A Jurassic ornithischian dinosaur from Siberia with both feathers and scales

Feathers, not just for the birds? Theropod dinosaurs, thought to be the direct ancestors of birds, sported birdlike feathers. But were they the only feathery dino group? Godefroit et al. describe an early neornithischian dinosaur with both early feathers and scales. This seemingly feathery nontheropod dinosaur shows that feathers were not unique to the ancestors of birds and may even have been quite widespread. Science , this issue p. 451 </jats:p

Both Retinoic Acid Receptors α (RARα) and γ (RARγ) Are Able to Initiate Mouse Upper-Lip Skin Glandular Metaplasia

Embryonic mouse upper-lip skin explants treated with 16.7 μM all-trans retinoic acid (tRA) give rise to a glandular metaplasia of hair vibrissa follicles; however, at this concentration, tRA can activate not only the three retinoic acid receptors (RARα, β, and γ), but also the retinoid X receptors (RXRα, β, and γ) as a consequence of its isomerization to 9-cis retinoic acid. We therefore studied the respective roles of the RXR and RAR by treating RARα–/–, β–/–, and γ–/– skin explants with tRA and wild-type explants with synthetic retinoids specific for RXR or for each of the RAR. The null mutation of the RARα, RARβ, and RARγ genes did not prevent tRA-induced hair glandular metaplasia, but RARγ inactivation dramatically reduced its ratio. As demonstrated by treating explants with a RAR- or a RXR-specific panagonist (CD367 and Ro25–7386, respectively), RAR are primarily responsible for this metaplasia. The use of two retinoids (Ro40–6055, 8 × 10–3μM, or CD437, 7.7 × 10–2μM) that are believed to act, respectively, as a RARα- or a RARγ-specific agonist showed that both these receptors can initiate a metaplasia. In contrast, BMS453, a RARβ-specific agonist, was unable to give rise to any metaplasia. Nevertheless, the highest degrees and ratios of metaplasia were only obtained after treatment with the CD367 RAR panagonist, or with either Ro40–6055 or CD437 at a concentration sufficient to allow the activation of the three RAR, suggesting that RARβ activation is required for a metaplasia of all vibrissæ

The early origin of feathers

Feathers have long been regarded as the innovation that drove the success of birds. However, feathers have been reported from close dinosaurian relatives of birds, and now from ornithischian dinosaurs and pterosaurs, the cousins of dinosaurs. Incomplete preservation makes these reports controversial. If true, these findings shift the origin of feathers back 80 million years before the origin of birds. Gene regulatory networks show the deep homology of scales, feathers, and hairs. Hair and feathers likely evolved in the Early Triassic ancestors of mammals and birds, at a time when synapsids and archosaurs show independent evidence of higher metabolic rates (erect gait and endothermy), as part of a major resetting of terrestrial ecosystems following the devastating end-Permian mass extinction

Evo Devo of the Vertebrates Integument

All living jawed vertebrates possess teeth or did so ancestrally. Integumental surface also includes the cornea. Conversely, no other anatomical feature differentiates the clades so readily as skin appendages do, multicellular glands in amphibians, hair follicle/gland complexes in mammals, feathers in birds, and the different types of scales. Tooth-like scales are characteristic of chondrichthyans, while mineralized dermal scales are characteristic of bony fishes. Corneous epidermal scales might have appeared twice, in squamates, and on feet in avian lineages, but posteriorly to feathers. In contrast to the other skin appendages, the origin of multicellular glands of amphibians has never been addressed. In the seventies, pioneering dermal–epidermal recombination between chick, mouse and lizard embryos showed that: (1) the clade type of the appendage is determined by the epidermis; (2) their morphogenesis requires two groups of dermal messages, first for primordia formation, second for appendage final architecture; (3) the early messages were conserved during amniotes evolution. Molecular biology studies that have identified the involved pathways, extending those data to teeth and dermal scales, suggest that the different vertebrate skin appendages evolved in parallel from a shared placode/dermal cells unit, present in a common toothed ancestor, c.a. 420 mya

A new scenario for the evolutionary origin of hair, feather, and avian scales

In zoology it is well known that birds are characterized by the presence of feathers, and mammals by hairs. Another common point of view is that avian scales are directly related to reptilian scales. As a skin embryologist, I have been fascinated by the problem of regionalization of skin appendages in amniotes throughout my scientific life. Here I have collected the arguments that result from classical experimental embryology, from the modern molecular biology era, and from the recent discovery of new fossils. These arguments shape my view that avian ectoderm is primarily programmed toward forming feathers, and mammalian ectoderm toward forming hairs. The other ectoderm derivatives – scales in birds, glands in mammals, or cornea in both classes – can become feathers or hairs through metaplastic process, and appear to have a negative regulatory mechanism over this basic program. How this program is altered remains, in most part, to be determined. However, it is clear that the regulation of the Wnt/beta-catenin pathway is a critical hub. The level of beta-catenin is crucial for feather and hair formation, as its down-regulation appears to be linked with the formation of avian scales in chick, and cutaneous glands in mice. Furthermore, its inhibition leads to the formation of nude skin and is required for that of corneal epithelium. Here I propose a new theory, to be further considered and tested when we have new information from genomic studies. With this theory, I suggest that the alpha-keratinized hairs from living synapsids may have evolved from the hypothetical glandular integument of the first amniotes, which may have presented similarities with common day terrestrial amphibians. Concerning feathers, they may have evolved independently of squamate scales, each originating from the hypothetical roughened beta-keratinized integument of the first sauropsids. The avian overlapping scales, which cover the feet in some bird species, may have developed later in evolution, being secondarily derived from feathers

Factors involved in corneal epithelium differentiation and transdifferentiation

Chez l'embryon de poulet de 2/3 jours, Pax6 est exprimé dans les noyaux futurs tissus oculaires, le cerveau, ainsi que dans l'épithélium nasal et oral. Aprés l'individualisation de la cornée, Pax6 continue d'être exprimé tout au long de la vie non seulement embryonnaire, mais aussi de la vie adulte. Par contre, l'expression de Pax6 est éteinte aprés 7 jours d'incubation dans l'épithélium nasal et oral. L'expression de K12 : 14 jours d'incubation pour le poulet, 21 jours de gestation pour le lapin, et tout au long de la vie adulte. Cette expression est spécifique de l'épithélium cornéen. J'ai transfecté le cDNA codant pour une forme active de Pax6 chez l'embryon de poulet de 2.5 à 3 jours d'incubation. Le résultat est une orientation dorso/ventrale anormale de l'œil. Cependant aucune formation ectopique de tissus oculaires n'en a résulté. J'ai étudié le rôle du cristallin, présenté comme l'inducteur de la cornée. Contrairement à ce qui a été publié antérieurement, celui-ci est seulement requis pour la croissance de l'œil mais ni pour la migration des fibroblastes formar le stroma de la cornée, ni pour l'expression de K12 dans son épithélium. Afin d'étudier la question du rôle éventuel du stroma lors de l'activation des génes Pax6, puis K12, par recombinaisons épithélio/mésenchymateuses. Les expériences réalisées avec les tissus d'embryon de poulet montrent que Pax6 peut être éteint et le futur épithelium cornéen transformé en épiderme et en plumes seulement avant 5 jours d'incubation. L'insuffisance du nombre de donneurs pour les greffes de cornée est un challenge. Ni l'association avec un stroma cornéen, ni la transfection de Pax6 n'a permis d'obtenir ce résultat.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Voies de signalisation impliquées dans la différenciation du macropattern cutané ventral et micropattern chez les vertébrés

La peau des vertébrés contient des phanères (écailles, plumes, poils) regroupés dans des champs cutanés phanérogènes. Chez le poulet, ceux-ci sont séparés par des zones clairsemées (semi-aptéries) ou glabres (aptéries). Le macropattern définit l'organisation des différents champs cutanés les uns par rapport aux autres, alors que le micropattern qualifie le motif de distribution des phanères au sein d'un champ cutané phanérogène. La formation du micropattern au sein de la peau embryonnaire homogène formée de lépiderme et du derme nécessite la présence de facteurs moléculaires transmembrabaires et diffusibles. Notch 1, Notch2, Deltal et Serrate2, appartenant à la famille des molécules transmembranaires du système Notch, semblent être impliqués dans la ségrégation des primordia de phanères. L'espacement des primordia est contrôllé par des facteurs diffusibles incluant les BMPs et leus antagonistes dont Drm/Gremlin. L'expression de celui-ci dans le derme est régulée par macropattern, nous avons pris comme modèle expérimental la peau ventral du poulet qui dérive de la somatopleire embryonnaire. Elle contient à la fois un champ phanérogène, la ptéryle ventrale, et un champ glabre, l'aptérie médioventrale. Nos résultats suggèrent que Noggin et Shh, produits à 2 jours respectivement par le mésoderme intermédiaire et l'endoderme proximal, antagonisent la voie BMP4 et répriment l'expression de msxl au niveau du mésoderme somatopleural proximal qui donnera ultérieurement le derme de la ptéryle ventrale. Les transcrits msxl restent présents dans le mésoderme somatopleural distal au cours du développement. Leur localisation à 8.5 jours correspond à l'emplacement de l'aptérie médioventrale. La greffe des cellules produisant Noggin et Shh ont montré qu'ils sont capables d'agir en synergie pour provoquer la formation d'une ptéryle supplémentaire au niveau de la somatopleure extra-embryonnaire.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Spécification des progéniteurs du derme dorsal chez l'embryon de poulet et de souris

La peau des vertébrés amniotes requiert la présence d'un derme compétent à initier la formation de phanères (écailles, plumes ou poils). Cette thèse a permis de mettre en évidence deux populations de progéniteurs du derme dorsal dans le somite chez le poulet. La première est spécifiée dans la lèvre médiodorsale (LMD) du dermomyotome et exprime Wnt-11 sous le contrôle de Wnt-1 issu du tube neural. La deuxième est spécifiée dans le dermomyotome central et exprime En-1 sous le contrôle de l'ectoderme. Ces deux populations forment respectivement le mésenchyme médian et latéral du dos, expriment Dermo-1 et se densifient pour former le derme dense. Chez la souris, le mésenchyme médian est aussi formé par des progéniteurs issus de la LMD exprimant Wnt-11, mais se densifie en dernier. Les différences observées lors de l'établissement du derme dorsal se retrouvent lors de l'induction des phanères du dos, apparaissant d'abord dans la région médiane chez le poulet et latérale chez la souris.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Dermal condensation formation in the chick embryo: requirement for integrin engagement and subsequent stabilization by a possible notch/integrin interaction.

International audienceDuring embryonic development, feathers appear first as primordia consisting of an epidermal placode associated with a dermal condensation. When 7-day chick embryo dorsal skin fragments showing three rows of feather primordia are cultured, they undergo a complete reorganization, which involves the down-regulation of morphogenetic genes and dispersal of dermal fibroblasts, leading to the disappearance of primordia. This loss of organisation is followed by de novo differentiation events. We have used this model to study potential factors involved in the formation of dermal condensations. Activation of Integrins by extracellular Manganese or intracellular Calcium prevents the initial disappearance of the dermal condensations. New primordia formation occurs even after inhibition of the Notch pathway albeit with some fusion between primordia. In conclusion, dermal fibroblast migration requires beta1-Integrin whereas the stability of dermal condensations could depend on Notch/Integrin interaction