Reptile scale paradigm: Evo-Devo, pattern formation and regeneration

Abstract

The purpose of this perspective is to highlight the merit of the reptile integument as an experimental model. Reptiles represent the first amniotes. From stem reptiles, extant reptiles, birds and mammals have evolved. Mammal hairs and feathers evolved from Therapsid and Sauropsid reptiles, respectively. The early reptilian integument had to adapt to the challenges of terrestrial life, developing a multi-layered stratum corneum capable of barrier function and ultraviolet protection. For better mechanical protection, diverse reptilian scale types have evolved. The evolution of endothermy has driven the convergent evolution of hair and feather follicles: both form multiple localized growth units with stem cells and transient amplifying cells protected in the proximal follicle. This topological arrangement allows them to elongate, molt and regenerate without structural constraints. Another unique feature of reptile skin is the exquisite arrangement of scales and pigment patterns, making them testable models for mechanisms of pattern formation. Since they face the constant threat of damage on land, different strategies were developed to accommodate skin homeostasis and regeneration. Temporally, they can be under continuous renewal or sloughing cycles. Spatially, they can be diffuse or form discrete localized growth units (follicles). To understand how gene regulatory networks evolved to produce increasingly complex ectodermal organs, we have to study how prototypic scale-forming pathways in reptiles are modulated to produce appendage novelties. Despite the fact that there are numerous studies of reptile scales, molecular analyses have lagged behind. Here, we underscore how further development of this novel experimental model will be valuable in filling the gaps of our understanding of the Evo-Devo of amniote integuments.

Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany

“…The coexistence of scaly skin and bristle-like integumentary structures has been reported for other non-avian dinosaursalbeit not theropods (e. g., Psittacosaurus; MAYR et al 2002) -but it remains highly unusual. Nonetheless, such coexistence is not at odds with a wealth of laboratory experiments that have demonstrated that small groups of stem cells in scales can be stimulated by molecular perturbation to form active feather follicles that develop feathers (DHOUAILLY et al1980;WIDELITZ et al 2000WIDELITZ et al , 2003CHANG et al 2009). In fact, such "feathery scales" are regularly envisioned as an intermediate stage of models of feather evolution (CHANG et al 2009).…”

An injury-response mechanism conserved across kingdoms determines entry of the fungus Trichoderma atroviride into development

“…conidiation | stress | transcriptome T he study of responses to mechanical damage has implications for medical applications related to tissue regeneration and repair (1). A conserved defense mechanism is present in plants and animals, in which the production of reactive oxygen species (ROS) and lipid metabolism are essential to the response (2).…”

Sticking to the story: outstanding challenges in gecko-inspired adhesives

“…However, geckos are part of a lineage of tetrapods (sauropsids) whose success in dealing with desiccating terrestrial environments has involved many modifications to the skin (Chang et al, 2009). Gecko skin is actually a complex, dynamic, heterogeneous, multi-layered material, and there is evidence that lipids (fat) and proteins are both present at the contact interface (Alibardi et al, 2011;Hsu et al, 2012).…”