The caudal homeodomain protein activates Drosophila E2F gene expression

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• The Drosophila caudal homeobox gene is essential for anteroposterior axis and gut development.
• Human homologs CDX1 and CDX2 regulate intestinal cell proliferation and differentiation, with Cdx2 primarily acting as a tumor suppressor.
• The role of Drosophila Caudal in cell proliferation remains uncharacterized.

Purpose of the Study:

• To investigate the influence of Drosophila Caudal on cell proliferation.
• To determine if Caudal regulates the Drosophila E2F (dE2F) gene.

Main Methods:

• Identified Caudal binding sequences in the 5'-flanking region of the dE2F gene.
• Utilized transient transfection assays to assess Caudal transactivation of the dE2F promoter.
• Employed transgenic flies with E2F-lacZ fusion genes (wild-type and mutated binding sites) and the GAL4-UAS system to study gene expression in vivo.
• Induced ectopic Caudal expression using heat shock to observe effects on larval development.

Main Results:

• Three Caudal binding sequences were identified in the dE2F 5'-flanking region.
• Transient transfection assays confirmed Caudal's role in transactivating the dE2F gene promoter.
• Transgenic fly analyses demonstrated that Caudal binding sites are necessary for dE2F expression in vivo.
• Ectopic Caudal expression led to the induction of melanotic tumors in Drosophila larvae.

Conclusions:

• Drosophila Caudal directly regulates dE2F gene expression.
• Caudal influences cell proliferation through the transactivation of the E2F gene.
• These findings suggest a role for Caudal in controlling cell growth and potentially tumor formation in Drosophila.