HUMAN EMBRYOS IN THE LAB

 

Scientists' efforts to better understand the early stages of human embryo development in their early stages are yielding results. But this is raising ethical problems that are important.

   When an ovum is fertilized, it will try, according to its possibilities, to develop into a human being. Everything you need is in your genetic information and in your mother's womb. The process is powerful, it is only stopped by situations that the embryo cannot control, and it is very complex. Understanding it is a priority, but limits are reached in which you are playing with a potential human being.

  In 2013 a development biologist looking for a world record, Magdalena Zernicka-Goetz from the University of Cambridge, hoped to get a human embryo cultured the longest in a laboratory. Previous efforts to keep an Scientists' efforts to better understand the early stages of human embryo development in their early stages are yielding results. But this is raising ethical problems that are important. had only lasted about a week. With this, she hoped to get information about the morula, a small mass of cells, and how it transformed into a blastula that already had differentiation in its cells and areas within the embryo that can give rise to different parts of the body already appear.

   Magdalena and her team started with embryos that had been donated by women who no longer needed them for in vitro fertilization procedures. The embryos were bathed in a special culture medium and placed in an incubator, using past experience from their studies in mice.

  The embryos, in the right environment, continued their development, and so they spent a few tense days in which all they could do was see how they continued to grow. The previous record of keeping an embryo alive outside the human body was twelve days, and on that occasion they could go up to thirteen days. That awoke the study of this science that was previously lethargic.

    Researchers' access to the human embryo has always been limited, which has also marginalized knowledge about the study of the first days in the development of a human being. But now, refinements in cell culture methods allow them to grow human embryos outside the body for up to two weeks. Scientists are using gene-editing techniques, such as CRISPR, and are building artificial embryo-like structures to explore the cellular signals and physical forces that shape the embryo and its supporting tissue mold.

   These techniques are illuminating key early processes, such as implantation, when the tiny embryo becomes embedded in the uterine wall and cannot be studied directly. And the new high-resolution digital images reveal in great detail how muscles and nerves grow a few weeks later in development.

   But along with their promise, these new techniques are pushing researchers into unexplored ethical territory. In the early 1970s, ethicists and scientists converged on the '14-day rule', which limits work on human embryos to fifteen days after fertilization, a time when the first signs of nervous system and the last point at which the embryo can divide. Until now, the internationally recognized 14-day rule has been a purely hypothetical limit. But that time frame was not a self-imposed rule, it was the possibility that the embryo outside the body was thought to survive. But now that limit, thanks to new technologies, is moving away.

   Many early developmental processes are strikingly similar throughout the animal kingdom, with each species modifying some genes here or signals there. Among mammals, scientists have studied the mouse more, disabling genes one by one to test what they do. Mice are very similar in the early stages of embryo development, but researchers are beginning to wonder how far these human-mouse similarities go.

   In 2017, his team reported that it used CRISPR-Cas9 to edit a gene expressed in both human and mouse embryonic stem cells. Human embryos with alterations in this gene lacked a protein called OCT4 and were unable to develop into blastocysts, balls of approximately 200 cells. In contrast, mouse embryos lacking the same gene formed blastocysts and failed only later.

   The difference supports the growing idea that even in very early development, some genetic details, such as when certain genes are active, could be human-specific.

   After blooming into a 200-cell ball, the tiny blastocyst must embed itself in the uterine wall to survive. But once this happens (around day seven), scientists cannot study its development.

   Now scientists have made progress. They reported on the first culture systems that could produce human embryos for 12 to 13 days. The researchers demonstrated that with the right cocktail of growth factors and nutrition, cultured human embryos can 'implant' at the bottom of the plate. Surprisingly, the embryos did not require any maternal tissue to trigger the first steps of remodeling that occur after implantation.

   In the latest experiments, after the embryo joined the dish, an outer cell layer began to differentiate into early placenta and other cell types that support embryonic growth. Internally, the cells seemed to develop into precursors to the embryo itself and the yolk sac, an early structure that supplies blood to the embryo. After almost a fortnight, both teams finished the experiments, according to the 14-day rule.

   But some researchers are finding alternative approaches, using human stem cell technology to build synthetic embryo-like structures, which are not covered by the 14-day rule. These constructions lack certain essential components for complete development, and could not give rise to a human being if implanted.    

 

https://www.nature.com/articles/d41586-018-86-z