Re-evaluating the morphological evidence for the re-evolution of lost mandibular teeth in frogs.

Dollo's law of irreversibility states that once a complex structure is lost, it cannot be regained in the same form. Several putative exceptions to Dollo's law have been identified using phylogenetic comparative methods, but the anatomy and development of these traits are often poorly understood. Gastrotheca guentheri is renowned as the only frog with teeth on the lower jaw. Mandibular teeth were lost in the ancestor of frogs more than 200 million years ago and subsequently regained in G. guentheri. Little is known about the teeth in this species despite being a frequent example of trait "re-evolution," leaving open the possibility that it may have mandibular pseudoteeth. We assessed the dental anatomy of G. guentheri using micro-computed tomography and histology and confirmed the longstanding assumption that true mandibular teeth are present. Remarkably, the mandibular teeth of G. guentheri are nearly identical in gross morphology and development to upper jaw teeth in closely related species. The developmental genetics of tooth formation are unknown in this possibly extinct species. Our results suggest that an ancestral odontogenic pathway has been conserved but suppressed in the lower jaw since the origin of frogs, providing a possible mechanism underlying the re-evolution of lost mandibular teeth.

Development and regeneration of the crushing dentition in skates (Rajidae).

Sharks and rays (elasmobranchs) have the remarkable capacity to continuously regenerate their teeth. The polyphyodont system is considered the ancestral condition of the gnathostome dentition. Despite this shared regenerative ability, sharks and rays exhibit dramatic interspecific variation in their tooth morphology. Ray (batoidea) teeth typically constitute crushing pads of flattened teeth, whereas shark teeth are pointed, multi-cuspid units. Although recent research has addressed the molecular development of the shark dentition, little is known about that of the ray. Furthermore, how dental diversity within the elasmobranch lineage is achieved remains unknown. Here, we examine dental development and regeneration in two Batoid species: the thornback skate (Raja clavata) and the little skate (Leucoraja erinacea). Using in situ hybridization and immunohistochemistry, we examine the expression of a core gnathostome dental gene set during early development of the skate dentition and compare it to development in the shark. Elasmobranch tooth development is highly conserved, with sox2 likely playing an important role in the initiation and regeneration of teeth. Alterations to conserved genes expressed in an enamel knot-like signalling centre may explain the morphological diversity of elasmobranch teeth, thereby enabling sharks and rays to occupy diverse dietary and ecological niches.

Effect of Visual Art School-Based Stroke Intervention for Middle School Students.

BACKGROUND: Community stroke awareness initiatives have traditionally been used to expand knowledge of stroke signs and risk factors to high-risk adult populations. Here, we use a novel unfettered, visual art-based approach for an elementary school initiative to raise stroke awareness. METHODS: Seventh graders in a middle school art class received stroke awareness training during the course of the 2015 to 2016 school year through their teacher in the visual arts class. In turn, they used this training to develop their own artistic interpretations of key stroke awareness concepts via project-based learning and then present their projects to raise awareness about stroke. We evaluated our predata and postdata to determine whether the visual art school-based stroke intervention was effective in both educating students about stroke and enabling them to effectively disseminate this information to parents and other adults in their community. RESULTS: The pretest evaluation indicates a fair or good knowledge about stroke, and no student indicated an "outstanding" or "excellent" knowledge. The posttest evaluation indicated a higher degree of stroke awareness because students were rated as having an "outstanding," "excellent," or "very good" performance especially in the ability to translate knowledge of stroke awareness lessons learned in their art class into a well-articulated stroke-related project and presentation. Pearson χ test reveals significant difference (P < .001) between the pretest and posttest evaluations. CONCLUSIONS: Our results indicate that our school-based stroke intervention was effective in both educating students about stroke and enabling them to effectively disseminate this information to parents and other adults in their community. The use of a visual art teacher to lead the educational component in the intervention indicates that expertise in neurology or stroke is not necessary to facilitate understanding of stroke and highlights the importance of creativeness in stroke education for children.