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Following publication of the original article [1], the authors reported the following errors.

Structural rearrangements of the genome resulting in genic imbalance due to copy number change are often deleterious at the organismal level, but are common in immortalized cell lines and tumors, where they may be an advantage to cells. In order to explore the biological consequences of copy number changes in the Drosophilagenome, we resequenced the genomes of 19 tissue-culture cell lines and generated RNA-Seq profiles. Our work revealed dramatic duplications and deletions in all cell lines. We found three lines of evidence indicating that copy number changes were due to selection during tissue culture. First, we found that copy numbers correlated to maintain stoichiometric balance in protein complexes and biochemical pathways, consistent with the gene balance hypothesis. Second, while most copy number changes were cell line-specific, we identified some copy number changes shared by many of the independent cell lines. These included dramatic recurrence of increased copy number of the PDGF/VEGF receptor, which is also over-expressed in many cancer cells, and of bantam, an anti-apoptosis miRNA. Third, even when copy number changes seemed distinct between lines, there was strong evidence that they supported a common phenotypic outcome. For example, we found that proto-oncogenes were over-represented in one cell line (S2-DRSC), whereas tumor suppressor genes were under-represented in another (Kc167). Our study illustrates how genome structure changes may contribute to selection of cell lines in vitro. This has implications for other cell-level natural selection progressions, including tumorigenesis.

The three Drosophila EcR isoforms differ only at their N termini;thus, they share the conserved ligand-binding domain transcriptional activation function (AF2) and only differ in the unconserved A/B region, which contains a second, isoform-specific, activation function (AF1). We have developed a dominant-negative mutant EcR (EcR-DN), expressed it in flies with the GAL4/UAS system, and used it to block ecdysone signaling in eight tissues or groups of tissues. Localized EcR-DN arrests ecdysone-dependent development in the target cells and often — because of a molting checkpoint —arrests development globally. Simultaneously expressing individual wild-type EcR isoforms in the same target tissues suppresses the EcR-DN phenotype and identifies the rescuing isoform as sufficient to support the development of the target. Every isoform, and even an N-terminal truncated EcR that lacks any AF1, supports development in the fat body, eye discs, salivary glands,EH-secreting neurosecretory cells and in the dpp expression domain,implying that AF1 is dispensable in these tissues. By contrast, only EcR-A is able to support development in the margins of the wing discs, and only EcR-B2 can do so in the larval epidermis and the border cells of the developing egg chamber. In light of our results, the simplest explanations for the widespread spatial and temporal variations in EcR isoform titers appear untenable.

Cells of the line Kc, derived fromDrosophila melanogaster embryos, extend long processes when exposed to ecdysteroid hormones. We have devised a quantitative assay for this morphological response, using the subline Kc-H. The assay was used to characterize the conditions required for the response. A halfmaximal response is elicited by approximately 10-8M 20-hydroxyecdysone; the response is saturated by 10-7M 20-hydroxyecdysone, which causes detectable elongation within a few hours, and a maximal response after 2–3 days. The response occurs substantially normally in the absence of serum, during growth in suspension, and in over-crowded cultures. It is not elicited by cyclic nucleotides, vertebrate growth factors, or a variety of other non-ecdysteroid reagents. Of 60 ecdysteroid compounds tested, only those which were active in other insect test systems elicited the response, and the concentrations required were approximately proportional to the concentrations active in other in vitro systems. We conclude that the response of Kc cells to 20-hydroxyecdysone retains basic features of the ecdysteroid response of intact tissues and therefore that Kc cells are a useful model system for studying ecdysteroid action.

Abstract: We report that cells of aDrosophila embryonic cell line (Kc167 cells) can be readily and stably transformed by transposition of P elements from exogenous DNA. Cells are transfected with plasmids carrying methotrexate- or α-amanitin-resistance markers expressed from constitutive promoters and co-transfected with a gene encoding a somatically active transposase. Transient expression of the transposase leads to efficient production of transformed, resistant cells. We describe conditions under which most resistant clones are healthy and harbor a small number (1–50) of transposons and few (≤5%) retain plasmid sequences derived from illegitimate recombination. Using conditions like these it should prove possible to construct enhancer trap and/or gene libraries usingDrosophila cells.

The neurogenic loci Notchand Delta, which both encode EGF-homologous transmembrane proteins, appear to function together in mediating cell-cell communication and have been shown to interact at the cell surface in vitro. To examine the role of the EGF repeats in this interaction, we performed an extensive deletion mutagenesis of the extracellular domain of Notch. We find that of the 36 EGF repeats of Notch, only two, 11 and 12, are both necessary and sufficient to mediate interactions with Delta. Furthermore, this Deltabinding ability is conserved in the corresponding two repeats from the Xenopus Notchhomolog. We report a novel molecular interaction between Notchand Serrate, another EGF-homologous transmembrane protein containing a region of striking similarity to Delta, and show that the same two EGF repeats of Notchalso constitute a Serratebinding domain. These results suggest that Notchmay act as a multifunctional receptor whose 36 EGF repeats form a tandem array of discrete ligand-binding units, each of which may potentially interact with several different proteins during development.

SYNOPSIS. In the Drosophila Kc-H cell line ecdysteroids cause rapid increases in the synthesis of two groups of polypeptides which we call ecdysteroid-inducible polypeptides. We have shown that these changes occur at least in part at the level of mRNA titers and we have isolated cDNA clones corresponding to the mRNAs for these polypeptides. The increases in these mRNAs may well be among the primary hormone effects.