal field to develop personalized periodontal care. We summarize promising attempts to bring this technology to the clinical setting. Finally, we provide insights regarding future developments to best utilize the CRISPR-Cas systems to advance precision periodontics. Although further research is imperative to evaluate the safety and potential of using CRISPR-Cas to develop precision periodontics approaches, few studies showed promising data to support the investment into this important technology in the dental sector. CRISPR-Cas9 can be a useful tool to create knockouts in vitro and in vivo as a screening tool to identify cellular pathways involved in the pathogenesis of periodontitis. Alternative CRISPR systems such as CRISPRa, CRISPRi, and Cas13 can be used to modify the transcriptome and gene expression of genes involved in periodontitis progression. CRISPR systems such as Cas3 can be used to target the periodontal biofilm and to develop new strategies to reduce or eliminate periodontal pathogens. Currently, the utility of CRISPR-Cas applications in clinical settings is limited. Through this review, we hope to foster further discussion in the periodontal research and clinical communities with respect to the potential clinical application of novel, CRISPR-Cas based, therapeutics for periodontitis.

The genome editing revolution: review

BACKGROUND

Development of efficient strategies has always been one of the great perspectives for biotechnologists. During the last decade, genome editing of different organisms has been a fast advancing field and therefore has received a lot of attention from various researchers comprehensively reviewing latest achievements and offering opinions on future directions. This review presents a brief history, basic principles, advantages and disadvantages, as well as various aspects of each genome editing technology including the modes, applications, and challenges that face delivery of gene editing components.

MAIN BODY

Genetic modification techniques cover a wide range of studies, including the generation of transgenic animals, functional analysis of genes, model development for diseases, or drug development. The delivery of certain proteins such as monoclonal antibodies, enzymes, and growth hormones has been suffering from several obstacles because of their large size. These difficulties encouraged scientists to explore alternative approaches, leading to the progress in gene editing. The distinguished efforts and enormous experimentation have now been able to introduce methodologies that can change the genetic constitution of the living cell. The genome editing strategies have evolved during the last three decades, and nowadays, four types of "programmable" nucleases are available in this field: meganucleases, zinc finger nucleases, transcription activator-like effector nucleases, and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas-9) system. Each group has its own characteristics necessary for researchers to select the most suitable method for gene editing tool for a range of applications. Genome engineering/editing technology will revolutionize the creation of precisely manipulated genomes of cells or organisms in order to modify a specific characteristic. Of the potential applications are those in human health and agriculture. Introducing constructs into target cells or organisms is the key step in genome engineering.

CONCLUSIONS

Despite the success already achieved, the genome editing techniques are still suffering certain difficulties. Challenges must be overcome before the full potential of genome editing can be realized.

The genome editing revolution: review

BACKGROUND

Development of efficient strategies has always been one of the great perspectives for biotechnologists. During the last decade, genome editing of different organisms has been a fast advancing field and therefore has received a lot of attention from various researchers comprehensively reviewing latest achievements and offering opinions on future directions. This review presents a brief history, basic principles, advantages and disadvantages, as well as various aspects of each genome editing technology including the modes, applications, and challenges that face delivery of gene editing components.

MAIN BODY

Genetic modification techniques cover a wide range of studies, including the generation of transgenic animals, functional analysis of genes, model development for diseases, or drug development. The delivery of certain proteins such as monoclonal antibodies, enzymes, and growth hormones has been suffering from several obstacles because of their large size. These difficulties encouraged scientists to explore alternative approaches, leading to the progress in gene editing. The distinguished efforts and enormous experimentation have now been able to introduce methodologies that can change the genetic constitution of the living cell. The genome editing strategies have evolved during the last three decades, and nowadays, four types of "programmable" nucleases are available in this field: meganucleases, zinc finger nucleases, transcription activator-like effector nucleases, and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas-9) system. Each group has its own characteristics necessary for researchers to select the most suitable method for gene editing tool for a range of applications. Genome engineering/editing technology will revolutionize the creation of precisely manipulated genomes of cells or organisms in order to modify a specific characteristic. Of the potential applications are those in human health and agriculture. Introducing constructs into target cells or organisms is the key step in genome engineering.

CONCLUSIONS

Despite the success already achieved, the genome editing techniques are still suffering certain difficulties. Challenges must be overcome before the full potential of genome editing can be realized.

Human germline editing in the era of CRISPR-Cas: risk and uncertainty, inter-generational responsibility, therapeutic legitimacy

BACKGROUND

Clustered Regularly Interspaced Short Palindromic Repeats-associated (CRISPR-Cas) technology may allow for efficient and highly targeted gene editing in single-cell embryos. This possibility brings human germline editing into the focus of ethical and legal debates again.

MAIN BODY

Against this background, we explore essential ethical and legal questions of interventions into the human germline by means of CRISPR-Cas: How should issues of risk and uncertainty be handled? What responsibilities arise regarding future generations? Under which conditions can germline editing measures be therapeutically legitimized? For this purpose, we refer to a scenario anticipating potential further development in CRISPR-Cas technology implying improved accuracy and exclusion of germline transmission to future generations. We show that, if certain concepts regarding germline editing are clarified, under such conditions a categorical prohibition of one-generation germline editing of single-cell embryos appears not to be ethically or legally justifiable.

CONCLUSION

These findings are important prerequisites for the international debate on the ethical and legal justification of germline interventions in the human embryo as well as for the harmonization of international legal standards.

RUNX2-modifying enzymes: therapeutic targets for bone diseases

RUNX2 is a master transcription factor of osteoblast differentiation. RUNX2 expression in the bone and osteogenic front of a suture is crucial for cranial suture closure and membranous bone morphogenesis. In this manner, the regulation of RUNX2 is precisely controlled by multiple posttranslational modifications (PTMs) mediated by the stepwise recruitment of multiple enzymes. Genetic defects in RUNX2 itself or in its PTM regulatory pathways result in craniofacial malformations. Haploinsufficiency in RUNX2 causes cleidocranial dysplasia (CCD), which is characterized by open fontanelle and hypoplastic clavicles. In contrast, gain-of-function mutations in FGFRs, which are known upstream stimulating signals of RUNX2 activity, cause craniosynostosis (CS) characterized by premature suture obliteration. The identification of these PTM cascades could suggest suitable drug targets for RUNX2 regulation. In this review, we will focus on the mechanism of RUNX2 regulation mediated by PTMs, such as phosphorylation, prolyl isomerization, acetylation, and ubiquitination, and we will summarize the therapeutics associated with each PTM enzyme for the treatment of congenital cranial suture anomalies.

Harnessing the potential of CRISPR-based platforms to advance the field of hospital medicine

INTRODUCTION

Clustered regularly interspaced short palindromic repeats (CRISPR) are segments of nucleic acid that play a role in prokaryotic defense and form the basis of a genome editing technology that allows permanent alteration of genetic material. This methodology, known as CRISPR-Cas9, is poised to revolutionize molecular biology, but no literature yet exists on how these advances will affect hospitalists.

AREAS COVERED

These specialists in inpatient medicine care for a wide variety of hospitalized patients, including those with infectious disease, cancer, cardiovascular disease, autoimmune disease, hematologic disease, and a variety of other conditions that may soon be impacted by advances in gene-modifying technology provided by CRISPR-Cas9. A Literature search was performed using PubMed [1 December 2019-17 April 2020].

EXPERT OPINION

This paper reviews the remarkable diagnostic and therapeutic potential of the CRISPR-Cas9 platform and concludes with a look at ethical issues and technical hurdles pertaining to the implementation of permanent gene modification in the practice of Hospital Medicine.

Lysosomal storage diseases: current therapies and future alternatives

Lysosomal storage disorders (LSDs) are a group of monogenic diseases characterized by progressive accumulation of undegraded substrates into the lysosome, due to mutations in genes that encode for proteins involved in normal lysosomal function. In recent years, several approaches have been explored to find effective and successful therapies, including enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, hematopoietic stem cell transplantation, and gene therapy. In the case of gene therapy, genome editing technologies have opened new horizons to accelerate the development of novel treatment alternatives for LSD patients. In this review, we discuss the current therapies for this group of disorders and present a detailed description of major genome editing technologies, as well as the most recent advances in the treatment of LSDs. We will further highlight the challenges and current bioethical debates of genome editing.

Affected Genome Editing Crops: The Consequences of Genome-Edited Babies in China

Though genome editing (GE) is a powerful technology, germline GE engineering is strongly objectionable for a huge ethical challenge. The after-effects of the genome-edited babies incident have been emerging in China, whether technology or ethics. It is very noticeable that the case has been adverse effects on the application of GE technology in other fields, especially in GE crops. After the incident, research and development of GE crops was affected obviously. It is clear that GE crops and other basic research and application related to GE technology should be encouraged and should not be treated differently. An ethically acceptable development route of GE technology needs to be established in China.

Canada's Assisted Human Reproduction Act: Pragmatic Reforms in Support of Research

Canada's Assisted Human Reproduction Act is long overdue for Parliamentary review. We argue that the current regulation of research using human reproductive materials is not proportionate, not responsive to the uncertain threats posed to human and environmental health and safety, and is not considerate of diverse values in a democratic society. We propose tailored regulatory carve-outs for in vitro research for currently prohibited activities, such as gene editing, and for the exercise of Ministerial Discretion for access by Canadians to experimental in vivo interventions that are currently prohibited, such as mitochondrial replacement therapy. Our recommendations are bounded by constitutional constraints that recognize political and practical challenges in keeping oversight of this research under Federal jurisdiction, whether conducted in academic or private sectors. The proposed nuanced regulatory scheme should be overseen by a new national Agency, modeled on a blend of the Canadian Stem Cell Oversight Committee and Assisted Human Reproduction Canada.

Gene Editing in Clinical Practice: Where are We?

Multitude of gene-altering capabilities in combination with ease of design and low cost have all led to the adoption of the sophisticated and yet simple gene editing system that are clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR). The CRISPR/Cas9 system holds promise for the correction of deleterious mutations by taking advantage of the homology directed repair pathway and by supplying a correction template to the affected patient's cells. CRISPR is a tool that allows researchers to edit genes very precisely, easily and quickly. It does this by harnessing a mechanism that already existed in bacteria. Basically, there's a protein that acts like a scissors and cuts the DNA, and there's an RNA molecule that directs the scissors to any point on the genome one wants which results basically a word processor for genes. An entire gene can be taken out, put one in, or even edit just a single letter within a gene. Several platforms for molecular scissors that enable targeted genome engineering have been developed, including zinc-finger nucleases, transcription activator-like effector nucleases and, most recently, CRISPR/CRISPR-associated-9 (Cas9). The CRISPR/Cas9 system's simplicity, facile engineering and amenability to multiplexing make it the system of choice for many applications. CRISPR/Cas9 has been used to generate disease models to study genetic diseases. Improvements are urgently needed for various aspects of the CRISPR/Cas9 system, including the system's precision, delivery and control over the outcome of the repair process. However, there are still some glitches to be mended like how to regulate gene drives and its safeguards. The creation of gene knockouts is one of the first and most widely used applications of the CRISPR-Cas9 system. Nuclease-active Cas9 creates a double-strand break at the single guide RNA-targeted locus. These breaks can be repaired by homologous recombination, which can be used to introduce new mutations. When the double-strand break is repaired by the error-prone nonhomologous end joining process, indels are introduced which can produce frame shifts and stop codons, leading to functional knockout of the gene. Precedence modification have to be done on mechanism of CRISPR/Cas9, including its biochemical and structural implications incorporating the latest improvements in the CRISPR/Cas9 system, especially Cas9 protein modifications for customization. Current applications, where the versatile CRISPR/Cas9 system is to be used to edit the genome, epigenome, or RNA of various organisms is debated. Although CRISPR/Cas9 allows convenient genome editing accompanied by many benefits, one should not ignore the significant ethical and biosafety concerns that it raises. Conclusively lot of prospective applications and challenges of several promising techniques adapted from CRISPR/Cas9. Is discussed. Although many mechanistic questions remain to be answered and several challenges to be addressed yet, the use of CRISPR-Cas9-based genome technologies will increase our knowledge of disease process and their treatment in near future. Undoubtedly this field is revolutionizing in current era and may open new vistas in the treatment of fatal genetic disease.

Carry on editing

INTRODUCTION OR BACKGROUND

Genome editing facilitates alterations to DNA, large or subtle, in a precise fashion. In its most popular form it uses the programmable endonuclease system, CRISPR/Cas9. Edits can be made to any genome, including the human genome. This raises the possibility of genome editing in human embryos in both a research and reproductive context.

SOURCES OF DATA

All reports of genome editing in human embryos are included here, along with key papers examining the science and ethics of human genome editing.

AREAS OF AGREEMENT

As a basic research tool, genome editing promises to accelerate our understanding of genome biology. It also shows great promise as a means of combatting disease through so-called somatic genome editing.

AREAS OF CONTROVERSY

Genome editing could be used to prevent human disease transmission in a reproductive context. Such germ line interventions are opposed by some, for a number of reasons. Some of these reasons are discussed and a comparison is made with preimplantation genetic diagnosis (PGD).

GROWING POINTS

It is important that scientists, clinicians, bioethicists and other stakeholders engage widely with all those with an interest in genome editing.

AREAS TIMELY FOR DEVELOPING RESEARCH

In addition to offering new insights into human biology, basic (fundamental) research will deliver expertise allowing ever more precise and controllable genome editing methodologies and allied technologies. A range of clear and accessible ethical frameworks must be developed and scrutinized as part of a wider societal debate about possible applications of genome editing. In the UK, human reproductive genome editing can only take place if a change to primary legislation occurs. Inclusive discussions and assessments, involving difficult scientific and ethical concepts, must form part of any democratic decision.

Gene editing in human development: ethical concerns and practical applications

The amazing power of CRISPR-Cas9 gene editing tools and other related technologies has impacted all areas of biology today. It has also raised ethical concerns, particularly with regard to the possibility of generating heritable changes in the human genome - so-called germline gene editing. Although technical and safety issues suggest that this approach is far from clinical application, gene editing as a research tool is moving forward in human embryos, non-human primates and in stem cell-derived embryoids. These studies are already providing new information relevant to our understanding of normal human development, infertility, early pregnancy loss and pluripotent stem cell origins.

Genome editing and assisted reproduction: curing embryos, society or prospective parents?

This paper explores the ethics of introducing genome-editing technologies as a new reproductive option. In particular, it focuses on whether genome editing can be considered a morally valuable alternative to preimplantation genetic diagnosis (PGD). Two arguments against the use of genome editing in reproduction are analysed, namely safety concerns and germline modification. These arguments are then contrasted with arguments in favour of genome editing, in particular with the argument of the child's welfare and the argument of parental reproductive autonomy. In addition to these two arguments, genome editing could be considered as a worthy alternative to PGD as it may not be subjected to some of the moral critiques moved against this technology. Even if these arguments offer sound reasons in favour of introducing genome editing as a new reproductive option, I conclude that these benefits should be balanced against other considerations. More specifically, I maintain that concerns regarding the equality of access to assisted reproduction and the allocation of scarce resources should be addressed prior to the adoption of genome editing as a new reproductive option.

Functional genetics of early human development

Understanding the genetic underpinning of early human development is of great interest not only for basic developmental and stem cell biology but also for regenerative medicine, infertility treatments, and better understanding the causes of congenital disease. Our current knowledge has mainly been generated with the use of laboratory animals, especially the mouse. While human and mouse early development present morphological resemblance, we know that the timing of the events as well as the cellular and genetic mechanisms that control fundamental processes are distinct between the species. The rapid technological development of single-cell sequencing and genome editing together with novel stem cell models of the early human embryo has made it feasible and relevant to perform functional genetic studies directly in human cells and embryos. In this review we will discuss these latest advances where combined transcriptional analysis and genome engineering has begun to shed new insights into the key processes of zygotic genome activation, lineage specification, X-chromosome inactivation and postimplantation development including primordial germ cell specification in the human embryo.

[CRISPR-Cas9, germinal cells and human embryo]

The performance of the molecular tool using CRISPR-Cas9, which makes it possible to induce targeted modifications of the DNA, has found numerous applications in research and open promising prospects in human clinic. CRISPR-Cas9 has been widely used to generate transgenic animals after targeted modification of the genome at the zygotic stage. It was also tested on human embryos on an experimental basis. Although there are potential medical indications that may justify a targeted modification of the embryo or germ cell genome, the uncertainties regarding the efficacy and safety of the method do not allow us to consider implementing such germline gene therapy in the short-term. However, it is necessary to weigh the scientific and ethical issues involved in this approach.