First detailed comparative, developmental and pathological analysis of the relationship between limb soft and hard tissues: muscle configuration is mainly related to the topological position, and not the anlage and/or homeotic identity, of digits (919.5)

In the last decades evolutionary developmental biologists have studied the ontogeny of hard and soft tissues in model organisms such as chicken, axolotl, frogs and mice. However, very few researchers have undertaken detailed analyses about the specific relationships between the soft and hard tissues of the tetrapod limbs and particularly of their autopodia (hand/foot) and zeugopodia (forearm/leg). We have therefore addressed this subject by using a wide range of different techniques in a broad taxonomic sample, including developmental and regenerative studies of GFP salamanders, ontogenetic studies of wildtype frogs, comparative studies of all major groups of tetrapods, and dissections of humans with birth defects involving polydactyly and digit reduction. Interestingly, our results show that in almost all cases of both wildtype and non‐wildtype non‐pentadactyly the identity and configuration of muscles is actually highly predictable and is mainly related to the topological position of the digits (e.g., by being the most ulnar/fibular, or instead the most radial/tibial digits) to which the muscles insert, and not to the ontogenetic anlage from which the digits develop or even the homeotic identity of each digit. We will discuss various case studies illustrating this point, and discuss the broader implications of our results for evolutionary, comparative and developmental biology and for human medicine. Grant Funding Source : Faculty Start‐Up Package, Howard University College of Medicine