Origins of context-dependent gene repression by capicua

Area of Science:

• Molecular Biology
• Developmental Biology
• Evolutionary Biology

Background:

• Receptor Tyrosine Kinase (RTK) signaling regulates gene expression through downstream targets.
• Capicua (Cic) is a transcriptional repressor that is downregulated by RTK signaling.
• Two Cic isoforms, Cic-L and Cic-S, exist in both Drosophila and mammals, with unclear functional differences.

Purpose of the Study:

• Investigate the functional significance and mechanism of action of Drosophila Cic isoforms.
• Determine the role of the Groucho (Gro) corepressor in Cic-mediated repression.
• Elucidate the evolutionary origins of Cic isoform-specific functions.

Main Methods:

• Utilized Drosophila melanogaster as a model organism.
• Employed genetic analysis to study Cic and Gro interactions.
• Investigated the function of a novel peptide motif (N2) in Cic-S.

Main Results:

• Drosophila Cic requires the Groucho (Gro) corepressor for function in early embryos via a novel N2 motif unique to Cic-S.
• The N2 motif is an evolutionary innovation within dipteran insects, absent in the ancestral Cic-L form.
• Cic-L is inactive in early embryos without the N2 motif, highlighting its essential role.
• Mammalian Cic proteins likely do not use Gro, and their Cic-S evolved independently.

Conclusions:

• The N2 motif in Drosophila Cic-S confers essential Gro-dependent activity for early embryonic development.
• Cic-S and Gro co-regulation facilitated the evolution of complex Torso RTK signaling networks in flies.
• Distinct repressor mechanisms and evolutionary changes characterize Cic proteins across species.