Skin Ectoderm Research Articles

Differential modularity of the mammalian Engrailed 1 enhancer network directs sweat gland development.

Enhancers are context-specific regulators of expression that drive biological complexity and variation through the redeployment of conserved genes. An example of this is the enhancer-mediated control of Engrailed 1 (EN1), a pleiotropic gene whose expression is required for the formation of mammalian eccrine sweat glands. We previously identified the En1 candidate enhancer (ECE) 18 cis-regulatory element that has been highly and repeatedly derived on the human lineage to potentiate ectodermal EN1 and induce our species' uniquely high eccrine gland density. Intriguingly, ECE18 quantitative activity is negligible outside of primates and ECE18 is not required for En1 regulation and eccrine gland formation in mice, raising the possibility that distinct enhancers have evolved to modulate the same trait. Here we report the identification of the ECE20 enhancer and show it has conserved functionality in mouse and human developing skin ectoderm. Unlike ECE18, knock-out of ECE20 in mice reduces ectodermal En1 and eccrine gland number. Notably, we find ECE20, but not ECE18, is also required for En1 expression in the embryonic mouse brain, demonstrating that ECE20 is a pleiotropic En1 enhancer. Finally, that ECE18 deletion does not potentiate the eccrine phenotype of ECE20 knock-out mice supports the secondary incorporation of ECE18 into the regulation of this trait in primates. Our findings reveal that the mammalian En1 regulatory machinery diversified to incorporate both shared and lineage-restricted enhancers to regulate the same phenotype, and also have implications for understanding the forces that shape the robustness and evolvability of developmental traits.

The genetics of ocular disorders: Insights from the zebrafish

Proper formation of the vertebrate eye requires a precisely coordinated sequence of morphogenetic events that integrate the developmental contributions of the skin ectoderm, neuroectoderm, and head mesenchyme. Disruptions in this process result in ocular malformations or retinal degeneration and can cause significant visual impairment. The zebrafish is an excellent vertebrate model for the study of eye development and disease due to the transparency of the embryo, its ex utero development, and its amenability to forward genetic screens. This review will present an overview of the genetic methodologies utilized in the zebrafish, a description of several zebrafish models of congenital ocular diseases, and a discussion of the utility of the zebrafish for assessing the pathogenicity of candidate disease alleles.

Activated Kras Alters Epidermal Homeostasis of Mouse Skin, Resulting in Redundant Skin and Defective Hair Cycling

Germline mutations in the RAS-mitogen-activated protein kinase (RAS/MAPK) pathway are associated with genodermatoses, characterized by cutaneous, cardiac, and craniofacial defects, and cancer predisposition. Whereas activating mutations in HRAS are associated with the vast majority of patients with Costello syndrome, mutations in its paralog, KRAS, are rare. To better understand the disparity among RAS paralogs in human syndromes, we generated mice that activate a gain-of-function Kras allele (Lox-Stop-Lox (LSL)-Kras(G12D)) in ectodermal tissue using two different Cre transgenic lines. Using Msx2-Cre or ligand-inducible keratin 15 (K15)-CrePR, the embryonic effects of activated Kras were bypassed and the effects of Kras(G12D) expression from its endogenous promoter were determined. We found that Kras(G12D) induced redundant skin, papillomas, shortened nails, and hair loss. Redundant skin was associated with basal keratinocyte hyperplasia and an increase in body surface area. Paradoxically, Kras(G12D) also prevented hair cycle activation. We find that Kras(G12D) blocks proliferation in the bulge region of the hair follicle, when activated through Msx2-Cre but not through K15-CrePR. These studies reveal that KRAS, although infrequently involved in RAS/MAPK syndromes, is capable of inducing multiple cutaneous features that grossly resemble human RAS/MAPK syndromes.

P63 regulates multiple signalling pathways required for ectodermal organogenesis and differentiation

Heterozygous germline mutations in p63, a transcription factor of the p53 family, result in abnormal morphogenesis of the skin and its associated structures, including hair follicles and teeth. In mice lacking p63, all ectodermal organs fail to develop, and stratification of the epidermis is absent. We show that the ectodermal placodes that mark early tooth and hair follicle morphogenesis do not form in p63-deficient embryos, although the multilayered dental lamina that precedes tooth placode formation develops normally. The N-terminally truncated isoform of p63 (DeltaNp63) was expressed at high levels in embryonic ectoderm at all stages of tooth and hair development, and it was already dominant over the transactivating TAp63 isoform prior to epidermal stratification. Bmp7, Fgfr2b, Jag1 and Notch1 transcripts were co-expressed with DeltaNp63 in wild-type embryos, but were not detectable in the ectoderm of p63 mutants. In addition, beta-catenin and Edar transcripts were significantly reduced in skin ectoderm. We also demonstrate that BMP2, BMP7 and FGF10 are potent inducers of p63 in cultured tissue explants. Hence, we suggest that p63 regulates the morphogenesis of surface ectoderm and its derivatives via multiple signalling pathways.

Perturbation of BMP signaling in somitogenesis resulted in vertebral and rib malformations in the axial skeletal formation.

Axial skeletons such as vertebrae, ribs, and scapulae develop from the embryonic somitic mesoderm through interactions with neural tube/notochord and skin ectoderm. Bone morphogenetic proteins (BMPs) seem to play important roles in these tissue interactions; however, the relationship between BMP signaling and the early development of axial skeletons is poorly understood. In this report, we investigated possible roles of BMP signaling in axial skeletal formation. First, we describe the expression patterns of BMP4 and type I receptors for BMP during somitogenesis in chick embryos based on whole mount in situ hybridization. Next, the effects of BMP on axial skeletal morphogenesis were investigated by implantation of BMP proteins into the dorsal mesoderm at the time of somitogenesis. Transcripts for both BMP4 ligand and its receptors are expressed in the dorsal ectoderm and mesoderm. Implantation of BMP4 and BMP2 into the dorsal regions of embryos result in subsequent anomalies of vertebrae, ribs, and scapulae. The effects of BMP implantation on the skeleton are shown to be dependent upon the somitic stage. Vertebral anomalies are restricted to the dorsolateral elements of the vertebrae and specifically observed after BMP implantation into embryonic day 2 (E2) embryos, but not E3 embryos. These results indicate that implantation of BMP into the dorsal part of embryos where endogenous BMP ligand and BMP receptors are expressed perturbs BMP signaling and causes axial skeletal malformations. The findings presented here suggest that BMP signaling may be involved in the early developmental process of the axial skeleton.

Spatial and temporal expression of the 5A11/HT7 antigen in the chick embryo : Association with morphogenetic events and tissue maturation.

The 5AII/HT7 antigen is the avian homologue of a 45-50X103 M r plasma membrane glycoprotein of the immunoglobulin super-gene family also identified in mammalian species (basigin, mouse gp42, MRC OX-47 antigen, M6 antigen). We had previously demonstrated that antibodies to this antigen interfere with heterotypic cell-to-cell interaction-dependent glial cell maturation in vitro. In this report, we sought to gain insight into its developmental role through an analysis of its distribution at various stages of avian embryogenesis. The primary mode of expression progresses from generalized staining of the undifferentiated tissue to intense labelling of specific cell types coincident with biochemical or morphological differentiation. In the retina, expression progresses from the generalized staining of the neural ectoderm, then, during neurogenesis, becomes restricted to Müller cells, photoreceptor cell bodies, the retina pigmented epithelium, the pigmented cells of the ciliary membrane and endothelia of the pecten. Similarly, the uniform staining of undifferentiated skin ectoderm progressively becomes confined to the germinative cells of the epidermis during biochemical differentiation of scutate and reticulate scales and formation of the feather follicle. During mesonephric and metanephric tubule development, labeling appears on those cells induced to form epithelia from the unlabeled mesenchyme and persists on the basal-lateral membranes of the convoluted tubules. Western blot analysis of NP-40 solubilized proteins from hatchling chicken identifies an immunoreactive polypeptide of 45-50X103 M r in tissues stained immunohistochemically and an additional band of 69X103 M r in the neural retina and pineal gland. The localization of the 5A11 antigen at boundaries typically associated with inductive interactions between cells and tissues suggests broad involvement in cell-to-cell interactions associated with cellular maturation.

Behavior of rabbit dental tissues in heterospecific association with embryonic quail ectoderm

The behavior of dental tissues from the rabbit, Oryctolagus cuniculus, in association with epithelium from the quail, Coturnix coturnix japonica, has been examined. Adult and embryo rabbits were employed in this study. Dental papillae from teeth at the cap stage from rabbit embryos and dental pulp from adult rabbits were isolated surgically and recombined with skin ectoderm from 72-hour-old quail embryos. The recombined tissues were cultured for 48 hours on semi-solid medium and subsequently removed and placed on chorio-allantoic membranes of 7-day-old chick embryos. Control cultures (dental pulp, dental papillae, and quail ectoderm) showed regression, atrophy, or differentiation according to the phenotype of the tissue. After 8 days in explant culture, heterologous recombinants composed of dental papillae and flank skin ectoderm from quail embryos developed differentiated chimeric tooth structures. It was unclear whether or not enamel was being secreted. The fact that the interactions between the enamel epithelium and the dental papillae are reciprocal is well known. The differentiation of odontoblasts can only occur in the presence of an enamel organ. Thus, the quail epithelium must have been induced to become an enamel organ, the lack of enamel proteins notwithstanding. Apical pulp and root pulp from adult rabbits plus quail ectoderm showed a high degree of regression and atrophy. At around 15 days of gestation, the rabbit dental papillae at the cap stage have already acquired odontogenic potential. By contrast, under the same experimental conditions, the dental pulp from continuous-growth teeth from adult rabbits did not show odontogenic potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Odontogenesis and amelogenesis in interacting lizard-quail tissue combinations.

In this study we examined the possible inductive role of the dental papilla from polyphyodont lizard tooth germs. Flank skin sheets of quail ectoderm enzymatically separated from dermal tissue were recombined with lizard tooth papillae and placed on semisolid medium and cultured for 2 days. Subsequently, the recombinants were removed and placed on the chorioallantoic membrane of chick hosts and incubated for 6 days. After this period of 8 days in explant, control tissues differentiated according to their own phenotypes. Lizard dental papilla alone differentiated as fibroblasts. Quail flank skin ectoderm differentiated into epithelial sheets. Intact lizard tooth buds developed into teeth with dentine and incipient enamel. In the best experimental recombinants, advanced and relatively well-constructed teeth were observed, with clear indications of hard tissue deposition in association with quail epithelium. The results show that mesenchyme of the adult lizard dental papilla and embryonic quail ectoderm of heterotopic origin are capable of carrying out the complex sequence of morphogenetic interactions involved in normal odontogenesis.

Ectodermal control of the avascular zone of the peripheral mesoderm in the chick embryo.

Prospective skin ectoderm is underlaid by a relatively thick (100 +/- 20 micrometer) avascular zone of mesoderm in most regions of the early embryo. To determine whether or not the ectoderm exercises a role in the establishment and maintenance of the avascular zone, trypsin-isolated pieces of backskin ectoderm from chick or quail embryos were implanted as a sheet into a slit cut deep into the capillary bed of the wing bud of host chick embryos of stages 19-23. In sham operations, slits were cut at various anteroposterior levels, and the wing was allowed to heal. At intervals of 3-48 hr after these operations, embryos were injected with India ink, fixed, and cleared. Implants formed flattened vesicles, usually in continuity with host ectoderm, but sometimes completely internalized. Periderm cells from each side of the vesicle faced each other, and the cells of the cuboidal layer faced an avascular mesodermal layer at least 100 micrometer thick at all points. The implantation of prospective skin ectoderm resulted in the formation of an avascular zone in normally vascularized mesoderm of the wing bud. In contrast, the vascular bed of the limb bud abutted directly on implants of Millipore filters or of Silastic silicone (Dow Corning). Likewise, the capillary bed came in direct contact with implants of retinal pigment epithelium, an ectodermal derivative normally in close contact with the vascular choroid coat of the eye. These results, taken in conjunction with earlier experiments that show the necessity of the apical ectodermal ridge for the formation of the marginal veins of the limb bud, suggest that epithelial-mesenchymal interactions are involved in important aspects of vasculogenesis in early embryos.

Tail (end) bud contributions to the posterior region of the chick embryo

AbstractChick tail buds labeled with tritiated thymidine were transplanted homotopically to unlabeled embryos to determine the specific body levels and structures formed by tail buds. In addition, labeling patterns of posterior structures were studied in normal embryos labeled for progressively longer time periods.Tail buds contributed labeled cells primarily to tail neural tube, somites, mesenchyme, and caudal arteries, but not to tail notochord, skin ectoderm, hindgut, or tail gut. Labeled somites were often located three to four somite levels anterior to labeled portions of neural tubes. In labeled normal embryos central notochordal cells were labeled only occasionally. This labeling pattern extended posteriorly into a region designated as prospective notochord, which merged posteriorly with the tail bud. The tail bud labeled uniformly and contained about the same density of labeled cells as the segmental plates, indicating that proliferation was not excessive in the former.Defects in operated embryos occurred primarily in the neural tube, somites, and notochord. The tail portion of the notochord, presumably formed from the prospective notochordal region, was never isolated from the trunk portion. The tail portion of the neural tube rarely seemed isolated from the trunk portion. Large, unpaired midline somites frequently developed. They appeared to form only when a space was available in which paired segmental plates could approach the midline and fuse.

人胎児腸管の発生学的研究

1. The pharyngeal pouches contact widely with the skin ectoderm and remain simple till the Streeter's horizon XV stage.2. During the next horizon XVI stage the contact areas becoming smaller surrounded by the mesenchymal mass form 3 pairs of small cervical vesicles corresponding to the 2nd, 3rd and 4th cervical grooves. The 4th cervical groove is the smallest and disappears during the XVI stage, while the 2nd and 3rd are visible in the next XVII stage passing away the former earlier, the latter the largest a little later.3. During these changes of the external forms the internal pharyngeal pouches begin to form the ductless glands. From the 3rd pouches begin to differentiate the parathyreoids 3 and the thymus, from the 4th the parathyreoids 4 and the lateral thyreoids. When these glands appear in form, these pouches are shut off from the cavity of the primive pharynx.4. This differentiation of these ductless glands indicates that it begins a little later than the Streeter's assertion. After the latter's description begins this differentiation in the XIV stage while our material late in the XVI.5. The oesophagus and trachea are embeded in the back body wall till our latest stage of XVIII, although the differentiation of the tissue is proceeding.6. As the stomach deviates to the left, there appears mesogastrium dorsale enclosing the cavity of the bursa omentalis with the dorso-caudal surface of the stomach. After Streeter the pouch for bursa omentalis appears in the horizon XII stage. In our material of the XIV stage the deviation of the stomach is so much advanced that the mesogastrium dorsale and ventrale are distinct.7. The mesoduodenum dorsale becomes evident as “Pancreaswulst” at the site of the dorsal mesentery continuous with the dorsal and ventral mesogastrium in the XVI stage, in which the site of the dorsal and ventral pancreas becomes definite dorsal to the duodenum. Its tissue is becoming massiv through the XVII to XVIII stage that at the latter stage it encloses the distal part of the duodenum close to the right side of the mesocolon.8. After Streeter a definitive mesentery beginning near the caudal end of the duodenum and extending downward to include the upper half of the colon can be spoken first in the XVI stage, but in our material a thin mesentery is visible already in the XIV stage without formation of a intestinal loop, the swelling of caecum also visible in this stage.9. The formation of a intestinal loop begins in the XV stage, which protrudes straight through XVI, XVII stages till about 3mm long, then appear in the XVIII stage curvatures at the cranial half of the loop. In the XVI stage begins the formation of the appendix.

Influence of Sex Hormones and Desoxycorticosterone on Melanophore Differentiation in Birds

Recently, it was found that explants of skin ectoderm from embryos of New Hampshire Red fowl occasionally yielded black melanophores, but red ones differentiated rarely, and a majority of the cultures were entirely negative. Since an examination of regenerating feathers from the adult (in which the plumage is predominantly red) showed that there was an abundance of red melanophores, it seemed desirable to find out what factors influence the differentiation of these pigment cells. The purpose of this report is to summarize some of the results which have been obtained by using sex hormones and a hormone of the adrenal cortex. In these experiments, a piece of skin was removed from the dorsal midline of a 6-day chick embryo (New Hampshire Red or Rhode Island Red) and divided into bilateral halves. One of these was explanted into a clot made up of embryonic extract mixed with plasma containing the sex hormone, and a control culture was made of the other half. Crystalline hormones were shaken up in blood plasma. Sesame oil, olive oil, and hormones dissolved in them were emulsified with plasma. Concentrations of hormones ranged from 20 to 300 γ per cc. Red melanophores differentiated in cultures treated with sex hormones within 24 to 48 hours, and were similar to those in the regenerating feathers of adult birds. They were slightly smaller than black melanophores, and contained sub-spherical, orange-red granules which partially dissolved in alcohol or xylol after the cells were fixed. The rapid, almost vibratory, movement of these granules within the living cell indicated that the cytoplasm must be extremely fluid. Black melanophores contained dark-brown or black, rod-shaped granules which moved very slowly in living cells and were insoluble in alcohol and xylol.

AMERICAN OTOLOGICAL SOCIETY

OTOLOGY ANDNEUROLOGY.Dr. J.GORDONWILSON, Chicago. This article will appear in full in a later issue. EARLYSTAGES IN THEDEVELOPMENT OF THEACOUSTICAPPARATUS IN THEHUMANEMBRYO.DR.GEORGEL.STREETER, Carnegie Laboratory of Embryology. Of the various sense organs the ear is the first to make its appearance in the human embryo. As the first somites begin to show, and before the closure of the neural tube, that part of the neural wall that is to furnish the acousticofacial ganglion exhibits an active proliferation of its cells, producing a lateral bulging. From the lateral surface of this fold the ganglion mass becomes detached by delamination. Coincident with this, an area of thickened skin ectoderm becomes demarcated as the otic plate. The progressive differentiation of this otic plate and its invagination and detachment from the surface ectoderm have been photographed and demonstrated in a series of twenty-four embryos, ranging from the stage of 7 somites to embryos 4 mm. long, at which time the otic vesicle