Nuclear morphometric analysis of osteoblast precursor cells in periodontal ligament, SL-3 rats

Experiments with osteoblasts cultured under varying orientations with respect to the gravity vector

Substrate attachment is crucial for normal growth and differentiation of many cell types. To better understand the role of gravity in osteoblast attachment and growth in vitro, 17-day-old embryonic chick calvarial osteoblasts were subjected to directional variations with respect to gravity. Osteoblasts, grown in MEM or DME supplemented with 10% FBS and attached to type I collagen-coated coverslips, were loaded into cylindrical containers completely filled with medium and oriented so that cells were either atop or beneath, or coverslips continuously rotated ( approximately 2 rpm) in a clinostat, thereby continuously changing their orientation with respect to gravity. Cells in these three conditions were collected daily for up to 6 days, and cell viability, two osteoblast functions, and proliferation were assessed. Data suggest the number and function of attached osteoblasts is unaltered by inversion or clino-rotation in initially confluent cultures. In sparsely plated cultures, however, osteoblast viability was significantly decreased ( approximately 50%) in inverted and rotated cultures during the first 3 days of sampling, but from days 4-6 no significant difference was found in viable cell number for the three conditions. Decreases in viable cell number within the first days of the experiments could result from death followed by detachment, detachment followed by death, differences in proliferation rate, or lag-phase duration. To help distinguish among these, BrdU labeling for 2 or 24 hr was used to assess cell proliferation rate. Log-phase growth rates were calculated and were unchanged among the three conditions tested. These results point to an increase in lag-phase duration in inverted and rotated cultures. In summary, changing the cell-substrate attachment direction with respect to gravity causes an immediate response in the form of diminished viable osteoblast number in sparse, early cultures, but the effect disappears after 3-4 days and does not occur in mature, confluent cultures.

Epibranchial placode-derived neurons produce BDNF required for early sensory neuron development

In mice, BDNF provided by the developing taste epithelium is required for gustatory neuron survival following target innervation. However, we find that expression of BDNF, as detected by BDNF-driven β-galactosidase, begins in the cranial ganglia before its expression in the central (hindbrain) or peripheral (taste papillae) targets of these sensory neurons, and before gustatory ganglion cells innervate either target. To test early BDNF function, we examined the ganglia of bdnf null mice before target innervation, and found that while initial neuron survival is unaltered, early neuron development is disrupted. In addition, fate mapping analysis in mice demonstrates that murine cranial ganglia arise from two embryonic populations, i.e., epibranchial placodes and neural crest, as has been described for these ganglia in non-mammalian vertebrates. Only placodal neurons produce BDNF, however, which indicates that prior to innervation, early ganglionic BDNF produced by placode-derived cells promotes gustatory neuron development.

Estimation of nuclear volume as an indicator of maturation of glial precursor cells in the developing rat spinal cord: a stereological approach

Studies on nuclear volume have shown that it is an indication of the state of differentiation of cells. This study provides evidence indicating increasing nuclear volume during cell maturation. Using unbiased stereological techniques, nuclear volume of both proliferating and non-proliferating glial cells was analysed in the developing spinal cord. Proliferating glial precursor cells were identified using a 5-bromo-2'-deoxyuridine (BrdU) incorporation assay. The nuclear volume of BrdU-labelled cells and unlabelled cells was determined in both periventricular regions and the white matter of the cord at different embryonic ages. In the periventricular region BrdU-labelled nuclei were smaller than unlabelled nuclei at all ages examined. These labelled cells represent dividing undifferentiated progenitors. The unlabelled neighbouring cells with larger nuclei represent a more differentiated population. In the white matter BrdU-labelled nuclei were of similar volume to the unlabelled nuclei. Both of these groups represent glial precursor cells that have migrated from deeper regions and are at similar stages of differentiation, perhaps with different proliferative potential. These findings indicate that the nuclear volume of early glial cells increases as these cells migrate and differentiate.