In a significant scientific achievement, researchers have managed to cultivate monkey embryos in a laboratory environment long enough to witness the early stages of organ formation and nervous system development. These critical milestones, which are challenging to observe in utero, were reached by the embryos, making them potentially the oldest primate embryos to be grown outside the womb. The findings were separately reported by independent teams in two papers published in Cell on May 11.

Lab-grown embryos typically struggle to survive beyond a few weeks, often resulting in an assortment of cells in a dish without any significant progress. Previously, both research teams had successfully cultured monkey blastocysts (clusters of dividing cells) in Petri dishes for up to 20 days. However, further development beyond that point was impeded, preventing the observation of advanced stages such as early signs of organ formation and the nervous system.

In the new studies, the scientists employed small vials of culture medium, allowing the embryos to grow in three dimensions, similar to their natural development inside the womb. By employing this technique, both teams managed to sustain their embryos for 25 days after fertilization, surpassing previous limitations. To the knowledge of both the authors and external experts consulted, no older primate embryos have been grown in a lab.

The team led by Hongmei Wang from the Chinese Academy of Sciences collected egg cells from female cynomolgus monkeys and fertilized them with sperm from their male counterparts. The resulting blastocysts were then placed in a gel-like substance within small cylindrical containers and observed for 25 days. Around two weeks after fertilization, over half of the embryos exhibited an embryonic disk—a flat mass of cells—which later developed into the three primary cell layers of the body: endoderm, mesoderm, and ectoderm. The lab-grown embryos also exhibited genetic features similar to those seen in natural monkey embryos within the same time frame. By day 20, the embryos had formed a neural plate, a key indicator of early nervous system development. The researchers also identified cells that would eventually become motor neurons, providing valuable insights into primate embryo development.

In the second study, led by Tao Tan from Kunming University of Science and Technology, blastocysts were generated from cynomolgus monkey eggs and sperm. The team utilized two different types of cell culture to provide stronger mechanical support and supplemented with glucose to enhance energy supply during growth. The cultured embryos showed similarities to natural embryos between 18 and 25 days after fertilization. Further analysis revealed differentiation of mesoderm cells into heart muscle cells, blood and lymphatic vessel lining cells, connective tissue cells, and the foundational cells of the digestive system. The researchers also observed the early formation of blood cells and components in the yolk sac, a structure that nourishes the embryos.

Experts lauded the studies as a significant advancement in sustaining embryos outside the womb for longer periods. However, they caution that more progress is necessary before lab-grown embryos can fully resemble their natural counterparts. While the embryos in the studies demonstrated some differences from expected development at these stages, the breakthrough paves the way for future improvements and a deeper understanding of primate embryonic development.

By Impact Lab