Use of a new strategy to isolate and characterize 436 Drosophila cDNA clones corresponding to RNAs detected in adult heads but not in early embryos.

We describe a new strategy for producing tissue-specific cDNA libraries and subsequently identifying tissue-specific clones. This method was used to screen for cDNA clones corresponding to RNAs expressed in the Drosophila head that cannot be detected in the early embryo. RNA blots were used to assess the spatial and temporal patterns of expression of these RNAs. The ensemble of 436 head-not-embryo clones identified roughly 700 distinct RNAs that are differentially expressed in the Drosophila head. The RNA expression patterns can be classified into five major categories. it is argued that this ensemble of clones represents a large fraction of all genes differentially expressed in the adult head, but not detected in the early embryo. Many of these genes are likely to encode eye- and nervous system-specific products.