The transcriptional diversity of 25 Drosophila cell lines

Drosophila melanogaster cell lines are important resources for cell biologists. Here, we catalog the expression of exons, genes, and unannotated transcriptional signals for 25 lines. Unannotated transcription is substantial (typically 19% of euchro- matic signal). Conservatively, we identify 1405 novel transcribed regions; 684 of these appear to be new exons of neighboring, oftendistant, genes. Sixty-four percent of genes areexpressed detectably in atleastone line, but only 21%are detected in all lines. Each cell line expresses, on average, 5885 genes, including a common set of 3109. Expression levels vary over several orders of magnitude. Major signaling pathways are well represented: most differentiation pathways are ''off'' andsurvival/growth pathways''on.''Roughly 50%ofthe genesexpressed by eachlinearenot part ofthe commonset, and these show considerable individuality. Thirty-one percent are expressed at a higher level in at least one cell line than in any single developmental stage, suggesting that each line is enriched for genes characteristic of small sets of cells. Most re- markable is that imaginal disc-derived lines can generally be assigned, on the basis of expression, to small territories within developing discs. These mappings reveal unexpected stability of even fine-grained spatial determination. No two cell lines show identical transcription factor expression. We conclude that each line has retained features of an individual founder cell superimposed on a common ''cell line'' gene expression pattern. (Supplemental material is available for this article. The data from this study have been submitted to the NCBI Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo) under accession nos. GSE15596, GSE16269-GSE16290, GSE16321- GSE16322, GSE16325, and GSE18040. All of the microarray data, RNA-seq data, and expression scores for genes and exons are available from the Data Coordination Center of modENCODE (http://modencode.org), and much of the data are also available from the Drosophila Genomic Resources Center (https://dgrc.cgb.indiana.edu/) and FlyBase (http:// flybase.org/).)