Keeping The Reserve Force Home

Hematopoietic stem cells—bone marrow-derived adult stem cells that give rise to the wide variety of specialized blood cells—come in two flavors: the reserve force that sits quietly waiting to be called upon and the active arm that continually prolifeates, spawning billions of blood cells every day. In their latest study, Stowers Investigator Linheng Li, PHD and his team revealed that genomic imprinting, a process that specifically shuts down one of the two gene copies found in each mammalian cell, prevents the reservists from being called up prematurely.

Sexual reproduction yields progeny with two copies, or alleles, for each gene, one from the mother and one from the father. Most genes are expressed from both copies, but in mammals and marsupials a small subset of genes receives a mark, or imprint during the development of egg or sperm cells. These genomic imprints not only differentiate between genes of maternal and paternal origin, but they specifically shut down one copy of those genes in the offspring.

“Active HSCs (hematopoietic stem cells) form the daily supply line that continually replenishes worn-out blood and immune cells while the reserve pool serves as a backup system that replaces damaged active HSCs and steps in during times of increased need,” explains Li. “In order to maintain a long-term strategic reserve of hematopoietic stem cells that lasts a lifetime, it is very important to ensure that the backup crew isn’t mobilized all at once. Genomic imprinting provides an additional layer of regulation that does just that.”

The study was published in the August 15, 2013, issue of the journal Nature.