The pattern of bristles and other sensory organs on the adult cuticle of Drosophila is prefigured in the imaginal discs by the pattern of expression of the proneural achaete (ac) and scute (sc) genes, two members of the ac-sc complex (AS-C). These genes are simultaneously expressed by groups of cells (the proneural clusters) located at constant positions in discs. Their products {transcription factors of the basic-helix-loop-helix family) allow cells to become sensory organ mother cells (SMCs), a fate normally realized by only one or a few cells per cluster. Here we show that the highly complex pattern of proneural clusters is constructed piecemeal, by the action on ac and sc of site-specific, enhancer-like elements distributed along most of the AS-C (-90 kb). Fragments of AS-C DNA containing these enhancers drive reporter lacZ genes in only one or a few proneural clusters. This expression is independent of the ac and sc endogenous genes, indicating that the enhancers respond to local combinations of factors (prepattern). We show further that the cross-activation between ac and sc, discovered by means of transgenes containing either ac or sc promoter fragments linked to lacZ and thought to explain the almost identical patterns of ac and sc expression, does not occur detectably between the endogenous ac and sc genes in most proneural clusters. Our data indicate that coexpression is accomplished by activation of both ac and sc by the same set of position-specific enhancers.

A case of illegal cattle purchasing is presented. Basque country police submitted six blood samples: three from the allegedly stolen animals and three from the putative mothers. Four polymorphic DNA loci were analyzed to establish the parental relationship. From the case investigation the maternity of the alleged cattle was determined.

Several genes of the achaete-scute complex (AS-C) of Drosophila melanogaster encode a 60 amino acids long conserved domain which shares a significant homology with a region of the vertebrate myc proteins. Based on these results, the existence of a family of Drosophila genes that would share both this conserved domain and the neurogenic function of the AS-C has been postulated. To test this proposal, we have searched a D. melanogaster genomic library with a probe that encodes the conserved domain. Only under very low stringency hybridization conditions, clones not belonging to the AS-C cross-hybridized with the probe. Those that gave the strongest signals were characterized. Sequencing of the cross-hybridizing regions showed that they had no significant homology with the conserved domain, the sequence similarity extending at the most for 37 nucleotides. Although our results do not conclusively disprove the existence of a family of AS-C-like genes, they indicate that the conservation of the domain would be lower than that found for shared motifs in other families of Drosophila developmental genes.

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