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V M Diewert

Publications and source records attributed to V M Diewert.

At least 19 recordsLinked to original sources
PubMed1992

Recent advances in primary palate and midface morphogenesis research.

During the sixth week of human development, the primary palate develops as facial prominences enlarge around the nasal pits to form the premaxillary region. Growth of craniofacial components changes facial morphology and affects the extent of contact between the facial prominences. Our recent studies have focused on developing methods to analyze growth of the primary palate and the craniofacial complex to define morphological phases of normal development and to determine alterations leading to cleft lip malformation. Analysis of human embryos in the Carnegie Embryology Collection and mouse embryos of cleft lip and noncleft strains showed that human and mouse embryos have similar phases of primary palate development: first, an epithelial seam, the nasal fin, forms; then a mesenchymal bridge develops through the nasal fin and enlarges rapidly. A robust mesenchymal bridge must form between the facial prominences before advancing midfacial growth patterns tend to separate the facial components as the medial nasal region narrows and elongates, the nasal pits narrow, and the primary choanae (posterior nares) open posterior to the primary palate. In mouse strains with cleft lip gene, maxillary growth, nasal fin formation, and mesenchymal replacement of the nasal fin were all delayed compared with noncleft strains of mice. Successful primary palate formation involves a sequence of local cellular events that are closely timed with spatial changes associated with craniofacial growth that must occur within a critical developmental period.

Animals↗
PubMed1990

Morphological observations in normal primary palate and cleft lip embryos in the Kyoto collection.

Normal developmental events during human primary palate formation and alterations associated with cleft lip remain poorly defined. The purpose of this study was to analyze serially sectioned human embryos to identify morphological changes during normal palatal closure and alterations associated with failure of palatal formation. Normal and cleft embryos from the histological collection at the Congenital Anomaly Research Center at the University of Kyoto were studied and photographed for detailed evaluation. Seven serially sectioned cleft lip embryos of stages shortly after primary palate formation (Streeter-O'Rahilly stages 19, 20, and 22) with unilateral or bilateral clefts with varying degrees of clefting were studied. In the normal Kyoto embryos, initial nasal fin (epithelial seam) formation was observed between the medial nasal process and the lateral nasal and maxillary processes at stage 17. During stages 18 and 19, the nasal fin epithelium was replaced by an enlarging mesenchymal bridge, as the maxillary processes united with the medial nasal processes to form the primary palate. The most prominent features observed in the cleft embryos were a reduced thickness of mesenchymal bridging between the medial nasal and maxillary processes, with an excessive amount of epithelium at the junctions between these processes. With ingrowth of the maxillary processes, greater cell dispersion and apparent extracellular matrix accumulation were observed in the medial nasal region. During closure of the primary palate, terminal branches of the maxillary nerve crossed the mesenchymal bridge to the medial nasal region. The partial clefts had reduced maxillary ingrowth and smaller union areas with the medial nasal process. Detailed studies of experimental animal models are required to identify regional growth required for contact between the facial prominences, to clarify the mechanisms of mesenchymal ingrowth and epithelial displacement during palatal formation, and to identify local and/or general factors causing alterations that lead to primary palatal clefting.

Cleft Lip↗
PubMed1989

Developmental morphology of the solum nasi in the mouse lemur (Microcebus murinus).

The solum nasi of Microcebus murinus is characterized by the presence of a zona annularis, continuity between the anterior transverse lamina and the paraseptal cartilage, a continuous paraseptal cartilage, a palatine cartilage and a posterior transverse lamina. It lacks a fibula reuniens and possibly a cartilage of the nasopalatine duct as well as a palatine papillary cartilage. The morphology in M. murinus closely resembles that seen in Tupaia and Galago. This affinity results from the retention of primitive traits. However, Galago is reported to lack a zona annularis, thus displaying a specialization not shared with M. murinus. Therefore, the zona annularis provides a useful trait for distinguishing between the ontogenies of M. murinus and Galago.

Animals↗
PubMed1989

A computer graphics program for measuring two- and three-dimensional form change in developing craniofacial cartilages using finite element methods.

Allometric analysis of chondrocranial growth seeks to provide objective measures of morphogenetic form change during ontogeny of the primordial skull. Linear measures, typically employed to study differential growth, become problematic at the histological level since an external referencing system is impossible to achieve for microscopic anatomies in embryos. The purpose of this paper is to describe a computer graphics program which generates spatially invariant measures of two- and three-dimensional form change using finite element methods. Anatomical form change is viewed as a continuous deformation of an initial finite element representing an anatomical unit into a second configuration. The algorithm consists of isoparametric scaling of finite elements, strain matrix formulation, and size/shape variable derivation. The routine includes four segments serving to extract nodal data, generate the strain matrix relating the two morphologies as well as deriving corresponding size/shape variables, reference the major and minor axes of form change, and provide graphic display of the anatomical geometries. Applications are provided measuring two- and three-dimensional form change in the developing craniofacial cartilages of rats subjected to treatment with the known teratogen diazo-oxo-norleucine (DON). The finite element routine provides craniofacial form change variables which are expected in light of cellular alterations induced by DON administration. Finally, computational differences between this routine and similar approaches using finite element methods for analyzing biological form change are examined.

Animals↗
PubMed1988

The fate of Meckel's cartilage chondrocytes in ocular culture.

Modulation of the chondrocyte phenotype was observed in an organ culture system using Meckel's cartilage. First branchial arch cartilage was dissected from fetal rats of 16- and 17-day gestation. Perichondrium was mechanically removed, cartilage was split at the rostral process, and each half was grafted into the anterior chamber of an adult rat eye. The observed pattern of development in nonirradiated specimens was the following: hypertrophy of the rostral process and endochondral-type ossification, fibrous atrophy in the midsection, and mineralization of the malleus and incus. A change in matrix composition of the implanted cartilage was demonstrated with immunofluorescence staining for cartilage-specific proteoglycan (CSPG). After 15 days of culture, CSPG was found in the auricular process but not in the midsection or rostral process. In order to mark the implanted cells and follow their fate, cartilage was labeled in vitro with [3H]thymidine [3H]TdR). Immediately after labeling 20% of the chondrocytes contained [3H]TdR. After culturing for 5 days, 20% of the chondrocytes were still labeled and 10% of the osteogenic cells also contained radioactive label. The labeling index decreased in both cell types with increased duration of culture. Multinucleated clast-type cells did not contain label. Additional cartilages not labeled with [3H]TdR were exposed to between 20000 and 6000 rad of gamma irradiation before ocular implantation. Irradiated cartilage did not hypertrophy or form bone but a fibrous region developed in the midsection. Cells of the host animal were not induced to form bone around the irradiated cartilage. Our studies suggest that fully differentiated chondrocytes of Meckel's cartilage have the capacity to become osteocytes, osteoblasts, and fibroblasts.

Animals↗
PubMed1988

Surface modeling of craniofacial form in human embryos with a limited graphics terminal.

Three-dimensional morphology of the human embryo typically is visualized through computerized modeling techniques utilizing planar contours as the data base. Through this approach, tissue outlines are digitized, and contour lines are superimposed, providing a depth perspective. However, these techniques represent embryonic tissues as discontinuous surfaces and therefore ignore morphological information between sections. The purpose of this study was to develop a computerized routine for the three-dimensional surface modeling of craniofacial morphology in human embryos. Tissue outlines are digitized, thus converting contour information into x,y,z coordinate data. The three-dimensional reconstruction program BCSURF opens the data file and plots each tissue polygon. A center is determined for each contour, and this value is used to divide each polygon into four segments. Surface patches are generated by mapping each segment onto the corresponding segment of subsequent sections. A face table is constructed representing the surface patches and plane normals are generated for each patch. The normal and depth values are appended to the face table, and these measures determine the color intensity for each patch. Finally, patches are plotted providing a polygon mesh model, and each patch is filled with a dither pattern according to shading values. Three-dimensional reconstructions of the craniofacial region in Carnegie embryos (stages 15-17) are generated, and major morphological features are observed. Although bilevel shading capabilities cause discontinuous shading textures, this simple and inexpensive system can be easily upgraded for high-resolution graphics.

Computer Simulation↗
PubMed1987

An immunofluorescence study of chondrogenesis in murine mandibular ectomesenchyme.

The temporal and spatial distribution of type I collagen, type II collagen, cartilage-specific proteoglycan (CSPG) and fibronectin in mouse mandible is described. CD-1 mouse embryos of 12-, 15-, and 18-day gestation were used, and matrix molecules were localized using indirect immunofluorescence. On day 12, accumulation of type II collagen, CSPG, and fibronectin within regions of condensed mesenchyme was noted. On day 15, intense staining for type II collagen and CSPG occurred. Fibronectin was less brilliant with its greatest concentration near the perichondrium. On day 18, the cartilage matrix was undergoing osseous replacement concurrent with loss of type II collagen and CSPG. Type I collagen was seen in the perichondrium, membranous bone and sub-basement membrane region in specimens of all ages. Synthesis and expression of extracellular matrix molecules reflect patterns of differentiation in mandibular mesenchyme.

Animals↗
PubMed1986

Measuring histological form change with finite element methods: an application using diazo-oxo-norleucine (DON)-treated rats.

Analyses of drug-induced anatomical malformations routinely rely on linear measurements as a data base. Morphometric approaches utilizing these measures become inappropriate at the histological level at which a constant external referencing system is impossible to achieve. The purpose of this study was to quantify anatomical form change in the craniofacial region of late embryonic rats induced by a known teratogen, diazo-oxo-norleucine (DON), independent of any global referencing system. A sample of 17 untreated specimens of 17-day gestation served as the control. A second group, equivalent in number and age, received 2.0 mg DON on day 15. Homologous landmarks were identified in each specimen and craniofacial regions were partitioned with respect to these bounding nodes into nasal, oral, and mandibular elements. Form change was viewed as the continuous deformation of a reference craniofacial region from a 15-day untreated specimen into each final 17-day geometry. An interactive graphics program generated spatially invariant measures of form change through finite element methods. A local coordinate system was established for each element. A point within each region of the 15-day reference specimen was selected and the spatial relationship between this point and bounding nodes was quantified through interpolation functions. Size and shape variables were derived from a Lagrangian strain tensor, and values were compared between groups. Results showed that all three craniofacial regions were smaller in size among DON-treated specimens, but only oral and mandibular region shapes were different from controls. The finite element approach was considered superior to other histological morphometric techniques since an entire geometry was described and a visual description of form change as well as spatially invariant measures of size and shape change were derived.

Abnormalities, Drug-Induced↗
PubMed1986

Craniofacial growth during human secondary palate formation and potential relevance of experimental cleft palate observations.

Although formation of the secondary palate is known to involve a complex sequence of developmental events, current concepts of palatal clefting emphasize alterations in the palatal shelves. The objective of this study was to identify similarities in facial growth and palatal formation in man and in rodent experimental models and to examine mechanisms of experimentally induced cleft palate that might be relevant to human clefting. Morphometric analyses of facial growth changes reveal similar patterns of mandibular prominence, head extension, and increased oronasal cavity vertical dimension during secondary palate development, with more pronounced changes in the human. Experimental studies of induced cleft palate in rats and mice show that interference with growth changes can contribute to cleft palate. Failure of palatal shelves to make contact, often associated with delayed horizontal movement, has been observed with increased tongue obstruction secondarily to mandibular retrognathia after either growth inhibition in Meckel's cartilage or morphologic deformation of Meckel's cartilage. In other experiments, failure of adequate shelf contact has been observed with reduced shelf growth or with altered craniofacial relations associated with abnormally flexed head posture resulting from fetal growth abnormalities or oligohydramnios. The results of these studies show that the etiology of cleft palate malformation can be related to interference with a number of different development events not immediately in the palatal shelves. Similar alterations of craniofacial growth that affect the palate secondarily appear to be associated with etiology of cleft palate in human syndromes such as Pierre Robin syndrome and the oligohydramnios syndrome.

Animals↗
PubMed1986

A comparative study of development during primary palate formation in A/WySn, C57BL/6, and their F1 crosses.

Preliminary to a study comparing the morphological differences in facial growth of A/WySn (25% cleft lip) and C57BL/6 (0% cleft lip) mice, the growth and development of these strains and their reciprocal F1 hybrids was examined. Litters of these four populations were observed at D 10/8, D 10/20, D 11/8, and D 11/20 and scored for crown-rump length (CRL), somite number, and stage of facial development. Analysis of the data showed that, at any given gestational age, a hierarchy exists in which A/WySn is the smallest (based on CRL), has the fewest somites, and has the least-developed face. It is followed by the A/WySn-C57BL/6 (AC) cross, C57BL/6, and the C57BL/6-A/WySn (CA) cross, in order of increasing growth and development. The significant differences occurring between AC and CA indicate that maternal effects exist in A/WySn that retard the growth and development of its progeny. When the four populations were compared at similar facial stages, there was no significant difference between A/WySn and C57BL/6 in CRL or somite number. However, the hybrid populations tended to have significantly fewer somites and to be significantly larger than the parental populations at comparable stages of facial development. This suggests that, although somatic growth and development are coordinated with facial development in both cleft lip-susceptible and resistant strains, the association can be influenced by hybrid vigor. Thus, maternal effects do not appear to produce cleft lip through selective retardation of facial development in the purebred A/WySn. Nonetheless, these effects may still potentiate the expression of cleft lip.

Animals↗
PubMed1985

Development of human craniofacial morphology during the late embryonic and early fetal periods.

After formation of the primary palate during the fifth and sixth weeks postconception (PC), human facial morphology develops rapidly and by 10 weeks PC the face has a typically human appearance. The objective of this study was to review major growth changes associated with development of face shape during this period. Morphometric evaluation of staged human embryos and fetuses in the Carnegie Embryological Collection showed that between 7 and 10 weeks PC when crown-rump (CR) length increased from 18 to 49 mm, facial structures grew predominantly in the sagittal plane, with a four-fold increase in length, a two-fold increase in height, but little change in width. These growth changes altered relations of oronasal structures and at 8 weeks PC the palatal shelves elevated. The sagittal position of the maxilla and the mandible to the anterior cranial base increased by 25 degrees and 30 degrees, respectively, and the mandible was prognathic during secondary palate closure in the first 2 weeks of fetal development. Both the mean cranial base angulation--which remained unchanged at 128 degrees--and the achieved maxillary position of 84 degrees were similar to the angulations present later, prenatally and postnatally. Therefore, human patterns of cranial base angulation and maxillary position appear to develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the continuous craniofacial skeleton. The results suggest that rapid directional growth of the primary cartilages is important to development of normal human facial morphology and that interference with normal growth changes during this early critical period may produce irreversible effects on the face.

Cartilage↗
PubMed1985

Growth movements during prenatal development of human facial morphology.

After formation of the primary palate, human facial morphology develops rapidly and by 10-12 weeks pc the face has characteristics that appear typically human. The objective of this study was to review major growth movements and developmental changes in craniofacial tissues between 7 and 12 weeks pc. During this period (20 - 80 mm CR length), the upper and lower facial regions grow forward rapidly to achieve relationships to the cranial base that are similar to those present later prenatally and postnatally. Initial ossification of facial bones is present but the primary cartilages form the continuous craniofacial skeleton through the entire period. Rapid directional growth of the cartilaginous components between 7 and 10 weeks appears to be important to development of the typically human facial appearance prior to the formation of the continuous bony skeleton. The effects of altered primary cartilage growth on bony skeletal patterns were examined in experimental animal studies in which embryonic rats were exposed to teratogens. Reduction in the length of Meckel's cartilage or alteration in the shape of the cartilage was found to affect the size and shape of the bony mandible that developed later. Therefore, growth movements of the chondrocranium and Meckel's cartilage appear to play an important role in spatial relocation of developing facial bones during formation of craniofacial morphology. The results suggest that significant alterations in growth during this period when the primary cartilages form the continuous skeleton may produce significant irreversible effects on later prenatal and postnatal craniofacial morphology.

Animals↗
PubMed1979

Correlation between mandibular retrognathia and induction of cleft palate with 6-aminonicotinamide in the rat.

A single injection of the niacin antimetabolite 6-aminonicotinamide (6-AN) late in gestation produces cleft palate in the rat. In order to achieve an understanding of the mechanism of induction of cleft palate, craniofacial growth and palate development were studied in Sprague-Dawley rats after treatment with 6-AN on day 15 of gestation. The rats were maintained on a high niacin diet (95 ppm) and subjected to three different teratogenic levels of 6-AN. The first group was injected with 8 mg/kg, the second was fasted and injected with 8 mg/kg and the third was treated with 16 mg/kg. The lowest teratogenic dose, 8 mg/kg, produced mild mandibular retrognathia on day 16, delayed shelf elevation a few hours and resulted in small rostral and small caudal clefts of the secondary palate. The moderate dose, 8 mg/kg with fasting, produced more severe mandibular retrognathia, delayed shelf elevation about 24 hours and resulted in 37% full clefts and 63% partial clefts of the palate. The highest teratogenic dose, 16 mg/kg, produced severe mandibular retrognathia, delayed shelf elevation by more than 24 hours and resulted in 100% full clefts of the palate. In each 6-AN group, the most severe mandibular retrognathia was present between days 16 and 17, the critical time for palate closure in the rat. Treatment with 6-AN also produced abnormality of the epithelial cells of the palate, the toothbuds and the nasal septum. Molar and incisor toothbuds were small and malformed, and the epithelial surfaces of the palate and the soft tissue nasal septum did not fuse.

6-Aminonicotinamide↗
PubMed1979

Selective inhibition of mandibular growth and induction of cleft palate by diazo-oxo-norleucine (DON) in the rat.

A high percentage of cleft palates can be induced in rat fetuses by a single injection of the glutamine analog diazo-oxo-norleucine (DON) on day 15 of gestation. The purpose of this study was to evaluate the effects of DON in vivo on craniofacial growth and spatial relations in order to identify factors that may contribute to the palatal defects. Sprague-Dawley rats in the experimental groups were given a single IP injection of 2.0 mg DON (6 mg/kg maternal body weight) on day 15 and were killed on day 16 or 17. Control fetuses were collected on days 15, 16 and 17. Fetal heads were fixed in Bouin's solution, embedded in Paraplast and serially-sectioned. Midsagittal and coronal sections were projected at 30 X and a series of linear and angular measurements were made. DON had limited effect on growth of the cranial base, nasomaxillary complex, and palatine processes, but dramatically reduced the length of Meckel's cartilage. Treatment with DON delayed shelf elevation approximately 24 hours, and tongue position remained high in the oronasal cavity. Growth retardation in Meckel's cartilage therefore may contribute to delayed shelf movement by retarding downward and forward positioning of the tongue-mandibular complex.

Animals↗
PubMed1979

Palatal process movement in the rat as demonstrated in frozen sections.

During mammalian secondary palate development, movement of the lateral palatine processes from the vertical plane to the horizontal plane involves a complex interaction of the palatine processes and the tongue within a dynamic growing oronasal cavity environment. This study of pre-fixation facial profile photographs and frozen sections was undertaken to evaluate external and internal changes in the oronasal complex during secondary palate elevation without the shrinkage known to be present with routinhistological preparation of embryonic tissues. Frozen sections of Sprague-Dawley rat embryos between 15 and 17 days of (conceptual) age were prepared by hexane quenching and cryostat cutting. The results showed that, during the stages of palate development prior to shelf elevation, the tongue and mandible became positioned beneath the primary palate, and the vertical dimension of the oronasal cavity increased by the lifting of the nasomaxillary complex. The tongue and mandible maintained contact with the primary palate, whereas a space developed above the tongue in the middle and posterior palate regions. As the vertical dimension increased the volume of the palatomaxillary processes increased rapidly, the tongue became squeezed, and the palatine processes bulged medially above the level of the tongue. After shelf elevation extensive contact between the palatine processes was present, and the tongue became flattened. The results of this study support the observations of Lazzaro (1940) that rapid increase in shelf volume owing to increased intercellular volume contributes to movement of the processes above the tongue. But, rapid increase in shelf volume occurred contemporaneously with the time when the tongue and mandible outgrew the oronasal cavity and became positioned beneath the primary palate. Therefore, it would appear that the simultaneous occurrence of a lower and more forward tongue position, and an increased palatomaxillary process volume without change in maxillary width, contributed to the medial movement of the processes above the tongue.

Animals↗
PubMed1979

Experimental induction of premature movement of rat palatal shelves in vivo.

In order to enhance further knowledge of palatal shelf movement and the factors involved in palate closure, a method was developed for prematurely elevating palatal shelves in utero. Approximately 7 hours before expected shelf elevation, pregnant Sprague-Dawley rats were laparotomized and two medially directed squeezes were applied to the face of some of the embryos through the intact uterine wall. Palates from control (unsqueezed) and experimental animals were obtained immediately after the procedure and 2, 4, 7, 12 and 24 hours later. In the 0, 2 and 4 hours groups, 82% of experimental palates were elevated, whereas only 6% of control palates were elevated. At 0 hours only the hard palate in the experimental group had elevated, but at 2 and 4 hours almost half this group showed elevation of the soft palate as well, and, in addition, contact had been made between the elevated shelves.

Animals↗
PubMed1976

Graphic reconstructions of craniofacial structures during secondary palate development in rats.

Lateral and ventral graphic reconstructions of coronally sectioned rat fetuses at four stages of secondary palate development were made to illustrate the size, form, and spatial relations of craniofacial structures at each stage, and to indicate changes between stages. The results illustrated extensive changes in the nasomaxillary and tongue-mandibular complexes and spatial relations in the oronasal cavity during this 2-day period. During closure of the palate the palatine processes and molar dental laminae moved medially, the vertical dimension between the cranial base and Meckel's cartilage increased, and the Meckel's cartilage changed in shape from a "U" to a "V". During the 2-day period extensive increases in anteroposterior and vertical dimensions and limited changes in lateral dimensions resulted in a change in shape of the complete orofacial region. More extensive investigations, preferably quantitative, of the changes shown are indicated to identify the relative contribution of various craniofacial components and to establish the role of differential growth in secondary palate closure.

Animals↗