![]() Although these rearrangements can result in the exchange of alleles between chromosomes, the order of the genes on the interacting chromosomes typically remains the same. Perhaps someday, Feschotte says, monitoring levels of LINE-1 expression in embryos growing in fertility clinics may help explain very early losses at the implantation stage.In general recombination, DNA rearrangements occur between DNA segments that are very similar in sequence. Identifying potential causes of embryonic cell damage also expands our understanding of early pregnancy. Singh says the ability to pick out pluripotent cells from REject cells within the early embryo will be indispensable for researchers studying regenerative medicine, who need to be able to grow different types of body tissues in order to create laboratory models of diseases. With the introduction of synthetic embryos, three-dimensional balls of cells derived from stem cells rather than from sperm and eggs, Feschotte thinks scientists may be able to answer some of these lingering questions. Since these embryos are observed outside the parent’s body, researchers “can’t quite rule out that some of the results are an artifact of in vitro culture,” says Feschotte. ![]() Many regions don’t allow it, and in those that do, researchers rely on leftover embryos, frozen at roughly five days old, donated by parents after they’ve had a successful IVF cycle. Ware adds that it is also unknown whether REjects are merely garbage, or whether they serve a functional, albeit brief, role in the developing embryo.Įmbryonic stem cell research is also hard to do because it’s ethically fraught. While LINE-1 and HERVH expression appeared mutually exclusive-REjects expressed LINE-1 and not HERVH, and vice versa for surviving cells-these researchers had no way to find direct evidence that HERVH controls LINE-1, says Cedric Feschotte, a molecular biology and genetics professor at Cornell University who was not involved in this study. But drawing strong conclusions about embryonic development in the womb based on a lab study is tricky. These findings are “remarkable,” says Ware. Singh suspects that because the placenta only sticks around for nine months, rather than a whole lifetime, its cells don’t last long enough for DNA damage to matter. LINE-1 is active within these cells too, but unlike REjects, they don’t die. The five-day-old embryo is surrounded by an outer layer of cells that will soon become the placenta. “These retroviruses had invaded to kill the system, and now they are working to protect the system against other retroviruses.” “It’s kind of a romantic relationship,” says Singh. Despite being another ancient invader, HERVH actually suppresses LINE-1, shielding the pluripotent cells from harm and ensuring that they can continue to divide. But the surviving cells express something that the REjects do not: HERVH. On the embryo’s fifth day after fertilization, Singh’s team found, the self-destructing REjects still exist alongside the healthy cells they will sacrifice themselves to protect. Singh’s team dubbed these damaged cells “REjects,” a nod to their cause of death: RE for “retroelements” like LINE-1, “rejected” from the growing embryo. This damage, Singh suspected, was LINE-1’s calling card. Instead, the cells had the signatures of DNA damage and precursors to apoptosis, a controlled mechanism that the body uses to cull stressed or damaged cells. Most were clustered according to genetic markers that determine their fate within the growing embryo-for example, if they will become part of the ectoderm, the precursor to skin and brain cells, or the endoderm, which evolves into respiratory and digestive tissues.īut one cluster did not seem marked for any kind of future. He ran an analysis that grouped cells based on the similarity of their gene expression. Today only one family of transposable elements remains active in humans: long interspersed nuclear elements, or LINE-1. Most of these mobile sequences, called transposable elements, have since lost their jumping abilities, tamed by evolution. ![]() Nearly 40 percent of our modern genetic material comes from ancient retroviruses, all of which were once capable of “jumping” into parts of the genome where they didn’t belong. ![]() “It’s a classical example of fighting fire with fire.” “I think of it as two dragons, one from the side of death, one from the side of the living,” says Singh, an assistant professor at the Max-Planck Institute for Multidisciplinary Sciences in Gottingen, Germany. Without HERVH as a bodyguard, other cells are more vulnerable to DNA damage-and once they’re overwhelmed, they sacrifice themselves to spare the developing fetus. Cells in which HERVH is activated can suppress the attack of damage-causing sequences. The survivors are protected by the assimilated remains of another ancient retrovirus: a gene sequence called HERVH.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |