Scientists Grow Primate Embryos in Vitro for Record 25 Days, Advancing Understanding of Organ Development

Zoom in / Computer-generated image of an early stage of embryonic development, before organ formation begins.

Scientists set a new record for growing primate embryos outside the womb, as reported in the May issue of the journal Cell. For the first time, monkey embryos were cultured in vitro 25 days after fertilization, achieving key developmental milestones not previously observed in culture, including the onset of organ development. Being able to track these processes in the laboratory may be an important step toward understanding birth defects and organ development in humans.

Understanding development

The early stages of an animal’s development, often referred to as embryonic development, involves the transition from a seemingly unremarkable mass of cells to a complex, fragmented organism. At the conclusion of embryogenesis, cells begin to proceed towards specialization, and organ systems begin to form. In mammals, this process typically occurs in the comfort and privacy of the uterus, making it difficult to observe, even with the advent of advanced imaging. It is difficult to experiment with factors that may affect development.

All of this led evolutionary biologists to look for ways to make this process happen in a culture dish, bypassing these limitations. The study of human embryonic development is restricted by ethical and legal considerations. While specific guidelines may vary from country to country, the result is an almost universal ban on human embryos preserved in the lab after 14 days — before the nervous system’s progenitors have formed. This detail is of particular medical importance, as irregularities during formation of the nervous system can lead to a range of conditions affecting the spine, spinal cord, and brain, including spina bifida.

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Most of our understanding of this process comes from studies of mouse and chicken embryos.

But even a mouse is more than a hop, skip, and hop away from humans on the Tree of Life; While we are remarkably similar in some ways, there are notable differences in the timing of development, genetic activity, and even the physical arrangement of the fetus is different.

Five more days

Two independent groups of researchers, publishing papers back-to-back, have attempted to fill this gap by developing a major system for the study of embryonic development. Use of fertilized embryos of macaques (macaca filling), Both groups were able to culture primate embryos for 25 days after fertilization. This exceeds the previous record of 20 days, allowing researchers to view more advanced stages in organ development.

Each group developed a distinct style, but both were able to obtain embryos very similar to each other. in the womb counterparts ever. One of the keys to achieving this was to promote the three-dimensional development of the fetus. Previous efforts relied on 2D culture conditions, which were plagued by excessive tissue growth and eventual embryo collapse by day 20. To address this, the team led by Hongmei Wang optimized culture conditions in a liquid suspension, while Tao Tan’s group used mechanical supports. . Both approaches seem to facilitate proper 3D growth.

The survival rate of fetuses to day 25 ranged from approximately 20 to 40 percent, depending on the study and the measures used. This may not exactly be an efficient, high-yield success, but it is a huge improvement over previous technologies. Importantly, embryos that survived up to 25 days had many of the hallmarks of in the womb Embryo, such as the three layers of embryonic tissue ultimately responsible for creating the embryo (the endoderm or lining of the intestine, the ectoderm which forms the skin and nerves, and the mesoderm, which is everything else). The researchers also documented evidence of further organogenesis and the formation of the neural tube, which goes on to form the brain and spinal cord.

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All of this constitutes a very promising step towards a traceable system for studying the formation of the primary embryo, but the techniques are far from perfect. Currently, fetuses do not survive beyond 25 days in any of the group of cases. However, both groups have suggested that an improved combination of growth and signaling molecules, combined with more advanced mechanical scaffolding, may better mimic conditions in utero and preserve embryos at later stages of development.

cell، 2023. DOIs: 10.1016 / j.cell.2023.04.019And 10.1016 / j.cell.2023.04.020

Lita Kacsoh holds a master’s degree in public health from Emory University and a doctorate in molecular biology from Dartmouth Medical School. When she’s not writing, you’ll likely find her reading or drinking coffee.

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