Biomedical subjects

V M Diewert

Publications and source records attributed to V M Diewert.

41 records · Page 3Linked to original sources

PubMedDate not supplied

Growth and morphogenesis of the human embryonic midface during primary palate formation analyzed in frontal sections.

Although it is recognized that morphology of the craniofacial complex changes during primary palate formation, little information is available about the sites and amounts of growth in different regions. The purpose of this study was to analyze growth patterns of human embryonic heads in frontal sections and to identify regional growth associated with changes in craniofacial morphology and formation of the primary palate. Photographs of frontal sections of 31 human embryos of stages 16 to 19 from the Carnegie Embryology Collection were selected at seven different planes through each head, enlarged and traced, and landmarks were located for computerized morphometric measurements and for finite element modeling (FEM) analyses. Anatomical form change from the initial geometry of the average early stage 16 group to that of later stages was shown by numerical values and graphic displays of regional growth changes during midfacial morphogenesis. Between stages 16 and 19, extensive changes in midfacial morphology occurred as the frontonasal prominence elongated vertically (height increased by seven times) and narrowed to approximately half the width, with more pronounced changes in the anterior nasal region. The brain and the face became vertically separated, and the facial prominences became more frontally positioned relative to the brain. Changes in depth of the face were very limited during this period. The area of the maxillary region increased extensively, particularly in the anterior region, as the maxillary prominences grew forward, lateral to the nasal cavity, to contribute to the primary palate. The lateral nasal prominences increased in size with a predominantly horizontal growth pattern. These patterns of vertical growth of the midfacial tissues, narrowing of the nasal pits and frontonasal prominence, forward growth of the maxilla, and relative separation of the brain and face were identified as predominant features of embryonic craniofacial growth during primary palate development.

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PubMedDate not supplied

Computer reconstructions of human embryonic craniofacial morphology showing changes in relations between the face and brain during primary palate formation.

During early development of the human facial region, the craniofacial complex undergoes extensive morphogenetic change. The purpose of this study was to generate computer reconstructions of serially-sectioned embryos in order to illustrate major changes in spatial relations that occur between cranial and facial tissues. Five human embryos of stages 16 to 18 from the Carnegie Embryology Collection, which were used in the frontal morphometric study, were selected to illustrate phases of morphogenesis. Serial photographs of frontal sections were enlarged, traced, and digitized for computer reconstruction. The craniofacial complex was divided into components that were similar to those analyzed in a morphometric study [Diewert VM, Lozanoff S: J Craniofac Genet Dev Biol 1993: 13:162-183] to facilitate visualization of changes in regional components. The major changes observed included changes in form of the brain and its ventral contour above the face; enlargement, elongation, and more ventral positioning of the facial prominences relative to the brain; and forward positioning of the eyes and facial tissues relative to cranial components. As the brain became separated from the face at advancing stages of development, the frontonasal prominences narrowed and became vertically elongated, the lateral nasal prominences enlarged and became medially positioned, and the maxillary prominences enlarged and extended anteriorly. Changes in cranial flexion and lifting up and back of the forebrain [Diewert VM, Lozanoff S: J Craniofac Genet Dev Biol 1993:13:184-192.] appear to contribute to withdrawal of the brain from between the facial prominences during early midfacial development before cartilaginous tissues of the chondrocranium develop.

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PubMedDate not supplied

A morphometric analysis of cell densities in facial prominences of the rhesus monkey embryo during primary palate formation.

The mechanisms by which the craniofacial complex undergoes morphogenetic change during primary palate formation remain unknown. Although changes in cell dispersion and extracellular matrix content are known to be involved in growth of embryonic primordia, little information about these parameters is available for the mammalian face. The purpose of this study was to analyze cell densities in different facial regions of rhesus embryos during primary palate formation. Eight serially-sectioned embryos of stages 13 to 18 in the collection at the California Primary Research Center, most labeled with 3H-thymidine, were analyzed by making regional cell counts at x400 with an ocular micrometer. Three embryos with autoradiographic label preserved in every section were used to analyze patterns of labeling through the depth of the entire face. The results showed that different regions of an embryonic face have significantly different cell densities. At the early stages, the cell densities were high in the maxillary prominences, and the lateral and medial nasal prominences; whereas cell densities were low in midline tissues. At later stages, cell densities were lower in the lateral portion of the maxillary prominences than in the nasal prominences. Serial counts through the face showed regional variation in individual prominences, but central high-density cores did not appear to be present. Labeling with 3H-thymidine was present in all facial primordia. Labeling indices were consistently higher in facial prominences than in midline tissues ventral to the brain. The results suggest that regional changes in cell densities could be used to reflect net changes in cell dispersion associated with altered balances between cell proliferation and extracellular matrix content in embryonic facial primordia.

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PubMedDate not supplied

Deficient and delayed primary palatal fusion and mesenchymal bridge formation in cleft lip-liable strains of mice.

During mammalian primary palate formation, the facial prominences enlarge around the nasal pit, fuse and then merge to give rise to the tissue of the upper lip and premaxillary region. The mechanisms involved in successful primary palate formation and how they are affected in the cleft lip genotype remain poorly understood. The purpose of this study was to compare morphometrically internal development and growth of the primary palate in five different strains of mice. Two of the strains, BALB/cByJ, and C57BL/6J, have normal primary palate development, and three of the strains, A/J, A/WySn, and CL/Fr, have stable frequencies of cleft lip associated with genotype. In the present study, frequencies of 4, 23, and 24%, respectively, were observed on day 13. For palatal growth analysis, embryos were collected on days 10 and 11, staged by number of tail somites (TS), and the heads were photographed and serially sectioned for measurement of primary palate components. The heights of the epithelial seam and the mesenchyme bridge between the facial prominences were measured on serial sections and areas of contact were calculated. The position or depth of the maxillary prominence was determined from the number of frontal sections from its tip to the rostral end of the nasal fin. Analysis of measurements showed that in cleft lip strains enlargement of the epithelial seam and replacement of epithelia by a mesenchymal bridge were both delayed relative to somite stages. Measurements from day 11 embryos with complete failure of contact were excluded from the growth analyses. The mesenchymal bridge formed at 12--13 TS in noncleft strains, 14 TS in the A/J strains with higher cleft lip frequency, and 15--17 TS in A/WySn and CL/Fr strains with higher cleft lip frequency. Forward growth of the maxillary prominence was highly correlated with the primary palate measurements and mesenchymal bridge formation in all strains. In both cleft and noncleft strains, the primitive choanae open at 18--20 TS and the medial nasal region narrows with advancing embryonic development. As a result, cleft lip-liable strains have a narrower window in development in which a robust mesenchymal bridge must form, thus increasing the liability to cleft lip.

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PubMedDate not supplied

Distribution of basement membrane components in the mouse primary palate.

Laminin, type IV collagen, and fibronectin are major components of the basement membrane of epithelial tissues. The purpose of this study was to characterize their distributions as the epithelial seam of the primary palate is disrupted and the mesenchymal bridge forms and enlarges. The distributions of these molecules were studied with indirect immunofluorescence in day 11 (9-20 tail somites), noncleft CD1 mice. During epithelial seam formation at 9-11 tail somites (TS), all three molecules were intensely localized in the basement membrane of the seam and adjacent stomodeal and nasal epithelia. During epithelial seam replacement by mesenchymal tissues at 12-18 TS, basement membrane components were first fragmented along the seam, then absent at the site of the mesenchymal bridge. At 19-20 TS, basement membrane components were intact around the margins of the primary palate. These results show that disruption of basement membrane components occurs rapidly and simultaneously with mesenchymal bridge formation in the primary palate.

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