Accession Numbers
The Gene Expression Omnibus (GEO) (http://www.ncbi.nlm.nih.gov/geo) accession number for all raw microarray data used in this study is GSE2248.
The Unigene (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=unigene) accession numbers for the gene products discussed in this paper are aggrecan (Hs.2159 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=2159; bone sialoprotein (Hs.518726 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=518726; bone-specific alkaline phosphatase (Hs.75431 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=75431; collagen II (Hs.408182 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=408182; forkhead box D1 (Hs.519385 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=519385; hepatocyte growth factor (Hs.396530 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=396530; mesenchymal stem cell protein (DSC54, Hs.157461 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=157461; MyoD (Hs.520119 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=520119; myogenin (Hs.2830 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=2830; myosin heavy chain IIa (Hs.513941 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=513941; Nanog (Hs.329296 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=329296]) [15]; neuropilin 1 (Hs.131704 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=131704; notch homolog 2 (Hs.549056 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=549056; Oct-4 (Hs.504658 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=504658; and PPARγ (Hs.162646 [http://www.ncbi.nlm.nih.gov/UniGene/clust.cgi?ORG=Hs&CID=162646]).
Patient Summary

Background
The discovery and isolation of human embryonic stem cells (cells that are capable of renewing themselves and turning into the many different cell types that make up the human body) has the potential to revolutionize the treatment of many diseases that require the replacement of abnormal or missing cells. In particular, it would be very valuable to be able to replace tissues that are derived from one particular tissue type—mesenchyme—which bone, cartilage, fat and muscle develop from. However, before such treatments can happen, it will be necessary to work out exactly how embryonic cells become other cells, and whether it is possible to make these changes happen in the laboratory.

What Did the Researchers Do?
They took two lines of completely undifferentiated human embryonic stem cells and by culturing them in the presence of mouse cells stimulated them to turn into mesenchymal cells. They then treated these cells with compounds to make them change into specialized bone, cartilage, fat, and muscle cells. They were able to confirm that these cells were all human (important because the early part of the experiment is done in the presence of mouse cells) and also that there was no evidence that the cells became cancerous.

What Do These Findings Mean?
It is theoretically possible to produce lines of bone, cartilage, fat, and muscle cells from human embryonic stem cells. However, the process will need more refinement before the cell lines could be used for treatment; ideally, for example, all the culturing would be done without any mouse cells.

Where Can I Get More Information?
The United States National Institutes of Health has a group of Web pages on stem cells: http://stemcells.nih.gov/info/faqs.asp 
The International Society for Stem Cell Research has a list of frequently asked questions about stem cells: http://www.isscr.org/science/faq.htm