Homeotic genes and regional specification in Drosophila: characterization of the abdominalA gene and mechanisms of transcriptional control by homeotic proteins

During animal development, different regions of an embryo acquire distinct identities. In Drosophila melanogaster, morphological distinctions along the anterior-posterior axis require the function of homeotic genes. Homeotic genes are expressed in complex, overlapping patterns along the anterior-posterior axis in a manner that suggests they provide positional information to the developing organism. The homeotic genes encode related proteins that can control the transcriptional activity of other genes. Thus, regional identity appears to arise from position-specific patterns of gene expression under the control of homeotic genes. One of the homeotic genes, abdominal-A, is shown here to encode multiple, electrophorelically distinct proteins and to be expressed in different types of cells and tissues. Some of the cell-specific expression of abdominal-A protein is shown to be controlled post-transcriptionally. Finally, by studying the control of a regulatory target regulated by abdominal-A and another homeotic gene, Ultrabithorax, I demonstrate that homeotic proteins establish cell-type-specific, regional patterns of gene expression through complex interactions with the control elements of their target genes.