Cataloging altered gene expression in young and senescent cells using enhanced differential display.

Recently, a novel PCR-based technique, differential display (DD), has facilitated the study of differentially expressed genes at the mRNA level. We report here an improved version of DD, which we call Enhanced Differential Display (EDD). We have modified the technique to enhance reproducibility and to facilitate sequencing and cloning. Using EDD, we have generated and verified a catalog of genes that are differentially expressed between young and senescent human diploid fibroblasts (HDF). From 168 genetags that were identified initially, 84 could be sequenced directly from PCR amplified bands. These sequences represent 27 known genes and 37 novel genes. By Northern blot analysis we have confirmed the differential expression of a total of 23 genes (12 known, 11 novel), while 19 (seven known, 12 novel) did not show differential expression. Several of the known genes were previously observed by others to be differentially expressed between young and senescent fibroblasts, thereby validating the technique.

Sequence and expression of IMP-L1, an ecdysone-inducible gene expressed during Drosophila imaginal disc morphogenesis.

Drosophila imaginal discs are induced by the steroid hormone 20-hydroxyecdysone to initiate morphogenesis leading to formation of the adult appendages and thoracic epidermis at the end of the third larval instar. Ecdysone-dependent transcriptional activation of a set of genes that encode imaginal disc transcripts found on membrane-bound polysomes precedes and may be responsible for some aspects of the cellular changes that mediate epithelial morphogenesis in this system. A 1.35 kb transcript from one of these genes, IMP-L1, is first observed in vivo at or just prior to pupariation, as ecdysone titers are peaking and beginning to decline. Expression is initiated in proximal areas of the antennal disc, later spreading to a more widespread but nonuniform distribution throughout other thoracic imaginal discs. IMP-L1 is not, however, expressed in other ecdysone target tissues such as salivary glands or fat body. The IMP-L1 gene encodes a novel protein product containing a signal peptide, a possible transmembrane domain, two highly charged domains and a proline rich C-terminal domain. We suggest that the delayed timing of expression of this secondary response gene is necessary for proper ordering of cellular events associated with disc morphogenesis.