Evo-dévo de la voie Eda : de l’évolution du signaling à l’établissement de la morphologie

L'observation des nombreuses espèces au sein des métazoaires permet de rendre compte de leur formidable diversité de morphologies. Ces organismes complexes acquièrent leur plan d'organisation et leurs caractéristiques propres pendant le développement embryonnaire. Au cours de celui-ci, la morphogénèse des différentes structures anatomiques est contrôlée par des réseaux complexes de gènes intervenant dans des territoires et des moments précis. Comprendre quelles modifications des voies développementales au cours de l'évolution sont responsables de cette diversité constitue un champ important de la biologie moderne : l'évo-dévo. Pour comprendre ces modifications, il est important de pouvoir étudier ces changements sur des modèles facilement accessibles et qui possèdent une grande variabilité de formes. Les phanères des vertébrés répondent à ces critères : leur nombre, leur forme et leur taille ont été des caractères très variables au cours de la diversification des mammifères et les données déjà obtenues sur la souris permettent une expérimentation aisée. De nombreuses voies de signalisation sont impliquées dans le développement des phanères, mais une en particulier, impliquée spécifiquement dans le développement des appendices ectodermiques : la voie EDA, composée d'un ligand EDA, de son récepteur EDAR et d'un adaptateur spécifique EDARADD. Dans le but de mieux comprendre le rôle de la voie EDA au cours de l’évolution des mammifères, nous avons orienté ma thèse en 2 axes : le premier vise à étudier le rôle d’Edar dans le patterning de la dent chez la souris, et le second l’impact de la perte d’une des deux isoformes d’EDARADD au cours de l’évolution des mammifères.The observation of the numerous metazoan species highlights their wonderful morphological diversity. These complex organisms got their body plan and their specific traits during embryonic development. During development, complex gene networks that are tightly regulated through space and time, control morphogenesis. Understanding which modifications of developmental pathways are responsible for the establishment of this diversity is one of the key questions of the biological field: Evo-Devo. To understand these modifications, it is crucial to study accessible models that are representative of this diversity. To do that, ectodermal appendages are a very good model: their number, size, and shape are highly variable during mammals diversification and data had already shown that they exhibit natural variation. Numerous signaling pathways are implicated in their development but one is very specific to them: the Eda pathway and present an big interest for the study of their evolution. To better understand the role of the Eda pathway during mammals evolution, I orientated my thesis in two part: the first one study the impact of Edar in the establishment of the mouse dental tooth row and the second the impact of gain/loss of protein isoforms of the adaptor Edaradd on the evolution of this pathway

Non-model systems in mammalian forelimb evo-devo

Mammal forelimbs are highly diverse, ranging from the elongated wing of a bat to the stout limb of the mole. The mammal forelimb has been a long-standing system for the study of early developmental patterning, proportional variation, shape change, and the reduction of elements. However, most of this work has been performed in mice, which neglects the wide variation present across mammal forelimbs. This review emphasizes the critical role of non-model systems in limb evo-devo and highlights new emerging models and their potential. We discuss the role of gene networks in limb evolution, and touch on functional analyses that lay the groundwork for further developmental studies. Mammal limb evo-devo is a rich field, and here we aim to synthesize the findings of key recent works and the questions to which they lead

Conserved features and evolutionary shifts of the EDA signaling pathway involved in vertebrate skin appendage development.

International audienceIt is widely accepted that evolutionary changes in conserved developmental signaling pathways play an important role in morphological evolution. However, few in silico studies were interested in tracking such changes in a signaling pathway. The Ectodysplasin (EDA) pathway provides an opportunity to fill this gap because it is involved in vertebrate skin appendage development such as scales, teeth, hair, and feathers that take an obvious part in the adaptation of species to their environment. We benefited from the large amount of genomic data now available to explore the evolution of the upstream genes of the EDA pathway. In mammals, these genes are eda (encoding 2 ligands, EDA-A1 and EDA-A2), edar (EDA-A1 receptor), edaradd (EDA receptor [EDAR] adapter), xedar (EDA-A2 receptor), and troy (a XEDAR-related receptor). We show that the evolution of EDA pathway genes combines both strongly conserved features and evolutionary shifts. These shifts are found at different signaling levels (from the ligand to intracellular signaling) and at different taxonomic levels (class, suborder, and genera). Although conserved features likely participate to the similarities found in the early development of vertebrate skin appendages, these shifts might account for innovations and specializations. Moreover, our study demonstrates that we can now benefit from the large number of sequenced vertebrate genomes to explore the evolution of specific signaling pathways and thereby to open new perspectives for developmental biology and evolutionary developmental biology

Making a bat: The developmental basis of bat evolution.

Bats are incredibly diverse, both morphologically and taxonomically. Bats are the only mammalian group to have achieved powered flight, an adaptation that is hypothesized to have allowed them to colonize various and diverse ecological niches. However, the lack of fossils capturing the transition from terrestrial mammal to volant chiropteran has obscured much of our understanding of bat evolution. Over the last 20 years, the emergence of evo-devo in non-model species has started to fill this gap by uncovering some developmental mechanisms at the origin of bat diversification. In this review, we highlight key aspects of studies that have used bats as a model for morphological adaptations, diversification during adaptive radiations, and morphological novelty. To do so, we review current and ongoing studies on bat evolution. We first investigate morphological specialization by reviewing current knowledge about wing and face evolution. Then, we explore the mechanisms behind adaptive diversification in various ecological contexts using vision and dentition. Finally, we highlight the emerging work into morphological novelties using bat wing membranes

Making a bat: The developmental basis of bat evolution.

Bats are incredibly diverse, both morphologically and taxonomically. Bats are the only mammalian group to have achieved powered flight, an adaptation that is hypothesized to have allowed them to colonize various and diverse ecological niches. However, the lack of fossils capturing the transition from terrestrial mammal to volant chiropteran has obscured much of our understanding of bat evolution. Over the last 20 years, the emergence of evo-devo in non-model species has started to fill this gap by uncovering some developmental mechanisms at the origin of bat diversification. In this review, we highlight key aspects of studies that have used bats as a model for morphological adaptations, diversification during adaptive radiations, and morphological novelty. To do so, we review current and ongoing studies on bat evolution. We first investigate morphological specialization by reviewing current knowledge about wing and face evolution. Then, we explore the mechanisms behind adaptive diversification in various ecological contexts using vision and dentition. Finally, we highlight the emerging work into morphological novelties using bat wing membranes

A new developmental mechanism for the separation of the mammalian middle ear ossicles from the jaw.

Multiple mammalian lineages independently evolved a definitive mammalian middle ear (DMME) through breakdown of Meckel's cartilage (MC). However, the cellular and molecular drivers of this evolutionary transition remain unknown for most mammal groups. Here, we identify such drivers in the living marsupial opossum Monodelphis domestica, whose MC transformation during development anatomically mirrors the evolutionary transformation observed in fossils. Specifically, we link increases in cellular apoptosis and TGF-BR2 signalling to MC breakdown in opossums. We demonstrate that a simple change in TGF-β signalling is sufficient to inhibit MC breakdown during opossum development, indicating that changes in TGF-β signalling might be key during mammalian evolution. Furthermore, the apoptosis that we observe during opossum MC breakdown does not seemingly occur in mouse, consistent with homoplastic DMME evolution in the marsupial and placental lineages