Developmental expression pattern of a 800 kb DNA continuum cloned from the Drosophila X chromosome 14B-15B region.

The expression throughout development of a long DNA segment from the Drosophila genome was investigated. A near continuum of 800 kb DNA was cloned by extending a 90 kb previous chromosome walk, spanning the rudimentary locus (r), and by initiating 2 chromosome walks from an isolated DNA clone located next to the r locus. Hexanucleotide-primed single strand cDNAs were synthesized from poly(A)+ RNAs prepared from staged embryos, larvae, pupae, males, females, heads from adults and thoraces plus abdomens from adults. The representativity of the cDNAs with regard to the whole length and the molar abundance of a selected gene mRNA was checked. These cDNAs were then used to probe Southern transfers of the cloned DNA after digestion with combinations of restriction enzymes. The limits of the expressed parts of the cloned DNA and their developmental profiles were then deduced. Data show that, in contrast to what was known on the basis of genetic analysis, this region of the Drosophila genome is densely transcribed. Numerous parts of the cloned DNA are found to be stage-, or sex- or territory-specifically expressed. Data are consistent with a view of the organization of this representative part of the Drosophila genome according to which the expressed regions tend to be clustered, whereas no tendency for transcription units displaying comparable specific spatial, temporal or sex expression patterns to be arranged in groups is noted.