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Comparative proteomics study suggests germ-cell-derived stem cells can stand in for ESCs
Most of the proteins cataloged in the study are annotated as intracellular, with 38% localized to the nucleus. The proteins are implicated in such functions as The past few years may have been lean protein synthesis, cell differentiation, for U.S. scientists interested in human RNA metabolism, and managing oxidaembryonic stem cells (ESCs), but at tive stresssthus, primarily housekeeping least their research wasn’t illegal. In genes. One protein, Trim28, was recently Germany, work on human ESCs isoimplicated as a marker of pluripotency, lated after May 2007 is banned. says Dihazi. Naturally, researchers have been Because 2DE favors the searching for work-arounds, most abundant proteins in and in 2006, they found a proteome, Heazlewood two. One was the discovery suggests that a far deeper by Shinya Yamanaka of catalog could be obtained Kyoto University that soby replacing 2DE with 2Dmatic cells can be genetiLC/MS/MS and quantitative cally “reset”, via the introtechniques such as stableduction of genes encoding isotope labeling by amino four transcription factors, acids in cell culture (SILAC). into ESC-like induced pluriSuch an approach, Krijgspotent stem cells. The other veld adds, would also prowas the observation by vide data on proteome dyWolfgang Engel and Gerd namics, whereas the current Hasenfuss of the University study examined a static of Go¨ttingen (Germany) snapshot. that adult mouse sperPattern matching. 2D-DIGE of paired ESC and maGSC samples illustrates But Dihazi says it would matogonial stem cells their apparent similarity. be difficult to make the (SSCs) could be induced in kinds of comparisons his culture to adopt ESC-like team made with LC approaches. “2DE is backgrounds. They found that 96% of propertiessthat is, they can form cells not the newest method,” he says, “but it the identified proteins were identical; from all three “germ layers” of the body: is still one of the best methods to get an just 18 identified proteins differed in endoderm, ectoderm, and mesoderm. overview of a cell line or tissue.” abundance between maGSCs and ESCs. Engel and co-workers subsequently Laurence M. Brill, a senior scientist When they tried to validate those differdemonstrated that these pluripotent at the Burnham Institute for Medical ences via western blotting in two addiSSCs, which they dubbed “multipotent Research in La Jolla, Calif., says the tional matched maGSC and ESC pairs, adult germline stem cells” (maGSCs), data are consistent with the conclusion however, they failed to reproduce the expressed microRNA profiles akin to that the two cell types are comparable, findings, suggesting the differences are those of ESCs. Now, in a recent JPR but he notes that much deeper proartifacts of genetic background, as oppaper (2009, DOI 10.1021/pr900565b), teome coverage and follow-up biologiposed to fundamental differences behis team, in collaboration with that of cal studies are needed to strengthen tween the two cell types. Hassan Dihazi, demonstrates the apthe initial findings and probe the poThe conclusion, Dihazi says, is that parent similarity between maGSCs and tential roles of the identified proteins maGSCs and ESCs are essentially indisESCs at the proteome level. in pluripotency. tinguishable at the proteome level, a “We wanted to give an overview of Engel, Dihazi, and their teams are finding that supports the use of the proteome of SSCs and to compare already working on that. They are maGSCs as alternatives to ESCs. the proteome to ESCs to prove they are combing through the data, looking for Joshua Heazlewood, the director of more or less identical and thus can be potential pluripotency markers. One of systems biology at Lawrence Berkeley used as an alternative to ESCs,” Dihazi their ultimate goals, and that of the National Laboratory, calls that concluexplains. university’s nephrology department, is sion “a fairly bold call.” He notes that Dihazi and his colleagues developed to differentiate maGSCs into kidney Dihazi and his colleagues identified
