A collage of human embryonic stem cell images
© Paul Gokhale, University of Sheffield, UK
Human embryonic stem cells (ESCs) represent a uniquely valuable tool for developmental biology and a promising resource for regenerative medicine. To maximize their utility, scientists from around the world gathered together in 2005 to form the International Stem Cell Initiative (ISCI), a group dedicated to establishing optimized strategies for ESC research.
Most recently, the ISCI investigated the extent to which ESC lines acquire genetic changes after extended periods of culture, a problem that could potentially render these cells unusable by predisposing them to cancerous growth. “With human pluripotent cells moving towards clinical applications, it was essential to determine if mutations arise in culture — mutations that one would not want delivered into future patients,” says Paul Robson at the A*STAR Genome Institute of Singapore, who participated in the study.
Robson joined with Barbara Knowles of the A*STAR Institute of Medical Biology and 120 other colleagues from around the world to examine 125 human ESC lines, representing a broad variety of ethnicities and geographic regions. The researchers looked for changes in either the number of chromosomes or in the structure of individual chromosomes, examining each line in the initial stages of cell culture (early passage) or after protracted cultivation and many rounds of cell division (late passage).
Most of the cell lines showed overall genomic stability, with no major changes between early and late passage. A few specific chromosomal regions were repeatedly affected in instances of structural rearrangement. Most notable was the duplication of 20q11.21 — a small, specific region of chromosome 20 that occurred in 22 different cell lines. This change appeared in later passages, and seems to establish a growth advantage by removing regulatory barriers to cell division. “This re-occurring 20q11.21 amplification is also found in several types of cancer,” says Robson.
The ISCI team also identified abnormalities in chromosomes 1, 12 and 17, echoing previous reports of such genomic alterations. However, they were unable to zero in on specific genes that might make these changes advantageous for cell growth. Without more data, this question is likely to remain open for the time being.
Last but not least, the group identified a candidate gene in the 20q11.21 region, called BCL2L1, which encodes a protein that contributes to cell survival and proliferation. There are many other genes within this region, and Knowles and Robson are now collaborating to delve deeper. “We are following up on characterizing the genes within the 20q11.21 region to determine which of them may be functionally responsible for promoting cell growth and by what mechanism,” says Knowles.
The A*STAR-affiliated researchers contributing to this research are from the Genome Institute of Singapore, the Institute of Medical Biology, the Bioprocessing Technology Institute and the Singapore Stem Cell Consortium.
