Growth and shaping of the fin and limb buds

The development of the fin and limb buds involves a balance of centrifugal (active) and centripetal (passive) mechanical forces, the first of which acts to move the walls of these structures away from each other and the second of which holds them together. When the volume of the mesodermal core increases, the generated force meets with the resistance of the basal membrane, and as a result, the limb bud has a tendency to acquire a cylindrical shape. Collagen fibers, individual mesenchymal cells, and their groups hold together the dorsal and the ventral wall of the limb bud, prevent the movement of these walls away from each other, and in this way direct bud growth along the proximodistal and the anteroposterior axes. The balance of the forces which stretch the ectodermal layer and those which constrain it has also been observed in the development of other body parts.     

Prophylactic and curative effects of Bacopa monniera in gastric ulcer models.

Bacopa monniera Wettst. (BM, syn. Herpestis monniera L; Scrophulariaceae), is an Ayurvedic drug used as a rasayana. Its fresh juice was earlier reported to have significant antiulcerogenic activity. In continuation, methanolic extract of BM (BME) standardized to bacoside-A content (percentage-38.0 ± 0.9), when given in the dose of 10–50 mg/kg, twice daily for 5 days, showed dose-dependent anti-ulcerogenic on various gastric ulcer models induced by ethanol, aspirin, 2 h cold restraint stress and 4 h pylorus ligation. BME in the dose of 20 mg/kg, given for 10 days, twice daily showed healing effects against 50% acetic acid-induced gastric ulcers. Further work was done to investigate the possible mechanisms of its action by studying its effect on various mucosal offensive acid-pepsin secretion and defensive factors like mucin secretion, mucosal cell shedding, cell proliferation and antioxidant activity in rats. BME 20 mg/kg showed no effect on acid-pepsin secretion, increased mucin secretion, while it decreased cell shedding with no effect on cell proliferation. BME showed significant antioxidant effect per se and in stressed animals. Thus, the gastric prophylactic and curative effects of BME may be due to its predominant effect on mucosal defensive factors.     

Germination ecology of drupelets of the fig (Ficus carica L.)

Abiotic and biotic factors and their effects on germination of fig drupelets were studied. The drupelets germinated between 10^oC and 30^oC.Constant humidity was necessary for germination and frequent drying out of the substrate was unfavourable. Total darkness for the whole duration of the experiments had a slighly negative effect on germination. The fastest germination occurred at constant humidity and an alternating temperature of 20/30^oC with exposure to light for 8 hours (at the higher temperature) and to darkness for 16 hours (at the lower temperature).Natural or artificial removal of drupelets from the syconium guaranteed a high germination percentage, whereas no germination occurred in drupelets left inside the syconium. Hence birds and mammals act as dispersal agents and mediators of germination. As they eat pieces of fig syconium, they free the drupelets from the flesh, eliminating the effect of inhibitors and/or microenvironments with high osmotic pressure inside the syconium. These findings support the hypothesis that germination occurs in autumn or spring depending on the climatic zone in which the species grows.     

Schwannoma-Derived Growth Factor Interacts with the Epidermal Growth Factor Receptor

Abstract: Schwannoma-derived growth factor (SDGF) is a potent mitogen and neuronal differentiation factor. Because of its relationship to epidermal growth factor (EGF) and the heregulins, it was asked if SDGF interacts with the EGF receptor or HER2/neu. SDGF binds to and causes the phosphorylation on tyrosine of the EGF receptor but not HER2/neu.     

Cytokine cross-talk between phagocytic cells and lymphocytes: Relevance for differentiation/activation of phagocytic cells and regulation of adaptive immunity

Cytokines represent one of the most important elements in the communication among different cell types. They play an increasingly better understood role in the communication among hematopoietic cells and in particular in the reciprocal regulation of effector cell types of innate or natural resistance (phagocytic cells and Natural Killer (NK) cells) and those of adaptive immunity (T and B lymphocytes). Lymphocytes produce several cytokines with either stimulatory (e.g., colony stimulatory factor) or suppressive (e.g., tumor necrosis factors and interferons) effects on proliferation of early hematopoietic cells. Many of these cytokines, alone or acting in synergistic combinations, also have a differentiation-inducing ability on immature myeloid cells and act as powerful potentiators of the cellular functions of terminally differentiated phagocytic cells. The communication between lymphocytes and phagocytic cells is not unidirectional, as phagocytic cells produce factors that regulate lymphocyte activation. In addition to their role as antigen presenting cells expressing costimulatory accessory molecules and secreting cytokines (e.g., IL-1, IL-6, TNF), phagocytic cells have been recently shown to produce Natural Killer cell Stimulatory Factor (NKSF/IL-12). IL-12 is a heterodimeric cytokine with important modulatory functions on cytotoxicity of NK and T cells, lymphocyte proliferation, lymphokine production, and development of T helper cell subsets. These communications between phagocytic cells and lymphocytes are further regulated by negative and positive feedback mechanisms that contribute to maintain the homeostasis of the system in physiologic conditions and to govern the changes in this equilibrium needed for the response to infectious or other foreign agents.     

Interactions of colonisation density and leaf environments on survival of Trioza eugeniae nymphs

1. Female eugenia psyllids Trioza eugeniae oviposit on the margins of expanding young Syzygium paniculatum leaves. The developing nymphs, feeding within pit‐shaped galls on the leaves, cause the leaves to become curled and deformed. The degree of leaf curling was correlated positively with densities of T. eugeniae nymphs. 2. High relative humidity increased persistence of nymphs on leaves at low insect densities, but persistence did not differ between high or low relative humidity conditions when nymphal densities were high and leaves were greatly curled. 3. Direct insolation increased nymphal mortality. Nymphs on the abaxial leaf surface in the direct sun had lower mortality than similarly exposed nymphs on the adaxial leaf surface. 4. Field populations showed high preference for abaxial leaf surfaces and a stronger preference for shaded adaxial surfaces than for exposed adaxial surfaces. 5. Adverse environmental conditions of direct insolation and low relative humidity may be mitigated by leaf curl associated with moderate populations, however competition at high nymphal density supersedes any potential benefit arising from leaf curling and has a negative effect on nymphal survival.     

Direct analysis of growth factor requirements for isolated human fetal hepatocytes

Summary Hepatocytes were isolated from human fetal liver in order to analyze the direct effects of growth factors and hormones on human hepatocyte proliferation and function. Mechanical fragmentation and then dissociation of fetal liver tissue with a collagenase/dispase mixture resulted in high yield and viability of hepatocytes. Hepatocytes were selected in arginine-free, ornithine-supplemented medium and defined by morphology, albumin production and ornithine uptake into cellular protein. A screen of over twenty growth factors, hormones, mitogenic agents and crude organ and cell extracts for effect on the stimulation of hepatocyte growth revealed that EGF, insulin, dexamethasone, and factors concentrated in bovine neural extract and hepatoma cell-conditioned medium supported attachment, maintenance and growth of hepatocytes on a collagen-coated substratum. The population of cells selected and defined as differentiated hepatocytes had a proliferative potential of about 4 cumulative population doublings. EGF and insulin synergistically stimulated DNA synthesis in the absence of other hormones and growth factors. Although neural extracts enhanced hepatocyte number, no effect on DNA synthesis of neural extracts or purified heparin-binding growth factors from neural extracts could be demonstrated in the absence or presence of defined hormones, hepatoma-conditioned medium or serum. Hepatoma cell-conditioned medium had the largest impact on both hepatocyte cell number and DNA synthesis under all conditions. Dialyzed serum protein (1 mg/ml) at 10 times higher protein concentration had a similar effect to hepatoma cell-conditioned medium (100 μg/ml). The results suggest that hepatoma cell conditioned medium may be a concentrated and less complicated source than serum for purification and characterization of additional normal hepatocyte growth factors. This work was supported by NIH grant DK35310. Editor’s statement Many investigators have struggled with the special problems associated with culture of differentiated hepatocytes. In this paper attention is given to the specific growth factor requirements for fetal human hepatocytes. The observation that factors from hepatoma conditioned medium or neural extracts enhanced the growth of the cells may indicate that additional growth factors are to be identified that are important in the survival and proliferation of hepatocytes, and may also indicate that the malignant transformation of these cells may involve the production of autocrine growth stimulators.     

Identification of tyrosine-phosphorylated colony-stimulating factor 1 (CSF-1) receptor and a 56-kilodalton protein phosphorylated in intact human cells in response to CSF-1

Colony-stimulating factor 1 (CSF-1) selectively supports the survival, proliferation, and maturation of hemopoietic cells of the monocyte/macrophage lineage. Although the cellular receptor for CSF-1, (the c-fms protein) is a protein-tyrosine kinase activated by the binding of CFS-1, the role of phosphorylation of cellular proteins in CSF-1 signal transduction is poorly understood. Therefore, we examined the CSF-1-stimulated phosphorylation of cellular proteins in human BeWo choriocarcinoma cell line (known to express the c-fms protein). BeWo cells were metabolically labeled with 32Pi, stimulated with recombinant human CSF-1, and extracted with detergent. Phosphotyrosyl proteins were isolated from detergent extracts by affinity chromatography on a highly specific antibody to phosphotyrosine. Rapid phosphorylation of 170-kd protein, followed closely by the phosphorylation of a 56-kd protein, was observed in response to CSF-1. The 170-kd phosphotyrosyl protein bound to wheat germ agglutinin and was secondarily immunoprecipitated with a specific anti-fms serum, consistent with its identity as the CSF-1 receptor. Although purified human macrophages that proliferate in culture in response to CSF-1 are not generally accessible, CSF-1 did stimulate the phosphorylation of a 56-kd protein in intact mononuclear leukocytes from human peripheral blood. Thus, the BeWo cell line may represent a good model for the study of CSF-1-stimulated cellular protein phosphorylation.