="text-align: center;">Scientists Generate “Essentialome” with the Help of CRISPR Screening
Haploid cells allow genetic screening through the generation of a highly enriched hemizygous mutant library, owing to the single set of chromosomes in these cells. Much previous work on haploid genetics has been carried out in unicellular organisms, but recent developments have made it possible to extend this field into mammalian cells.
Now, however, scientists at the Hebrew University of Jerusalem isolated haploid human embryonic stem cells and performed a genome-wide CRISPR–Cas9-based loss-of-function screen on karyotypically normal haploid hPSCs to define the genes essential for normal growth and survival of human PSCs and the genes that restrict their growth.
“Our screen revealed the essence of hPSC-specific genes and marked the major pathways that regulate the growth of these cells,” the scientists wrote in its published paper in Nature Cell Biology. The results also revealed opposing roles for tumor suppressors and oncogenes, evaluated the role of genes for hereditary diseases in early development and growth in humans and showed how carcinogenic genes could affect the growth of the human embryo.
“This study creates a new framework for understanding what it means to be an embryonic stem cell on it genetic level, “says co-author Atilgan Yilmaz, Ph.D. “The more complete a picture we have of nature in these cells, the better chances we have for successful therapies in the clinic.”
The researchers analyzed virtually all human genes in the human genome by generating more than 180,000 distinct mutations. To produce such a vast array of mutations, they combined a sophisticated gene-editing technology (CRISPR-Cas9 screening) with a new type of embryonic stem cells that was recently isolated by the same research group.
This new type of stem cells harbors only a single copy of the human genome, instead of two copies from the mother and father, making gene editing easier thanks to the need of mutating only one copy for each gene.
The study found that a mere 9% of all the genes in the human genome are essential for the growth and survival of human embryonic stem cells, whereas 5% of them actually limit the growth of these cells.
The team could also analyze the role of genes responsible for all hereditary disorders in early human development and growth. Furthermore, they showed how cancer-causing genes could affect the growth of the human embryo.
“This gene atlas enables a new functional view on how we study the human genome and provides a tool that will change the fashion by which we analyze and treat cancer and genetic disorders,” said Prof. Nissim Benvenisty, MD, PhD, Director of the Azrieli Center for Stem Cells and Genetic Research and the Herbert Cohn Chair in Cancer Research at the Hebrew University of Jerusalem, and the senior author of the study.
Another key finding of the study was the identification of a small group of genes that are uniquely essential for the survival of human embryonic stem cells but not to other cell types. These genes are thought to maintain the identity of embryonic stem cells and prevent them from becoming cancerous or turning into adult cell types.
