BODIPY dyes and their derivatives: syntheses and spectroscopic properties.

/pdf/functional-nucleic-acid-sensors-k8tlieshyr.pdf

Functional Nucleic Acid Sensors

Grasping objects: the cortical mechanisms of visuomotor transformation

Nerve growth factor (NGF) was discovered 50 years ago as a molecule that promoted the survival and differentiation of sensory and sympathetic neurons. Its roles in neural development have been characterized extensively, but recent findings point to an unexpected diversity of NGF actions and indicate that developmental effects are only one aspect of the biology of NGF. This article considers expanded roles for NGF that are associated with the dynamically regulated production of NGF and its receptors that begins in development, extends throughout adult life and aging, and involves a surprising variety of neurons, glia, and nonneural cells. Particular attention is given to a growing body of evidence that suggests that among other roles, endogenous NGF signaling subserves neuroprotective and repair functions. The analysis points to many interesting unanswered questions and to the potential for continuing research on NGF to substantially enhance our understanding of the mechanisms and treatment of neurological disorders.

Nerve growth factor signaling, neuroprotection, and neural repair

http://www.bio21.bas.bg/ibf/PC_review.pdf

Phases and phase transitions of the phosphatidylcholines

We have examined the phase partition preferences of the even chain length (n = 10-22) diacyl-3'3'-indocarbo-cyanine iodides (Cn diI) incorporated in disaturated lecithin (PC) vesicles. Two parameters were used to determine this phase preference: (i) the direction of shift of the phase transition temperature (Tm) induced by the dyes and (ii) the self-quenching of fluorescence due to aggregation in the gel phase of those dyes which preferentially partition into the fluid. Dyes that lower Tm preferentially partition into the fluid phase; those that raise Tm preferentially partition into the gel. By these criteria in dimyristoyl-PC, C10 diI and C12 diI preferentially partition into the fluid phase, C14 diI and C16 diI show no preferential partition, C18 diI preferentially partitions into the gel, and C20 diI and C22 diI preferentially partition into the fluid. In dipalmitoyl-PC, the pattern of preference is identical with that observed in dimyristoyl-PC, only shifted to longer chain length diI's by two carbons. Diffusion measurements by fluorescence photobleaching recovery of these dyes in gel-phase multilayers showed tham all to be immobile, D less than 10(-10) cm2/s, while in fluid-phase multilayers thay all had diffusion coefficients of D approximately 10(-8) cm2/s independent of chain length. In mixed-phase multilayers, however, each Cn diI showed mobile fraction which reflected its phase-partition preference.

Selectivity of fluorescent lipid analogs for lipid domains

We measured the nonradiative fluorescence resonance energy transfer between 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD) labeled lipids (amine labeled phosphatidylethanolamine or acyl chain labeled phosphatidylcholine) and rhodamine labeled lipids in large unilamellar dioleoylphosphatidylcholine vesicles. Two new rhodamine labeled lipid analogues, one a derivative of monolauroylphosphatidylethanolamine and the other of sphingosylphosphorylcholine, were found to exchange through the aqueous phase between vesicle populations but not to be capable of rapid transbilayer movement between leaflets. Energy transfer from NBD to rhodamine was measured using liposomes with symmetric or asymmetric distributions of these new rhodamine labeled lipid analogues to determine the relative contributions of energy transfer between donor and acceptor fluorophores in the same (cis) and opposite (trans) leaflets. Since the characteristic R0 values for energy transfer ranged from 47 to 73 A in all cases, significant contributions from both cis and trans energy transfer were observed. Therefore, neither of these probes acts strictly as a half-bilayer quencher of NBD lipid fluorescence. The dependence of transfer efficiency on acceptor density was fitted to a theoretical treatment of energy transfer to determine the distances of closest approach for cis and trans transfer. These parameters set limits on the positions of the fluorescent groups relative to the bilayer center, 20-31 A for NBD and 31-55 A for rhodamine, and provide a basis for future use of these analogues in measurements of transbilayer distribution and transport.

Determination of the transbilayer distribution of fluorescent lipid analogues by nonradiative fluorescence resonance energy transfer.

Interaction with TrkA immobilizes gp75 in the high affinity nerve growth factor receptor complex.

We have found that 2,4,6-trinitrobenzenesulfonate (TNBS) is an effective quencher of the fluorescence of the 1,1'-dialkyl-3,3,3',3'-tetramethylindocarbocyanines (CNdiI's). This quenching appears to occur by complex formation rather than a collisional mechanism. By use of this quenching, we have studied the transbilayer asymmetry of CNdiI labeling for large unilamellar membranes of egg phosphatidylcholine and the plasma membranes of human red blood cells and of ram epididymal spermatozoa. When CNdiI is added to membranes by ethanolic injection, only the outer leaflet labels. We have further shown that in large unilamellar vesicles of egg phosphatidylcholine, the CNdiI's do not appreciably "flip-flop" to the inner leaflet for at least 4 h at temperatures between 4 and 37 degrees C.

Determination of the sidedness of carbocyanine dye labeling of membranes.

Mammalian sperm plasma membranes, in contrast to those of mammalian somatic cells, exhibit a significant fraction of lipid that does not diffuse laterally in the plane of the membrane. This nondiffusing fraction results from lipid-lipid interactions. Similar nondiffusing fractions are found in mixed-lipid model systems that contain coexistent gel and fluid domains. These results suggest that the sperm plasma membrane may also exhibit lateral phase segregations of lipids and may contain significant amounts of gel-phase lipid. In this paper we use differential scanning calorimetry to show that, in contrast to the plasma membranes of mammalian somatic cells, the plasma membrane from the anterior region of the head of ram sperm exhibits at least two major endothermic transitions, one centered at approximately 26 degrees C and one centered at approximately 60 degrees C. The heats of these transitions are consistent with gel-to-fluid transitions in model membranes. These transitions are observed both in plasma membrane vesicles and in rehydrated lipid extracts made from these vesicles. These results demonstrate that at physiological temperatures the lipids of the ram sperm plasma membrane are segregated into coexistent fluid and gel domains. Since sperm encounter a wide range of temperatures during their development, these phase transitions may be important in establishing dynamic domains of lipid requisite for epididymal storage and fertilization.

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David E. Wolf

Papers

Selectivity of fluorescent lipid analogs for lipid domains

Determination of the transbilayer distribution of fluorescent lipid analogues by nonradiative fluorescence resonance energy transfer.

Interaction with TrkA immobilizes gp75 in the high affinity nerve growth factor receptor complex.

Determination of the sidedness of carbocyanine dye labeling of membranes.

Lipid domains in the ram sperm plasma membrane demonstrated by differential scanning calorimetry