The role of Hox genes in the origins and diversification of beetle horns

ZATTARA, EDUARDO E.; MOCZEK, ARMIN P.

Hox Modules in Evolution and Development

CRC Press

Lugar: Boca Raton, FL; Año: 2023; p. 53 - 75

The discovery of Hox genes forever changed how we understandthe role of genomic architecture in the evolution of animal diversity, andforced us to reassess our view of evolutionary novelty and homology away frombinary concepts and toward more nuanced, layered gradients. Subsequent studieson the diversity of Hox gene functions resulted in a significant shift from thenotion of master regulator genes toward the concept of conditional regionalspecifiers conveying spatial information and enabling region specificregulation of downstream effectors of development. In the process, diverse new insightswere gained from studying Hox functions beyond traditional model species andembryonic development. Here we highlight one such species, horned beetles inthe genus Onthophagus, and what we have learned (through the study ofHox genes and other transcription factors) regarding the nature of what we callthe innovation gradient – that beginning with simple developmentalevolution and subsequent elaboration eventually yields structures that appear entirelynovel. In particular, we discuss the roles of developmental inertia and expressionlatency – the tendencyfor genes to remain active well past the stages in which they were originallyneeded – in enabling functional repurposing of genes and the scaffolding of theinnovation gradient.