Danielle Dhouailly

The specification of feather and scale protein synthesis in epidermal-dermal recombinations.

Abstract Keratin proteins synthesized by dorsal or tarsometatarsal embryonic chick epidermis in heterotopic and heterospecific epidermal-dermal recombinants were analyzed by polyacrylamide gel electrophoresis and were compared to those produced by normal nondissociated dorsal and tarsometatarsal embryonic skin, as well as to those produced by control homotopic recombinants. Recombinant skins were grafted on the chick chorioallantoic membrane and grown for 8 or 11 days. Recombinants comprising dorsal feather-forming dermis formed feathers, irrespective of the origin of the epidermis. The electrophoretic band patterns of the keratins extracted from these feathers were of typical feather type. Conversely recombinants comprising tarsometatarsal scale-forming dermis formed scales, irrespective of the origin of the epidermis. The band patterns of the keratins extracted from the epidermis of these scales were of typical scale type. Heterospecific recombinants comprising chick dorsal feather-forming epidermis and mouse plantar dermis gave rise to six footpads arranged in a typical mouse pattern. In these recombinants, the chick epidermis produced keratins, the band pattern of which was of typical chick scale type. These results demonstrate that the dermis not only induces the formation of cutaneous appendages in confirmity with its regional origin, but also triggers off in the epidermis the biosynthesis of either of two different keratin types, in accordance with the regional type (feather, scale, or pad) of cutaneous appendages induced. The possible relationship between region-specific morphogenesis and cytodifferentiation is discussed in comparison with results obtained in other kinds of epithelial-mesenchymal interactions.

Formation of Cutaneous Appendages in Dermo-Epidermal Recombinations between Reptiles, Birds and Mammals

Summary1.Previous experiments on dermo-epidermal recombinations between birds and mammals have shown that the class-specific quality of the cutaneous appendages depends on intrinsic properties of the epidermis but that several steps of their morphogenesis are controlled by the dermis. This morphogenetic interplay has been tested further in new experiments with reptilian skin.2.Reconstituted homo- and heterospecific skin explants, involving epidermis and dermis of lizard, chick and mouse, were cultured for 8 days on the chorioallantoic membrane of the chick embryo.3.Homospecific recombinations of dorsal, caudal or ventral lizard epidermis and dorsal lizard dermis gave rise to small dorsal-type scales. Recombinants of dorsal, caudal or ventral lizard epidermis and ventral lizard dermis gave rise to large ventral-type scales.4.Heterospecific recombinations of dorsal, caudal or ventral lizard epidermis and chick dermis from the glabrous comb region did not differentiate any scale structures.5.Heterospecific recombinations of dorsal or caudal lizard epidermis and tarsometatarsal chick dermis formed large chick-type scales.6.Heterospecific recombinations of dorsal, caudal or ventral lizard epidermis and chick feather-forming, or mouse hair-forming or whisker-forming dermis gave rise to tubercular scale primordia. The diameter and distribution of these primordia were in conformity with the feather, pelage hair and vibrissal patterns respectively.7.Heterospecific association of lizard dermis and chick or mouse epidermis led to the formation of few epidermal placode-like pegs; those differentiated by the mouse epidermis were interpreted as hair bud structures.8.The differentiation of reptilian scales is the result of dermo-epidermal interactions. Reptilian epidermis, when confronted with either reptilian, avian, or mammalian dermis, always responds to the dermal messages by forming scale buds. For final scale morphogenesis, however, reptilian dermis or avian scale-forming dermis is required. Reptilian dermis appears to be unable to induce extensive appendage formation in avian or mammalian epidermis.9.A remarkable similarity exists in the mechanisms of skin differentiation in the three classes of amniotes. Indeed scales, feathers and hairs require two kinds of dermal messages for their complete morphogenesis: early ones, which can be transmitted from one class to another, and which are responsible for the initiation, site, size and distribution pattern of appendage primordia, whose class-specific quality (scale, feather or hair buds) is determined by the epidermis; and later specific ones which can only be understood within the class and which are necessary for the completion of the specific architecture of the cutaneous appendage.Résumé1.Les résultats dexpériences précédentes de recombinaisons dermo-épidermiques entre Oiseaux et Mammifères ont montré que la qualité spécifique des phanères est déterminée par lépiderme, mais que diverses étapes de leur morphogenèse sont sous la dépendance du derme. Il était intéressant de reprendre ce type dexpériences avec de la peau de Reptile.2.Les fragments de peau reconstituée homo- et hétérospécifique, comprenant derme et épiderme des trois classes, ont été cultivés pendant 8 jours sur la membrane chorioallantoïdienne du poulet.3.Les associations homospécifiques lézard/lézard dépiderme dorsal, caudal ou ventral et de derme dorsal ont abouti à la formation de petites écailles de type dorsal; celles dépiderme dorsal, caudal ou ventral et de derme ventral à la formation de grandes écailles de type ventral.4.Les associations hétérospécifiques dépiderme dorsal, caudal et ventral de lézard et de derme de crête de poulet nont pas formé de phanères.5.Les associations hétérospécifiques dépiderme dorsal et caudal de lézard et de derme tarsométatarsien de poulet ont formé des écailles de type poulet.6.Les associations hétérospécifiques dépiderme dorsal, caudal et ventral de lézard et de derme ptilogène de poulet et trichogène de souris ont formé des bourgeons décaille dont le diamètre et la disposition sont conformes à la qualité spécifique et régionale du derme employé (derme dorsal de poulet, derme dorsal ou derme de lèvre supérieure de souris).7.Les associations hétérospécifiques de derme de lézard et dépiderme de poulet ou de souris ont formé quelques rares placodes épidermiques, qui ont été interprétées comme des bourgeons pileux dans le cas de lépiderme de souris.8.La différenciation des écailles de Reptile résulte dinteractions dermo-épidermiques. Lépiderme de Reptile répond toujours aux messages morphogènes issus dun derme de Reptile, dOiseau ou de Mammifère en formant des bourgeons décaille. Cependant, la transformation de ces bourgeons en écailles requiert le contact dun derme lépidogène, derme de Reptile ou bien encore derme de patte dOiseau. Le derme de Reptile apparaît incapable dinduire la formation de nombreux phanères dans un épiderme dOiseau ou de Mammifère.9.Dans les trois classes dAmniotes, les mécanismes de la différenciation de la peau présentent une remarquable similitude. En effet, la morphogenèse des écailles, des plumes et des poils requiert deux sortes de messages dermiques: les uns, précoces, pouvant être compris et interprétés par un épiderme dune autre classe zoologique, sont responsables du déclenchement de la morphogenèse et de lemplacement, taille et disposition des bourgeons de phanères dont la qualité spécifique (bourgeons scutellaires, plumaires ou pileux) est déterminée par lépiderme. Les autres, plus tardifs et spécifiques, sont interprétables seulement par lépiderme de la même classe et contiennent des informations nécessaires á lorganisation architecturale de lécaille, de la plume et du poil.

Dorsal dermis development depends on a signal from the dorsal neural tube, which can be substituted by Wnt-1.

To investigate the origin and nature of the signals responsible for specification of the dermatomal lineage, excised axial organs in 2-day-old chick embryos were replaced by grafts of the dorsal neural tube, or the ventral neural tube plus the notochord, or aggregates of cells engineered to produce Sonic hedgehog (Shh), Noggin, BMP-2, Wnt-1, or Wnt-3a. By E10, grafts of the ventral neural tube plus notochord or of cells producing Shh led to differentiation of cartilage and muscles, and an impaired dermis derived from already segmented somites. In contrast, grafts of the dorsal neural tube, or of cells producing Wnt-1, triggered the formation of a feather-inducing dermis. These results show that the dermatome inducer is produced by the dorsal neural tube. The signal can be Wnt-1 itself, or can be mediated, or at least mimicked by Wnt-1.

Localisation of members of the notch system and the differentiation of vibrissa hair follicles: receptors, ligands, and fringe modulators.

Hair vibrissa follicle morphogenesis involves several cell segregation phases, in the dermis as well as in the epidermis. The expression of Notch‐related genes, which are well established mediators of multiple cell segregation events in Drosophila development, was studied by in situ hybridisation during embryonic mouse vibrissa follicle morphogenesis and the first adult hair cycle. The results show that two receptors, Notch1 and ‐2, three ligands, Delta1, Serrate1, and ‐2, and the three Fringe regulators, Lunatic, Manic, and Radical, are expressed in different locations and morphogenetic stages. First, the appearance of hair vibrissa primordia involves the expression of complementary patterns of Notch2, Delta1, and Lunatic Fringe in the dermis and of Notch1, Serrate2, and Lunatic Fringe in the epidermis. Second, this expression pattern is no longer found after stage 3 in the dermis. Meanwhile, in the epidermis, the expression of Notch1, Serrate2, and Lunatic Fringe before the formation of the placode may be involved in determining two populations of epidermal cells in the developing follicle. Third, complementary expression patterns for Notch1, Manic, and Lunatic Fringe, as well as Serrate1 and ‐2 as previously shown (Powell et al., 1998 ), are progressively established from stage 4 of embryonic development both in the outer root sheath and in the hair matrix. These patterns are consistent with the one found in the adult anagen phase. During the hair vibrissa cycle, Notch1 and Manic Fringe display temporal and spatial changes of expression, suggesting that they may intervene as modulators of trichocyte activities. Dev Dyn 2000;218:426–437.

Avian scale development: XI. Initial appearance of the dermal defect in scaleless skin☆

The chicken mutant, scaleless, is characterized by the total absence of scutate scales. Previous experiments have shown that the scaleless defect is expressed by the epidermal cells while the dermal cells are able to participate in normal scale morphogenesis. However, in association with 14- to 16-day scaleless dermis, normal epidermis or the simple ectoderm of the chorion failed to develop scutate scale epidermis with its characteristic beta stratum. Thus the question arises: since the scaleless dermis starts out functioning normally, when does it become defective? Heterogenetic, heterotopic associations have been performed between 7.5-day to 11.5-day scaleless dermis and a neutral responding tissue, the midventral apteric epidermis, from 10.5-day normal embryos. The results show that up until 9.5 day of incubation the scaleless dermis is able to give instructions for normal scutate scale formation, if combined with normal epidermis. However, after 9.5 days, the scaleless dermis is not able to induce scale formation in normal apteric epidermis. Thus, the functional defect of the scaleless dermis occurs during the time (9 to 10 days of incubation) when epidermal placodes appear in normal embryos. From the present data, at least two explanations are possible. Either the scaleless epidermis is unable to respond to the placode inducing properties being provided by the scaleless dermis and because an epidermal placode does not form the scaleless dermis becomes defective, or the scaleless epidermis does not provide some earlier cue necessary for the scaleless dermis to acquire its placode inducing capabilities.

Regional specification of cutaneous appendages in mammals

SummaryThe problem of the regional specification of snout vibrissae and dorsal pelage hairs has been analysed in mouse embryos. Reconstituted homo-and heterotopic skin explants, consisting of epidermis and dermis from both regions, were cultured on the chorioallantoic membrane of the chick embryo.Recombinants of 12.5-day upper lip dermis and 12.5-day dorsal epidermis developed a small number of large vibrissal type follicles arranged in a recognizable rectangular vibrissal pattern. The reverse combinations of 12.5- or 14.5-day dorsal dermis and 11- to 12.5-day upper lip epidermis formed a single population of numerous and small follicles arranged in a typical pelage hair pattern (trio groups) or gave rise to a mixed population of follicles with both whiskers and pelage hairs.It is concluded that the dermis is responsible for the regional specification of the cutaneous appendages and their distribution pattern. However, at the time it was isolated, the upper lip epidermis already possesses the information for the morphogenesis of vibrissae, but remains malleable and responsive to the dermal influence.

CHOXC-8 and CHOXD-13 Expression in Embryonic Chick Skin and Cutaneous Appendage Specification

We studied the expression of two distantly clustered Hox genes which could, respectively, be involved in specification of dorsal feather‐ and foot scale‐forming skin in the chick embryo: cHoxc‐8, a median paralog, and cHoxd‐13, located at the 5′ extremity of the HoxD cluster. The cHoxc‐8 transcripts are present at embryonic day 3.5 (E3.5)in the somitic cells, which give rise to the dorsal dermis by E5, and at E6.5–8.5 in the dorsal dermal and epidermal cells during the first stages of feather morphogenesis. The cHoxd‐13 transcripts are present at E4.5–9.5 in the autopodial mesenchyme and at E10.5–12.5 in the plantar dermis during the initiation of reticulate scale morphogenesis. Both the cHoxc‐8 and cHoxd‐13 transcripts are no longer detectable after the anlagen stage of cutaneous appendage morphogenesis. Furthermore, heterotopic dermal–epidermal recombinations of dorsal, plantar, and apteric tissues revealed that the epidermal ability or inability to form feathers is already established by the time of skin formation. Retinoic acid (RA) treatment at E11 induces after 12 hr an inhibition of cHoxd‐13 expression in the plantar dermis, followed by the formation of feather filaments on the reticulate scales. When E7.5 dorsal explants are treated with RA for 6 days, they form scale‐like structures where the Hox transcripts are no more detectable. Protein analysis revealed that the plantar filaments, made up of feather β‐keratins, corresponded to a homeotic transformation, whereas the scale‐like structures, composed also of feather β‐keratins, were teratoid. These results strengthen the hypothesis that different homeobox genes play a significant role in specifying the regional identity of the different epidermal territories. Dev. Dyn. 1997;210: 274–287.© 1997 Wiley‐Liss, Inc.

Retinoic acid causes the development of feathers in the scale-forming integument of the chick embryo

SummaryInjection of retinoic acid (3×62.5 μg or 3×125 μg) into the amniotic sac of chick embryos between 10 and 12 days of incubation resulted in the formation of club-shaped feathers within the feather tracts, and the development of feathers in the scale-forming areas of the feet. The latter finding is interpreted as caused by a disturbance of the tissue interactions which occur in the skin of the feet at this time.

Use of retinoic acid for the analysis of dermal-epidermal interactions in the tarsometatarsal skin of the chick embryo☆

Feet of chicks are normally covered with scales. Injection of retinoic acid into the amniotic cavity of 10-day chick embryos causes the formation of feathers on the foot scales. To elucidate whether retinoic acid affects primarily the epidermis or the dermis, heterotypic dermal-epidermal recombinants of tarsometatarsal skin were tested as to their morphogenetic capacity, when grafted to the chick chorioallantoic membrane. Recombinants involving treated epidermis and untreated dermis formed feathered scales, while the reverse recombinants of untreated epidermis and treated dermis led to the formation of scales only. Likewise the association of treated tarsometatarsal dermis with untreated epidermis from a non-appendage-forming region (the midventral apterium) resulted in the formation of scales only. These results show that retinoic acid affects primarily the epidermis. Further insight into the mechanism of dermal-epidermal interaction was gained by heterotopic recombinations of early (8.5- and 10-day) untreated tarsometatarsal dermis with epidermis from the midventral apterium. These recombinants formed scales, proving that tarsometatarsal dermis is endowed with scale-forming properties as early as 8.5 days of incubation. Finally, it is concluded that retinoic acid acts on the chick foot epidermal cells by temporarily inhibiting their scale placode-forming properties, allowing their latent feather placode-forming properties to be expressed.

Early events in retinoic acid-induced ptilopody in the chick embryo

SummaryIntra-amniotic injection of 125 μg of retinoic acid to 10-day old chick embryos causes the formation of feathers on the scales of the anterior face of the tarsometatarsus.The early effects of retinoic acid (RA) on the chick foot integument have been studied between 12 h and 72 h following RA injections by two methods. Firstly, sequential fixation in glutaraldehyde and then osmium tetroxide to follow the early changes at the macroscopical and ultrastructural levels. Secondly, sequential grafts of contralateral samples on to chorioallantoic membrane (CAM) of nontreated chick embryos to test their morphogenetic performance and to determine the minimum time for RA to take effect.Results show that during the first 24 h RA causes morphological changes of both epidermal and dermal cells in almost half of the injected embryos. In particular, the dermal-epidermal junction is transformed from scale-type into feather-type. However, the development of grafted samples shows that feather morphogenesis is irreversibly undertaken only 24 to 48 h after the treatment. At this stage, roundish feather-like placodes are formed instead of the normal rectangular, scale placodes. The scales, the formation of which has been temporarily inhibited, resume their development between 48 h and 72 h after the the injection, proximally to the feather buds, so that feathers are finally carried by the distal tips of the scales.