Epigenetic Coalitions Couple Tissue Growth to Generate Periodic Colour Patterns in Birds

Area of Science:

• Developmental Biology
• Genetics
• Evolutionary Biology

Background:

• Periodic patterning is crucial for biological organization, with avian feather development offering a model for continuous patterning in expanding domains.
• The Agouti-signaling protein (ASIP) gene is a key player in determining coat and feather color patterns.

Purpose of the Study:

• To elucidate the regulatory mechanisms underlying ASIP gene expression during avian color patterning.
• To understand how epigenetic factors, chromatin structure, and tissue geometry interact to control discrete color outputs.
• To explore the evolutionary role of cis-regulatory elements and retrotransposon co-option in ASIP's function.

Main Methods:

• Utilized a neural-network-like computational architecture to model ASIP cis-regulatory function.
• Employed single-nucleus multiome and Micro-C techniques to map enhancer-silencer interactions.
• Conducted comparative analyses across tissues and species, alongside functional assays.

Main Results:

• The ASIP cis-regulatory landscape acts as a complex integration hub, processing signals related to morphogen feedback, chromatin topology, and tissue geometry.
• Identified stage- and context-specific enhancer-silencer coalitions and a negative-feedback loop involving Wnt signaling that couples patterning to domain expansion.
• Defined a conserved epigenetic grammar in cis-regulatory modules and demonstrated retrotransposon co-option expanding ASIP's regulatory repertoire.

Conclusions:

• ASIP's regulation provides a model for generating diverse, environmentally tunable color patterns through shifting epigenetic states.
• Findings support a Turing-principle-based communication model for pattern formation, driven by epigenetic coalitions.
• The study highlights the evolutionary plasticity of cis-regulatory elements in shaping adaptive coloration.