Molecular Basis of Variations in Facial Soft Tissues: Insights from Cichlids

The human face serves as a crucial component of attractiveness and identity, playing a pivotal role in social interactions. The genetic legacy of the human face reaches back to the evolution of the vertebrate jaw, via transformation of the third gill-arch of lamprey-like ancestors. Teleost fish models, particularly zebrafish, have offered valuable insights into the developmental and molecular mechanisms governing craniofacial skeletogenesis, owing to the molecular conservation in these processes. However, knowledge regarding the morphogenic processes shaping facial soft tissues remains surprisingly sparse. The diverse family of Cichlidae constitute ~10% of teleost fish species and represent an exceptional opportunity for evolutionary biology research due to their extensive ecological diversity and rapid speciation rates. Cichlid fishes also exhibit remarkable craniofacial morphological diversity, making them excellent models for studying both craniofacial skeletal and soft tissue morphogenesis. Utilizing the wealth of natural mutants within cichlid populations, this short review pitches cichlid fish models as valuable tools for investigating the genetic regulators and interactions underlying facial soft tissue formation. By synthesising developmental and regulatory mechanisms that influence morphological variations in facial soft tissues in cichlids and other model organisms, we create a blueprint for forthcoming molecular genetic investigations into facial diversity across various species and facial deformities in humans.