Microphase separation of living cells.

Self-organization of cells is central to a variety of biological systems and physical concepts of condensed matter have proven instrumental in deciphering some of their properties. Here we show that microphase separation, long studied in polymeric materials and other inert systems, has a natural counterpart in living cells. When placed below a millimetric film of liquid nutritive medium, a quasi two-dimensional, high-density population of Dictyostelium discoideum cells spontaneously assembles into compact domains. Their typical size of 100 µm is governed by a balance between competing interactions: an adhesion acting as a short-range attraction and promoting aggregation, and an effective long-range repulsion stemming from aerotaxis in near anoxic condition. Experimental data, a simple model and cell-based simulations all support this scenario. Our findings establish a generic mechanism for self-organization of living cells and highlight oxygen regulation as an emergent organizing principle for biological matter.

Cáncer de vejiga: tabaco como factor de riesgo / Bladder cancer: tobacco like risk factors

Entre setiembre de 1997 y marzo de 1998 se diagnosticaron y trataron en nuestro servicio 45 pacientes con cáncer de vejiga, de los cuales 41 casos fueron carcinomas superficiales, 3 infiltrantes y el restante carcinoma "in situ". El objetiv o del presente trabajo fue observar cuáles eran los factores de riesgo para el desarrollo de esta neoplasia. Se detectó que en el 85 por ciento de estos pacientes el hábito de fumar se encontraba presente (p<0,01), determinándose además la relación entre la cantidad de cigarrillos consumidos por día y el grado de diferenciación celular. Se registró también que los pacientes que fumaban tabaco negro desarrollaron tumores de mayor estadio de infiltración. En los restantes pacientes los factores de riesgo fueron labvorales (4 por ciento); hereditarios (2 por ciento); o dfesconocidos (9 por ciento)

Sonic hedgehog promotes the survival of specific CNS neuron populations and protects these cells from toxic insult In vitro.

Sonic hedgehog (Shh), an axis-determining secreted protein, is expressed during early vertebrate embryogenesis in the notochord and ventral neural tube. In this site it plays a role in the phenotypic specification of ventral neurons along the length of the CNS. For example, Shh induces the differentiation of motor neurons in the spinal cord and dopaminergic neurons in the midbrain. Shh expression, however, persists beyond this induction period, and we have asked whether the protein shows novel activities beyond phenotype specification. Using cultures derived from embryonic day 14.5 (E14. 5) rat ventral mesencephalon, we show that Shh is also trophic for dopaminergic neurons. Interestingly, Shh not only promotes dopaminergic neuron survival, but also promotes the survival of midbrain GABA-immunoreactive (GABA-ir) neurons. In cultures derived from the E15-16 striatum, Shh promotes the survival of GABA-ir interneurons to the exclusion of any other cell type. Cultures derived from E15-16 ventral spinal cord reveal that Shh is again trophic for interneurons, many of which are GABA-ir and some of which express the Lim-1/2 nuclear marker, but it does not appear to support motorneuron survival. Shh does not support the survival of sympathetic or dorsal root ganglion neurons. Finally, using the midbrain cultures, we show that in the presence of MPP+, a highly specific neurotoxin, Shh prevents dopaminergic neuron death that normally would have occurred. Thus Shh may have therapeutic value as a protective agent in neurodegenerative disease.

Bone morphogenetic proteins inhibit proliferation, induce reversible differentiation and prevent cell death in astrocyte lineage cells.

Bone Morphogenetic Proteins (BMPs) induce the differentiation of Serum-free Mouse Embryo (SFME) cells into astrocytes (D'Alessandro et al., 1994) as demonstrated by change in morphology, increase in Glial Fibrillary Acidic Protein (GFAP) content and classification as both type 1 and 2 astrocytes. Further analyses showed that in the presence of BMP, cells which had differentiated into astrocytes were inhibited from proliferation. Moreover, removal of BMP resulted in a resumption of proliferation accompanied by a loss of GFAP expression over time, indicating that under these in vitro conditions the differentiation was reversible. Since EGF is absolutely required for the survival of SFME cells, we examined the effect of its removal in the presence of BMP. Cell survival was > 80% in the presence of BMP-2, 7 or 2/7 and < 10% in the presence of TGF-beta 1. These data demonstrate that BMPs have effects on the proliferation, differentiation and survival of cells in the astrocyte lineage.

Bone morphogenetic proteins induce differentiation in astrocyte lineage cells.

Serum-free mouse embryo (SFME) cells express Glial Fibrillary Acidic Protein (GFAP), a specific marker of the astrocyte lineage, when treated with either Transforming Growth Factor Beta (TGF-beta) or calf serum. We examined the effects of the related Bone Morphogenetic Proteins (BMPs) which are expressed in the developing murine nervous system. Treatment with the heterodimers BMP-2/6 and 2/7 followed by the homodimers BMP-2, 4, 5, 6, and 7 induced higher levels of GFAP in these cells than either TGF-beta 1 or activin when tested at the same concentration. The BMP-induced cells resembled classically described astrocytes and were characterized by antibody markers as type 1 and type 2. In addition, these astrocytes also showed increased levels of the cell adhesion molecules CD44 and neural cell adhesion molecule (N-CAM), both known to be expressed by this cell type. These data clearly demonstrate that the BMPs function as differentiation factors as well as regulators of adhesion molecule expression for cells of the astrocyte lineage and suggest a key role in glial development in the nervous system.

Recombinant human bone morphogenetic protein induces bone formation.

We have purified and characterized active recombinant human bone morphogenetic protein (BMP) 2A. Implantation of the recombinant protein in rats showed that a single BMP can induce bone formation in vivo. A dose-response and time-course study using the rat ectopic bone formation assay revealed that implantation of 0.5-115 micrograms of partially purified recombinant human BMP-2A resulted in cartilage by day 7 and bone formation by day 14. The time at which bone formation occurred was dependent on the amount of BMP-2A implanted; at high doses bone formation could be observed at 5 days. The cartilage- and bone-inductive activity of the recombinant BMP-2A is histologically indistinguishable from that of bone extracts. Thus, recombinant BMP-2A has therapeutic potential to promote de novo bone formation in humans.

The affinity of cholesterol for phosphatidylcholine and sphingomyelin.

Erythrocyte ghosts were incubated with sonicated vesicles and the uptake of cholesterol by vesicles allowed to proceed to equilibrium. The experiments were carried out for a series of phospholipids at different temperatures. The equilibrium partition of cholesterol between ghosts and single shelled vesicles provided a measure of the relative affinities of cholesterol for the different phospholipids studied. It was found that the affinity of cholesterol for dipalmitoyl phosphatidylcholine was the same as that for N-palmitoyl sphingomyelin both at temperatures above and below the gel to liquid crystalline transition temperature of these phospholipids.

Characterization of mechanisms for transfer of cholesterol between human erythrocytes and plasma.

The removal from human erythrocytes of cholesterol (mass) and of [3H]cholesterol which had been introduced into the erythrocyte by exchange was studied. Removal was accomplished by incubating erythrocytes in plasma, the free cholesterol content of which had been lowered by the action of lecithin:cholesterol acyltransferase. It was shown that the exchange of cholesterol between erythrocytes and plasma and the net movement of cholesterol out of the membrane into plasma are characterized by the same rate constant and are driven by cholesterol to phospholipid ratios in cells and plasma. The apparent limitation on cholesterol depletion of erythrocytes observed in experiments of this type is explicable as the result of equilibrium between cholesterol in the membrane and in the plasma, an equilibrium reached when there is still cholesterol left in the cells. It is concluded from this study that all the exchangeable cholesterol in human erythrocytes is available for removal from the membrane.

[Neurosurgical aspects of fronto-ethmoidal osteomas; report of 6 cases and review of the literature]. / Aspectos neurocirrgicos dos osteomas fronto-etmoidais; relato de 6 casos e revisão da literatura.

The cases of six patients with fronto-ethmoidal osteomas which have produced intracranial complications are reported. The patients have been divided in two groups depending on their clinical aspects, from cranio-facial deformities to exophtalmus, rinorrhea, pneumocephalus, meningitis and mucocele. A review of the literature is made and the importance of such lesions is stressed together with a critical analysis of the methods proposed for their surgical treatment. The results obtained with a frontal approach and a plastic closure of the dura were uniformelly good with restoration of functions in all patients.

[Giant cell tumors of the sphenoid bone. Report of 3 cases and review of the literature]. / Tumores de celulas gigantes do esfenoide Relato de 3 casos e revisão da literatura

Three cases of giant cell tumor of the sphenoid bone are reported together with a revision of the previously reported cases in the neurosurgical literature. The importance of this tumor in the neurosurgical pathology is stressed, mainly to the impossibility of a correct diagnosis on a clinical and radiological basis. A good prognosis is possible with a least agressive surgery, transphenoidal biopsy and decompression, folowed by radiotherapy.