Gary R. Smiley

Fine structure of mouse embryonic palatal epithelium prior to and after midline fusion

Abstract The fine structure of the epithelium covering the medial aspect of the palatal shelves prior to fusion was studied in an attempt to elucidate the formation of the midline epithelial seam after fusion. Heads of embryonic C57BL mice were fixed in paraformaldehyde, and the mandibular process was removed. The palatal shelves were examined, and those palates which had only partly fused were microdissected out and post-fixed in osmium tetroxide. Ultrathin sections from the region just prior to fusion revealed that each palatal shelf had an epithelial covering approximately two to six cells thick, but soon after fusion the midline seam was reduced in thickness in some areas. Degenerative changes were noted along the epithelium covering the medial aspect of the palatal shelves before contact occurred. This epithelial degeneration occurred primarily in the superficial cells but was also observed in cells adjacent to the basal lamina. Their desquamation prior to fusion could account for the decreased thickness of the midline seam. No hemidesmosomes were observed and interruptions in the basal lamina did not appear to be directly associated with epithelial degeneration. Large electron-dense granules were observed in the epithelial cells prior to fusion and they became more numerous after fusion. The possible relationship of early epithelial degeneration and electron-dense granule formation to cleft palate formation is discussed.

Fine Structure of Mouse Secondary Palate Development In Vitro

Organ cultured homotypic palatal processes were studied with an electron microscope. Stages in the formation and breakdown of the midline epithelial seam through mesenchymal fusion are proposed to aid in studies of this aspect of secondary palatal development. In vitro palatal formation is similar to that observed in vivo.

Epithelial Changes in the Presumptive Regions of Fusion During Secondary Palate Formation

Specific epithelial changes before fusion of the palatal processes and nasal septum of human fetuses were studied at the fine structural level and were compared with the changes in rodents and chick cervical sinus formation.

Acid phosphatase in the Golgi apparatus of cells forming extracellular matrix of hard tissues

SummaryHistochemical studies using cryostat sections of fixed rodent fetal and newborn tissues indicated that acid phosphatase (APase) staining of the Golgi apparatus (GA) of cells secreting matrix for hard tissue formation was a general phenomenon. The enzyme was chiefly observed in the GA of tall secretory ameloblasts involved in enamel formation and in the GA of odontoblasts forming dentine; lysosome-like granules reactive for this enzyme were also observed in these cells. Activity was also intense in the GA and lysosomes of osteoblasts involved in intramembranous and endochondral bone formation.High levels of APase in the GA of extracellular matrix-forming cells appeared to correlate with secretory activity. The GA of most other cells, even chondroblasts forming cartilage matrix, had much less marked APase activity. Contrary to previous suggestions, it appears that APase may have a more direct role in osteogenesis than the osteolytic or resorptive action usually cited.

The role of the cartilaginous nasal septum in midfacial growth

Abstract 1. 1. The prenatal development of the cranial base and cartilaginous nasal septum in the midsagittal plane was investigated in normal A/Jax mice and A/Jax mice with spontaneous bilateral clefts of the lip and palate. 2. 2. The emergence of the snout as a prominent rodent characteristic coincided with the extension of the angulated cranial base and was most rapid prior to and during closure of the palatal shelves. 3. 3. There was no significant difference in the amount of extension of the cranial base between the normal fetuses and those with bilateral clefts of the lip and palate. Therefore, the amount of extension of the cranial base was not identified as the important etiologic factor in the formation of a cleft secondary palate in A/Jax mice with bilateral cleft lip. 4. 4. No morphologic or chronologic differences in development of the cranial base were detected between the normal and cleft fetuses. 5. 5. The cartilaginous nasal septum was significantly shorter in the fetuses with bilateral clefts of the lip and palate. This shortness appeared to be the result of a localized anteroposterior deficiency in the anterior third of the septal cartilage. 6. 6. This finding in cleft A/Jax fetuses does not support the view that the nasal septum acts as a “growth center” which set the pace for the downward and forward thrust of the midfacial skeleton during early facial growth.

In-vivo and in-vitro studies of the development of the avian secondary palate

Abstract The morphological characteristics of the epithelium of the chick-embryo palatal processes determined by light-, transmission- and scanning-electron microscopy demonstrated not only the proximity of the palatal processes during their development but also their failure to fuse, and the absence of medial palatal epithelial cell degeneration. There were numerous microvilli on the surface epithelial cells, and extensive and folded lateral cell membranes. In-vitro cultured expiants confirmed the absence of fusion of palatal processes despite the close proximity of the processes and the development of epithelial bridges linking them. The explants appeared to contract and indeed striated muscle was found in them, the sum of these observations confirming the view that the cleft avian palate may close during eating and drinking.

A histological study of the formation and development of the soft palate in mice and man

Abstract The secondary palate was examined to determine formation of the soft palate with regard to the process of merging and/or fusion. A midline seam of epithelium was observed in the region of the future soft palate, indicating that epithelial adherence and mesenchymal fusion was occurring, and not merging. Epithelial breakdown was more rapid and complete in the presumptive soft palate and along the junction of the nasal septum and palate than in the midline of the future hard palate. Based upon these observations and other studies, the hypothesis is proposed that the medial palatal epithelium is different and/or is acted upon differently in the anterior and posterior regions of the developing secondary palate.