In the earliest stages of human embryonic development, a small collection of cells known as human embryonic stem cells (hESCs) orchestrates growth and differentiation, eventually leading to highly specialized human tissues. B. Pluripotent Cells -; Precursors of all cell types in the body -; hESCs are of central interest to developmental and regenerative biologists. Many genes that drive hESC function have already been identified, but powerful tools that shed light on the interrelated activities of these genes have only recently emerged.

Researchers at Brigham and Women’s Hospital and Harvard Medical School used genome-wide genetic screening to both overexpress and inactivate (“knock out”) tens of thousands of genes in hESCs. They uncovered key networks that simultaneously control pluripotency and readiness for cell death (apoptosis), thus helping to ensure optimal conditions for embryonic development. The results of the study, published in Genes and Development, offer new insights into cancer genetics and a new approach to research in regenerative medicine.

Our methods enabled us to “atlas” almost every gene in the human genome and determine what its overexpression or loss means in the most basic early stages of human development. Instead of looking at genes individually, we examined thousands of genetic changes simultaneously to find out how they affect the reproduction of embryonic stem cells and then the development of the three cotyledons, which are the starting materials for human tissues. “

Kamila Naxerova, PhD, first author, former postdoctoral fellow in the Elledge Laboratory, Brigham’s Division of Genetics

“Understanding the genetic control of human embryonic stem cell function is essential to our understanding of developmental biology and regenerative medicine,” said co-author Stephen Elledge, PhD, Gregor Mendel Professor of Genetics and Medicine at Brigham and HMS. “Our study provides the most comprehensive examination of gene functionality in hESCs to date.”

When conducting their experiment -; that involved knocking out about 18,000 genes and overexpressing 12,000 genes -; The researchers found that hESC genes play a unique role controlling pluripotency, or differentiation capacities. When the researchers deleted these known genes, including OCT4 and SOX2, the stem cells surprisingly increased their resistance to death, suggesting that, under normal circumstances, pluripotency regulators also contribute to apoptotic pathways. The researchers hypothesized that the genetic link between pluripotency and strictly regulated cell death helps destroy a damaged stem cell early in embryonic development before it can affect the function of future cells and tissues.

These interrelated behaviors were particularly evident in a pluripotency regulator known as the SAGA complex. The researchers showed for the first time that hESCs die less easily in the absence of the SAGA complex. In addition, its absence inhibited the development of all three cotyledons (endoderm, mesoderm, and ectoderm), demonstrating the central role of the SAGA complex in a number of hESC activities. Finally, the researchers observed that many of the genes that regulate the formation of the three cotyledons are also known to contribute to cancer growth when they are over- or under-expressed in body cells.

The study’s high-throughput genetic screening approach not only offers a new perspective on the genetic basis of cancers, but can also influence future work in regenerative biology.

“Genetic screens provide a wonderful opportunity to examine how genetic networks contribute to interconnected cellular behaviors such as growth, differentiation, and survival,” said Naxerova, who is now an assistant professor at the Center for Systems Biology at Massachusetts General Hospital. “This approach can help regenerative and developmental biologists systematically map genetic networks involved in the formation of certain tissues and manipulate these genes to grow different types of human tissue from stem cells more efficiently.”


Brigham and Women’s Hospital

Journal reference:

Naxerova, K., et al. (2021) Integrated loss of function and gain of function screens define a core network that controls the behavior of human embryonic stem cells. Genes & Development.


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