Until a few hundred years ago, before scientific advances allowed researchers to peer inside the human body or extract cells to study them in the laboratory, I imagine that the mysteries of developmental biology—more than any other discipline—must have stumped humans. On one hand, one could visibly track a baby’s growth based on the size of the mother's growing bump; if everything went right, a healthy baby would emerge after nine months. On the other hand, sometimes a seemingly healthy mother lost her child mid-pregnancy or delivered an abnormal newborn. In the absence of scientific technologies to probe into the womb, the inner workings of embryonic development remained a black box and people had little to no way of knowing what to expect when someone was expecting.
While several questions remain unanswered even today, scientists rapidly bridged most of the knowledge gaps once stem cell research entered the scene. You might recall that in our winter issue last year we covered how researchers used adult stem cells to better understand placental development. In one of the articles in this issue, we profile a biologist with expertise in endometrial research who found that stem cells were a powerful tool for solving long-standing mysteries about women's health.
While access to adult stem cells has certainly helped answer some questions in developmental biology, embryonic stem cell studies, in my opinion, truly transformed the research area. Just like the newborn that the embryo eventually forms into, these early-stage cells have the potential to choose any path of maturation. By developing 3D embryonic stem cell models, researchers study the differentiation and growth of these cells without worrying about the restrictive rules on embryo research (read more about these advances in one of the feature stories in this issue). What also fascinates me is that researchers can now achieve single cell resolution in their quest to determine how life develops early on; one research team recently found that the initial two cells in an embryo take diverse developmental paths.1 These studies are a stark reminder that scientists have indeed come a long way from not knowing what happens during the months-long gestation period to following the development of two individual cells to determine their eventual contribution to structure and function!
In contrast to the early embryonic development studies inspired by visible signs, it must have been hard in those days to imagine problems within an individual’s brain when their symptoms did not match known physical disorders. Securing neurons from the brain is also not as easy as isolating most other cell types. It is no secret that the ability to transform normal cells into induced pluripotent stem cells revolutionized neuroscience, as researchers finally found a way to model brain disorders in these cells. Now with more knowledge about how sex affects disease, researchers are correcting the long-standing sex bias in the field to further refine our understanding of the human brain. For those interested in reading more about this topic, we dive into the measures that researchers are taking to include sex as a biological variable in their studies in a feature article in this issue.
All in all, the applications of stem cells are as diverse as the cells’ differentiation abilities, and researchers have only scratched the surface so far. I hope you experience the same enthusiasm and excitement reading the stem cell stories in this issue that we had while crafting them.
- Junyent S, et al. The first two blastomeres contribute unequally to the human embryo. Cell. 2024;187(11):2838-2854.
