Empty spiracles, a gap gene containing a homeobox involved in Drosophila head development

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• The empty spiracles (ems) gene in Drosophila melanogaster is essential for head and posterior spiracle formation.
• Previous genetic mapping localized the ems locus to region 88A.

Purpose of the Study:

• To identify and characterize the gene responsible for the empty spiracles (ems) phenotype.
• To elucidate the expression patterns and regulatory mechanisms of the ems gene during Drosophila development.

Main Methods:

• Cross-homology screening using a Drosophila muscle segment homeobox (msh) probe to isolate candidate genes.
• Sequence analysis of W13 in ems mutant alleles.
• RNA expression analysis using Northern blotting and in situ hybridization.
• Gene fusion assays to identify cis-acting regulatory elements.

Main Results:

• Isolation of a homeobox-containing gene, W13, which was identified as the ems gene through sequence analysis of mutant alleles.
• A 2.4 kb ems transcript is expressed throughout embryonic and larval stages.
• Early ems expression in an anterior band is regulated by the bicoid (bcd) morphogen, with identified cis-acting elements.
• Later ems expression occurs in lateral regions (tracheal pits, neuroblasts) and posterior spiracles, correlating with observed defects in ems embryos.
• The predicted ems protein contains a homeodomain, a proline-rich N-terminus, and an acidic C-terminus, suggesting a transcription factor role.

Conclusions:

• W13 is confirmed as the empty spiracles (ems) gene, vital for Drosophila head and spiracle development.
• The study reveals ems acts as an anterior gap gene, regulated by bicoid, and later functions in tracheal and neuroblast development.
• The protein's structural features support its function as a transcription factor.