Differential cell replication within the periosteum of the pig mandibular ramus.

The periosteum is anatomically and functionally divided into two layers. The inner osteoblastic layer contributes to local appositional bone growth. The outer fibroblastic layer receives the attachments of muscles and responds to bone growth by a more global enlargement. Coordinated growth of the layers could theoretically be produced by parallel replication rates in the layers followed by migration of fibroblastic layer cells. Alternatively, replication rates in the layers could differ, those in the osteoblastic layer reflecting local apposition and those in the fibroblastic layer responding to total bone growth. To test these alternatives, we compared two regions of the pig mandible, one appositional and one resorptive, equidistant from the major growth sites of the bone. Four 2-week-old pigs were injected i.p. with 5-bromo-2'-deoxyuridine (BrdU) to label replicating cells. Three hours subsequent to BrdU injection, animals were sacrificed. The mandibles were sectioned and processed immunocytochemically for BrdU. Periosteal cell mitotic activity was analyzed selectively at the level of the mandibular foramen on the medial and lateral ramal surfaces. The proportion of labeled cells was determined by grid-point analysis. Individual differences were minor but regional differences were striking. As expected, the osteoblastic layer of the lateral surface exhibited a greater proportion of mitotic cells than did the medial surface (p = 0.037). However, no such difference was seen in the fibroblastic layer, where medial and lateral sides exhibited identical replication activity. These results strongly support the second alternative, that cell division is differentially controlled in the two periosteal layers.

Effects of differentiation and transforming growth factor beta 1 on PTH/PTHrP receptor mRNA levels in MC3T3-E1 cells.

TGF beta has opposing effects on osteoblasts which are thought to be differentiation stage dependent; however, little is known concerning the effects of TGF beta on osteoblastic characteristics at different stages of maturation. The purpose of this study was to characterize the pattern of mRNA expression for the PTH/PTHrP receptor during normal osteoblastic differentiation in vitro, and evaluate the effects of TGF beta 1 on PTH/PTHrP receptor and osteocalcin (OCN) steady-state mRNA at different stages of osteoblastic differentiation. MC3T3-E1 preosteoblasts were plated at low density and induced to differentiate with ascorbic acid and beta-glycerophosphate. The first group served as a vehicle control and the remaining five groups received a single 48 h TGF beta 1 (3.0 ng/ml)-pulse staggered on a weekly basis for 30 days. Cell cultures were harvested weekly and evaluated for: steady-state PTH/PTHrP receptor and OCN mRNA levels via northern analysis, calcium and phosphorous levels, bone nodules via Von Kossa staining, alkaline phosphatase enzyme levels, and hydroxyproline levels. Group 1 (control) samples followed a normal pattern of proliferation, extracellular matrix deposition, and mineralization. PTH/PTHrP receptor and OCN mRNA expression increased 8-fold and 10-fold respectively, over the collection periods. When TGF beta 1 was administered during the first 48 h period (group 2) while cells were rapidly proliferating, there was a persistent inhibition of PTH/PTHrP receptor expression and a striking reduction in OCN mRNA expression at all time points. There was also a down-regulation of PTH/PTHrP receptor and OCN expression when TGF beta 1 was administered later during osteoblast differentiation (groups 3-6); however, these effects were not persistent. In addition there was a total lack of bone nodule formation in group two cultures, whereas groups 3-6 had increasing bone nodule formation because the TGF beta 1 was administered later in the culture period. These studies indicate that expression of the PTH/PTHrP receptor increases with osteoblastic differentiation and suggest that TGF beta 1 inhibits osteoblastic maturation with more persistent effects found in less differentiated osteoblastic cells.

Presence of osteonectin/SPARC in mandibular condylar cartilage of the rat.

Osteonectin/SPARC was most abundantly present in adherent osseous tissue of the cartilage explants. In cartilage explants with ossification fronts, it appears to be present in hypertrophic chondroblasts and in the mineralised extracellular cartilage matrix. In a number of cartilage explants it could be demonstrated in the fibroblastic cells of the perichondrium and, intra- and extracellularly, in cartilage located adjacent to the perichondrium. In young mandibular condylar cartilage (20 days post-conception up to 7 days of age) osteonectin/SPARC was characteristically present in the transitional zone, a small area of differentiating skeletoblasts. In cartilage, osteonectin/SPARC might play a role in the process of mineralisation and subsequent replacement by bone. It seems to be an important marker of skeletal differentiation processes.

Light and electron microscopy of the new born sagittal suture.

Morphogenesis and maturation of the sagittal suture in newborn C57B1/6J strain mice were studied using light and electron microscopy. Morphodifferentiation of the murine parietal bones progresses radially with the interposed sagittal suture, assuming a greater level of maturity at birth at a midpoint along its length. The presumptive suture develops in a sulcus, deeper posteriorly, more shallow anteriorly. Cells at the osteogenic front (OF) are distinguished from the surrounding fibrocytic cells by a number of distinctive characteristics: 1. increased cytoplasmic density; 2. extensive endoplasmic reticulum; 3. dispersed nuclear chromatin aggregates; 4. extensive surface projections; 5. close approximation. Mineralization of the developing parietal bone occurs extracellularly with the initial deposits of apatite crystals exhibiting no oriented relationship to either cellular or extracellular fibrillar elements. The majority of collagen fibers lie superior and inferior to the presumptive suture, oriented anteroposteriorly with their long axes parallel to the ectocranial surface. Other fiber bundles more intimately associated with the developing suture display a more random orientation.

Comparison of the offspring of three serial pregnancies during voluntary alcohol consumption in Sinclair (S-1) miniature swine.

The offspring of serial breedings of voluntary alcohol consuming Sinclair (S-1) miniature swine have been evaluated over the past three years. The first and second litters of 12 dams and the third litter of 6 dams were examined. All study animals had been consuming alcohol for at least 18 months prior to the first breeding. Alcohol consumption was continuous throughout the ninth study. Twelve non-alcohol-consuming sows were used as controls. The results of the study revealed a progressive decrease in mean litter size from controls of 6.66 in the control litters to 1.8 piglets per litter in the third litter born to alcohol-consuming dams. Perinatal deaths showed a progressive increase from 10% in the controls to 36.4% in the L3 litter. The birth weight showed a decline from a mean of 719 +/- 186 g in the control group to 467 +/- 122 g in the L3 litter. Abortions were not seen in control, first litter or second litter; however, there were 3 aborted fetuses in the third litter. Observation revealed no additional anomalies beyond the previous reports of anomalies seen in litters of alcohol-consuming S-1 miniature swine dams.

Clonorchiasis in New York City Chinese.

Among 150 Chinese-born residents of New York City a single stool examination showed 26% were infected with C, sinensis. Most of those infected were immigrants from the Kwangtung Province of China. The possibility of clonorchiasis in Oriental-born residents is emphasized.

Motility of the turtle embryo, Chelydra serpentina (Linné).

Periodic motility of turtle embryos was observed during their incubation periods (60 +/- 5 days). Cyclic activity was first observed between days 10 to 14; it increased to a peak level of 50 percent of the standard observation period on day 30 +/- 5, then declined to low levels until hatching activities were initiated. During the first third of the incubation period, motility of the turtles closely resembled that previously described for chick embryos at similar stages of development.