Gene Editing

The CRISPR gene-edited babies: a technological breakthrough or a brave new future?

He Jiankui announcing the birth of the gene-edited twins on Youtube

He Jiankui announcing the birth of the gene-edited twins on Youtube

The announcement of the first CRISPR gene-edited babies has sparked a major polemic in the scientific community, but also in the media and the public. The research was discreetly carried by a Chinese team lead by He Jiankui at the Southern University of Science and Technology (SUST), in Shenzhen. He announced in a Youtube video: “Two beautiful little Chinese girls, Lulu and Nana, came crying into the world as healthy as any other babies a few weeks ago”. The research team have used CRISPR to deactivate the CCR5 gene in the embryos, which were then implanted into the mother. The CCR5 gene encodes for a protein that enables the HIV virus to enter in human cells. The aim was to deactivate it to reduce the risk of HIV infection, as the father was HIV-positive. This procedure has been apparently applied to eight couples. However, its success is still unclear, as no data or details were publicly released yet.

 

Deletion/insertion in genome by CRISPR Source: Wikimedia

Deletion/insertion in genome by CRISPR Source: Wikimedia

In response to this announcement, many researchers in China and abroad condemned this experiment. Feng Zeng, the pioneer researcher in the application of CRISPR in mammalian cells, called for a global moratorium. Feng insisted that he was “deeply concerned” of the fact that the project was secretly undertaken. More than a 100 Chinese scientists have also signed a letter condemning the experiment. This announcement also coincides with the Second International Summit on Human Genome Editing in Honk Kong, where many researchers reiterated the condemnations against the experiment. It was highlighted by Qiu Renzong (Chinese Academy of Social Science) that this violates the regulation in China, which is however not penalized. In opposition, George Church (Harvard University) defended it saying that HIV was “a major and growing public health threat” and “I think this is justifiable”.

The whole story is not fully known yet, and we still need to wait a few days to have more information to find out how the experiment was conducted. However, this story puts at risk the near future of gene editing, due to the way it was carried, with the secrecy around the project and the non-respect of ethical procedures.

Off-target effects of CRISPR Source: Wikimedia

Off-target effects of CRISPR Source: Wikimedia

At first, the issues with off targets in CRISPR gene-editing means that there are still high risks of inducing unwanted modifications in the genome. So, the babies risk irreversible damage in their genomes, potentially transmitting these to their offspring. Secondly, the way the team carried this experiment creates multiple ethical and practical issues. If the public see that scientists can decide to “engineer babies” in secret without any safety check, we risk to end up banning or restricting CRISPR even more. From an ethical point of view, using CRISPR was not a last resort solution here; other safer options exist to avoid HIV transmission from parents to their children. In practice, the cost of an IVF is not accessible to the vulnerable populations where HIV spreads. The CCR5 gene was probably an “easy” target, giving the opportunity to be the first one in the race to apply CRISPR in humans. But, the attention that this story attracts can negatively impact the public (and policy-makers’) perception of scientists and CRISPR. If the technology lacks a wide public understanding and support, it could delay the release of validated lifesaving treatments for many years.

Even if one day humanity decides to modify itself to prevent diseases, it is still too early and it is not the choice of a single person or a small group of academics. In the end, as scientists, we should do our best to bring life changing solutions, like human gene-editing, in a responsible way to make sure of the best positive impact possible.

“All conditioning aims at that: making people like their unescapable social destiny”

Aldous Huxley, Brave New World


Posted by courtesy of the PLOS Synbio Community blog, where this was originally published.

Written by: Adam Amara

Disclaimer: Views and opinions expressed in EUSynBioS Pulse articles belong solely to the writer(s). They do not reflect the opinion of the Community, the Advisory Board or the Steering Committee.

Extreme makeover yeast edition: de novo synthesis of five chromosomes

Source: Rainis Venta, Creative Commons Attribution-Share Alike 3.0

Source: Rainis Venta, Creative Commons Attribution-Share Alike 3.0

– What I cannot create, I do not understand.

This sentence taken from Richard Feynman’s board at the time of his death essentially captures, if applied to a biological frame, the holy grail of synthetic biology; the understanding of life to such an extent that living systems can be rationally designed to gain and perform specified functions. Synthetic biology is perceived by many as an extension of metabolic engineering, where organisms are modified with end goal to produce a product. This is however part of the story, and the real strength of synthetic biology is the understanding via synthesis, the decomposition of a system to its building blocks and recombination of parts from the bottom up to elucidate the biological complexity.

The construction of a bacterial minimal genome, namely the reduction of the genetic content of Mycoplasma genitalium to 473 genes (1), was hailed as a landmark about a year ago. Last week, a series of seven research articles were published, describing the advancements in the construction of yeast synthetic chromosomes—and as the articles were published in Science, I use this journal’s citation format throughout this blog.

This work is a result of a large consortium, Synthetic Yeast 2.0 , which aims to design and implement a fully synthetic genome of Saccharomyces cerevisiae. The project has existed for several years, and started with the construction of a chromosome’s arms (2), and the first reported synthetic yeast chromosome (3). The recent publications report the synthesis of five more yeast chromosomes, totaling the synthetic sequences to more than one third of the full genome (410). The workflow started from the generation of 700-2000 bp DNA blocks, which are in vitro or in yeast assembled into 10 kb ‘chunks’. A number of chunks are chemically ligated to 30-60 kb ‘megachunks’, which are inserted sequentially into the genome.

Source:  Flickr  CC BY-NC 2.0

Source: Flickr CC BY-NC 2.0

The new chromosomes contain slight modifications from the native ones (4). The tRNA genes were removed from their original loci, and relocated to a specialized neochromosome. Repeating sequences were also removed, the TAG stop codon was replaced with TAA—leaving TAG open for repurposing, such as incorporation of a non-canonical amino acid. The design took place in BioStudio, an open-source computational framework that allows working in genome-scale (4).

Maybe the most important intervention is the inclusion of recombination sites every 10 kb and after every non-essential open reading frame. Consequently, one can implement SCRaMbLE (synthetic chromosome rearrangement and modification by loxP-mediated evolution) and produce numerous strains with rearranged genetic loci, thus acquiring a powerful tool for directed evolution and functional analysis experiments.

What comes next? According to Jeff Boeke, the consortium expects to have a fully synthesized genome by the end of the year (11). However, having obtained all synthetic chromosomes does not automatically mean that a fully ‘synthetic’ yeast strain will become immediately available;  although strains incorporating one heterologous chromosome do not display a particular phenotype, a strain with three of its chromosomes replaced had a growth defect (5). Issues arising from chromosome interactions and telomere function already show, while more unknown challenges are sure to appear.

The long-term goal of this colossal undertaking is to allow research labs and organizations to routinely use custom-made organisms. This dream seems to come closer and closer, but I do not think it will happen within the next few years. The cost for synthesizing the whole S. cerevisiae genome is estimated to 1-1.5 M dollars, without taking into account salaries and maintenance (4).  But I believe that the scientific insights obtained by this project will affect synthetic biology in multiple ways. And then, why not expand to more organisms? The recent proposal to synthesize a human genome gained a lot of publicity (and controversy).  A minimal or synthetic plant genome [see Marchantia polymorpha, a small liverwort (12), and Physcomitrella patens, a moss where homologous recombination happens with the same efficiency as in yeast (13)] will be leap forwards in understanding and harnessing photosynthesis…

Disclaimer: This post originally appeared at PLOS synbio (link) and is reproduced with permision

References

  1.    C. A. Hutchison et al., Design and synthesis of a minimal bacterial genome. Science. 351, 6253–6253 (2016).
  2.     J. S. Dymond et al., Synthetic chromosome arms function in yeast and generate phenotypic diversity by design. Nature. 477, 471–476 (2011).
  3.     N. Annaluru et al., Total Synthesis of a Functional Designer Eukaryotic Chromosome. Science. 344, 55–58 (2014).
  4.     S. M. Richardson et al., Design of a synthetic yeast genome. Science. 355, 1040–1044 (2017).
  5.     L. A. Mitchell et al., Synthesis, debugging, and effects of synthetic chromosome consolidation: synVI and beyond. Science. 355 (2017), doi:10.1126/science.aaf4831.
  6.     G. Mercy et al., 3D organization of synthetic and scrambled chromosomes. Science. 355 (2017), doi:10.1126/science.aaf4597.
  7.     Y. Wu et al., Bug mapping and fitness testing of chemically synthesized chromosome X. Science. 355 (2017), doi:10.1126/science.aaf4706.
  8.     W. Zhang et al., Engineering the ribosomal DNA in a megabase synthetic chromosome. Science. 355 (2017), doi:10.1126/science.aaf3981.
  9.     Y. Shen et al., Deep functional analysis of synII, a 770-kilobase synthetic yeast chromosome. Science. 355 (2017), doi:10.1126/science.aaf4791.
  10.   Z.-X. Xie et al., “Perfect” designer chromosome V and behavior of a ring derivative. Science. 355 (2017), doi:10.1126/science.aaf4704.
  11.   A. Maxmen, Synthetic yeast chromosomes help probe mysteries of evolution. Nature (2017), doi:10.1038/nature.2017.21615.
  12.   C. R. Boehm, B. Pollak, N. Purswani, N. Patron, J. Haseloff, Synthetic Botany. Cold Spring Harb. Perspect. Biol., a023887 (2017).
  13.   B. C. King et al., In vivo assembly of DNA-fragments in the moss, Physcomitrella patens. Sci. Rep. 6, 25030 (2016).