The in situ localization of Adh transcripts in Drosophila species reveals evolved regulatory differences in spatially restricted expression.

Spatial and temporal aspects of Adh expression were examined during oogenesis and embryogenesis of Drosophila melanogaster, D. simulans, and D. virilis by in situ hybridization. In stage 14 and 15 embryos, differences in zygotic expression of Adh in the primordia of the gastric caecae of D. simulans and in the fat body of D. virilis were observed. These zygotic differences appear to be transient because Adh expression is seen in the gastric caecae of stage 16 embryos of D. simulans and in the fat body of stage 17 embryos of D. virilis. Analysis of D. melanogaster x D. simulans hybrids revealed that the parental difference for transcriptional activity of Adh in the primordia of the gastric caecae is under dominant control. These results provide the basis for exploring evolved regulatory differences in Adh expression during oogenesis and embryogenesis of Drosophila, which are until now unexplored. The potential of in situ hybridization in analyzing evolved regulatory differences in gene expression is briefly discussed.