| Comments |
P.5 left column: "Furthermore, [investigators'] estimates of numbers of expressed genes/transcripts and mRNA message content per cell (519,688 to 851,087 mRNAs per cell, 8,357 to 12,739 transcripts, expressed from 8,101 to 11,360 genes, Table 4) compare well with previous estimates ranging from 200,000 to 600,000 mRNAs per cell [refs 20, 21], consisting of 11,500 to 15,000 diverse mRNA species [refs 18, 20], transcribed from as many or more genes up to 17,000 [refs 18, 20, 22]. Second, a majority of transcripts expressed in one tissue or cell type are commonly expressed in other diverse cell and tissue types. The number of expressed genes in each tissue was estimated by counting the number of microarray features measuring absolute expression of at least one copy per cell, and converting this set of microarray probes to U-clusters (loci) and transcripts via the NIA [National Institute on Aging] Mouse Gene Index (Table 4). Examination of the overlap between each cell type's roster of expressed genes and transcripts reveals that the majority are expressed in common (Tables 4 and 5), as suggested by previous assessments of mRNA complexity [refs 18, 20, 22]. For example, 93% of expressed placental transcripts are also expressed in embryo, and this group represents 72% of the expressed transcripts in embryo (Table 5). The same relationship holds true for pairings of cultured cells with embryo, with 95% of expressed transcripts in cultured cells also found in embryo, covering 69% of embryonic transcripts." EM = whole embryo, PL = placenta, ES = embryonic stem cells, TS = trophoblast stem cells |