RESUMEN
Pattern formation is the developmental process that leads to the spatial ordering of cell differentiation. We have explored the problem of pattern formation in the development of the face of chick embryos. At early stages, the developing face consists of a series of small buds of tissue, the facial primordia that encircle the primitive mouth. The concepts of positional information provide a framework for considering how the patterns of differentiated cells are generated in the face. We suggest that the cranial neural crest cells must first be informed to which facial primordium they belong and then of their position within that primordium. The cells of the early primordia appear indistinguishable. However, when the mesenchyme cells are placed in high-density culture, cartilage differentiates. The extent and pattern of cartilage differentiation is characteristic for the cell population of each facial primordium. Myogenic cells also differentiate in the cultures, but the proportion of myogenic cells is independent of the extent of chondrogenesis. Within the facial primordia, a set of epithelial-mesenchymal interactions appears to be required for outgrowth and pattern formation along the proximodistal axis of the chick beaks. In culture, face epithelium locally inhibits cartilage differentiation and suggests that another set of epithelial-mesenchymal interactions may be involved in cell patterning. The mechanisms involved in specifying the mediolateral axis of the face, for example, the midpoint of the upper beak, are not known. Vitamin A derivatives, collectively known as retinoids, affect the development of the face of chick embryos and lead to a specific facial defect. Upper beak development is inhibited but the lower beak develops normally. The response to retinoids could be related to the specification of cells to belong to the facial primordium that will form the upper beak. Alternatively, retinoids may interfere with positional cues that operate to inform cells of their position within that primordium.
Asunto(s)
Cara/embriología , Cresta Neural/fisiología , Animales , Diferenciación Celular , Embrión de Pollo , Epitelio/fisiología , Cara/ultraestructura , Microscopía Electrónica , Retinoides/efectos adversosRESUMEN
The environmental contaminant cadmium (Cd) is a proven teratogenic agent in rodents. In hamsters, it causes craniofacial dysmorphogenesis. The underlying mechanism for this damage is unknown. Early facial development in hamsters occurs during gestation days 9-11 and involves the formation and appropriate fusion of several prominences surrounding the stomodeum. The hypothesis for this study is that the occurrence of Cd-induced facial defects involves a disruption of the normal formation and/or fusion of one or more of the facial prominences. Pregnant hamsters were treated with Cd (2 mg/kg) or water intravenously on gestation day 8 (8 A.M.). On gestation day 10 (8 A.M.) surviving embryos were processed to obtain scanning electron micrographs of the frontal view of the face. Measurements of the surface areas of 15 different portions of the face were obtained using a microcomputer equipped with a digitizer. Both qualitative and quantitative differences in the faces were detected upon comparing the Cd-exposed and control embryos. The surface areas of the prominences measured were significantly smaller in the Cd-exposed embryos. However the sizes of the other regions of the Cd-exposed faces were either little affected (nasal pit areas) or markedly increased (the interval of the face between the medial nasal prominences). Two possible explanations for these data are discussed.
Asunto(s)
Cadmio/toxicidad , Cara/anomalías , Teratógenos , Animales , Cricetinae , Cara/efectos de los fármacos , Cara/ultraestructura , Microscopía Electrónica de Rastreo , Valores de ReferenciaRESUMEN
Four patients received Zyderm collagen implant (ZCI) or Zyplast implant (ZI) in preauricular and infraauricular regions of facial skin periodically between one and nine months. Both materials were identified microscopically in the mid- to deep dermis at all points of the study and, in 60% to 70% of the injected sites, some material was also present subdermally. A slow, gradual colonization of ZCI by fibroblasts was noted compared with a delayed intense interaction of these cells with ZI. Also, there was some new collagen deposition associated with remodeling of the ZI, while no demonstrable synthetic activity occurred in relationship to ZCI. The results suggest that ZCI and ZI "migrate" deeper and eventually move into the subcutaneous plane. This movement could explain the loss of correction at six to nine months that is noted when this implant is used for age-related changes.
Asunto(s)
Envejecimiento/efectos de los fármacos , Aldehídos/efectos adversos , Colágeno/efectos adversos , Reactivos de Enlaces Cruzados/efectos adversos , Glutaral/efectos adversos , Prótesis e Implantes/efectos adversos , Piel/efectos de los fármacos , Procedimientos Quirúrgicos Dermatologicos , Cara/efectos de los fármacos , Cara/cirugía , Cara/ultraestructura , Femenino , Humanos , Masculino , Microscopía Electrónica , Persona de Mediana Edad , Proyectos Piloto , Cuidados Preoperatorios , Piel/ultraestructura , Factores de TiempoRESUMEN
Wrinkles in six aged persons (67-82 years of age) have been investigated by light microscopy (LM) and scanning electron microscopy (SEM). There are two types of wrinkles. One is a deep wrinkle which develops on the sun-exposed skin and does not disappear on stretching (permanent wrinkle). The LM and SEM showed less elastotic change in the upper dermis in the area of wrinkle than in that of the surroundings. The other type is a shallow wrinkle which develops on sun-protected skin and disappears on stretching (temporary wrinkle). The LM and SEM showed the decrease or loss of the elastic fibres in the papillary dermis as seen in ageing skin.
Asunto(s)
Envejecimiento , Piel/ultraestructura , Abdomen/ultraestructura , Anciano , Tejido Elástico/ultraestructura , Cara/ultraestructura , Femenino , Humanos , Masculino , Microscopía Electrónica de Rastreo , Cuello/ultraestructura , Piel/anatomía & histologíaRESUMEN
We examined temporal and spatial changes in the subepithelial mesenchymal cell process meshwork (CPM) in normally developing medial (MNP) and lateral nasal prominences (LNP) in mouse embryos by light and scanning electron microscopy. Marked changes were found only in the MNP during the fusion of the MNP and LNP. The CPM density in the prospective fusion area of the MNP gradually increased as the epithelial surfaces approached each other, attained its maximum just before contact, and decreased after contact. The CPM density in the prospective fusion area of the LNP changed only slightly even when the epithelial surfaces approached each other. The increase in CPM density paralleled that in the density of mesenchymal cell bodies. The LNP grew more actively toward the line of fusion than did the MNP during the progressive fusion of the two prominences. A larger number of fusion-associated epithelial morphological changes--the appearance of superficial protruding cells and cell degeneration--occurred in the MNP than in the LNP. These findings suggest that the increased CPM density is closely related to the growth of the facial prominences and the fusion-associated epithelial morphology and that the CPM plays an important role in the epithelial-mesenchymal interaction during the formation of the upper lip and primary palate.
Asunto(s)
Cara/embriología , Animales , Células Epiteliales , Epitelio/ultraestructura , Cara/citología , Cara/ultraestructura , Femenino , Edad Gestacional , Ratones , Ratones Endogámicos , Microscopía Electrónica , Microscopía Electrónica de Rastreo , Hueso Paladar/embriología , EmbarazoRESUMEN
Cleft lip with or without associated cleft palate [CL(P)], one of the most common human malformations, is in most cases, believed to be caused by a combination of genetic and environmental factors. Previous studies have shown that maternal respiratory hypoxia (10% O2) increases the incidence of CL(P) from the spontaneous level of 36% to 89% in CL/Fr mice. The current investigation was designed to study, morphologically, the developmental alterations of the primary palate primordia in CL/Fr embryos, following a reduction in maternal respiratory oxygen levels. Scanning electron microscopy was utilized to compare the development of 35-43 somite hypoxia and control (normoxia) embryos. Hypoxia increased the incidence of resorptions and increased the incidence of CL(P) in viable embryos, compared to normoxia. Debris, most of which was limited to the deeper aspects of the invaginating nasal placode, was present in hypoxia embryos at stages prior to primary palate fusion and was absent in comparably staged normoxia embryos. It is believed that this debris is cellular in nature and that associated retardation of placodal invagination is primarily responsible for the increased incidence of CL(P). Other effects on morphogenesis and/or growth retardation may also be contributing factors.
Asunto(s)
Labio Leporino/etiología , Hipoxia/fisiopatología , Animales , Desarrollo Embrionario y Fetal , Cara/embriología , Cara/ultraestructura , Ratones , Ratones Endogámicos , Microscopía Electrónica de Rastreo , MorfogénesisRESUMEN
The effects of excess retinol (vitamin A alcohol) on facial process formation were examined in cultured rat embryos. The embryos were explanted at day 11 of gestation (plug day = 0) and cultured for up to the 50-somite stage in rat serum containing added 1 microgram/ml or 10 micrograms/ml retinol. The reduction in outgrowth of facial processes was observed in 1-microgram/ml-retinol-treated embryos and this type of malformation was found to be more severe in 10-micrograms/ml-retinol-treated embryos. Histological findings of 10-micrograms/ml-retinol-treated embryos at the 50-somite stage showed that the nasal epithelium was developed but folded. In the mesenchyme, there were necrotic cells. Thymidine incorporation by mesenchymal cells of facial processes was determined. At the 50-somite stage, the uptake was decreased to 66.4% of control value at 1 microgram/ml retinol, whereas the addition of the same dose of retinol did not cause the inhibition at the 36-, 40-, and 42-somite stages. The uptake at the 50-somite stage was decreased to 23.0% as a result of the 10 micrograms/ml retinol treatment. Furthermore, the effects of cartilage-derived factor (CDF) on the facial mesenchyme were examined; 20 micrograms/ml of CDF stimulated the 3H-thymidine incorporation in facial mesenchyme, especially after the 42-somite stage. By the addition of 10 micrograms/ml retinol, the incorporation decreased to 45.7% at the 38-somite stage, but it did not decline with concomitant use of CDF after the 38-somite stage.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Anomalías Inducidas por Medicamentos , Vitamina A/toxicidad , Animales , Replicación del ADN/efectos de los fármacos , Embrión de Mamíferos , Cara/ultraestructura , Microscopía Electrónica de Rastreo , Técnicas de Cultivo de Órganos , RatasRESUMEN
The contact sites between the medial and lateral nasal processes during the period of facial formation of the mouse embryo were examined by light and electron microscopy. Characteristic superficial cells were observed at the transitional regions between the surface ectoderms and the nasal epithelia at the end of the isthmus, where the initial contact of the opposing nasal processes took place. At the later stage the contact sites extended to the bottom of the ravine formed by the two nasal processes, where the superficial cells always seemed to bridge the area between the nasal processes. These superficial cells had a large, clear nucleus and abundant cytoplasm as well as the common structural features characteristic of the embryonic cells. These cells were also observed on the surface near the contact site in the presumptive fusion area. These observations suggest that these superficial cells play a critical role in the epithelial adhesion of the medial and lateral nasal processes throughout the fusion.
Asunto(s)
Desarrollo Embrionario y Fetal , Cara/embriología , Animales , Cara/citología , Cara/ultraestructura , Ratones , Ratones Endogámicos ICR , Microscopía Electrónica de RastreoRESUMEN
The contact site between the medial nasal prominence (MNP) and the lateral nasal prominence (LNP) during the period of primary palate formation in the mouse embryo was examined by light and electron microscopy. Throughout this period, a distinctive type of superficial cell was observed at the contact site. These superficial cells had a large nucleus and abundant cytoplasm as well as structural features characteristic of embryonic cells. At earlier stages, these cells were seen at the transitional region between the surface ectoderm and the epithelia of the nasal pit at the end of the isthmus, where initial contact of opposing MNP and LNP took place. At later stages, these superficial cells appeared to bridge the gap between MNP and LNP at the contact sites, which extended to the bottom of the valley formed by MNP and LNP. These cells were also observed on the surface near the contact sites, that is, the presumptive fusion area. These superficial cells displayed well-developed junctional complexes (intermediate and gap junctions, and desmosomes). Many filaments were observed subjacent to the plasma membranes of these superficial cells, some of which were associated with junctional complexes. These observations suggest that this kind of distinctive superficial cell may play critical roles in the contact of MNP and LNP throughout the fusion process.