THE DROSOPHILA SRF HOMOLOG IS EXPRESSED IN A SUBSET OF TRACHEAL CELLSAND MAPS WITHIN A GENOMIC REGION REQUIRED FOR TRACHEAL DEVELOPMENT

The Drosophila homolog of the vertebrate serum response factor (SRF) w as isolated by low stringency hybridization. Nucleotide sequence analy sis revealed that the Drosophila SRF homolog (DSRF) codes for a protei n that displays 93% sequence identity with human SRF in the MADS domai n, the region required for DNA binding, dimerization and interaction w ith accessory factors. The DSRF gene isexpressed during several phases of embryonic development. In the egg, both the RNA and the protein ar e maternal in origin and slowly decrease in amount during gastrulation . After germ band retraction, high levels of zygotic expression are ob served in a distinct subset of peripheral tracheal cells distributed t hroughout the embryo. Many of these cells are at the tip of tracheal b ranches and are in direct contact with the target tissues. The DSRF ge ne was mapped toposition 60C on the second chromosome, and overlapping deficiencies which remove the gene were identified. Analysis of trach eal development in embryos carrying these deletions revealed a degener ation of most of the major branches of the tracheal system. Although t he initial migration of tracheal cells was not affected in those defic ient embryos, many tracheal cells appeared not to maintain their corre ct position and continued to migrate. Thus, the DSRF gene mightplay a role in the proper formation and maintenance of the trachea.