Whitehead researchers have developed a new type of genetic2 screen for human cells to pinpoint3 specific genes4 and proteins used by pathogens(病原体), according to their paper in Science. In most human cell cultures genes are present in two copies: one inherited from the father and one from the mother. Gene1 inactivation5(钝化作用) by mutation6 is therefore inefficient7 because when one copy is inactivated8, the second copy usually remains9 active and takes over.
In yeast10(酵母), researchers have it easier: they use yeast cells in which all genes are present in only one copy (haploid单倍体 yeast). Now Carette and co-workers have used a similar approach and used a human cell line, in which nearly all human chromosomes11 are present in a single copy.
In this rare cell line, Carette and co-workers generated mutations in almost all human genes and used this collection to screen for the host genes used by pathogens. By exposing those cells to influenza12(流感) or to various bacterial13 toxins15(毒素), the authors isolated16 mutants that were resistant17 to them. Carette then identified the mutated genes in the surviving cells, which code for a transporter molecule18 and an enzyme19(酶) that the influenza virus hijacks20 to take over cells.
Working with Carla Guimaraes from Whitehead Member Hidde Ploegh's lab, Carette subjected knockout cells to several bacterial toxins to identify resistant cells and therefore the genes responsible.
The experiments identified a previously21 uncharacterized gene as essential for intoxication22 by diphtheria toxin14(白喉毒素) and exotoxin(外毒素) A toxicity23, and a cell surface protein needed for cytolethal distending24 toxin toxicity.
"We were surprised by the clarity of the results," says Jan Carette, a postdoctoral(博士后的) researcher in the Brummelkamp lab and first author on the Science article. "They allowed us to identify new genes and proteins involved in infectious processes that have been studied for decades, like diphtheria and the flu. In addition we found the first human genes essential for host-pathogen interactions where few details are known, as is the case for cytolethal distending toxin secreted25 by certain strains of E. coli(大肠杆菌). This could be important for rapidly responding to newly emerging pathogens or to study pathogen biology that has been difficult to study experimentally."
Brummelkamp sees the work as only the beginning.
"Having knockout cells for almost all human genes in our freezer opens up a wealth of biological questions that we can look at," he says. "In addition to many aspects of cell biology that can be studied, knockout screens could also be used to unravel26 molecular27 networks that are exploited by a battery of different viruses and bacteria."