Flower wars

The role of competition in structuring plant communities has recently entered a new phase by considering interactions with pollinators. In this issue of Journal of Vegetation Science, Fantinato et al. show that co‐occurring grassland plants tend to use different pollinators or diverge in anther morphology. The study opens the door for investigation of the ecological and evolutionary processes that generate this pattern.     

Axonal Signals and Oligodendrocyte Differentiation

Axons produce signals that regulate oligodendrocyte proliferation, survival, terminal differentiation, and myelinogenesis. We review here recent in vitro and in vivo experimental approaches that aim to characterize axonal signals to oligodendroglia and to identify molecular mediators that regulate differentiation of oligodendendrocytes. We propose that the promoters of myelin genes, whose activation during terminal differentiation is modulated by axonal signals, can provide a means to identify molecular mediators of axo-oligodendroglial signals.     

Oligodendrocyte ablation impairs cerebellum development

Oligodendrocytes (OLs) are the glial cells of the central nervous system and are classically known to form myelin sheaths around most axons of higher vertebrates. Whether these cells might have other roles, in particular during development, has not been studied. Taking advantage of a transgenic mouse model in which OLs can be selectively killed in a desired time-frame, we have investigated the impact of OL ablation on cerebellar development. OL ablation was induced during the first 3 postnatal weeks, a time at which cerebellum development is ongoing. Strikingly, OL ablation triggers a profound perturbation of the known cerebellum developmental program, characterized by the disorganization of the cortical layers, abnormal foliation and a complete alteration of Purkinje cell dendritic arborization and axonal fasciculation. This phenotype is accompanied by decreased granule cell density, a disorganized Bergmann glia network and impaired migration of interneurons in the molecular layer. These results demonstrate a previously ignored role of OLs in the formation of the cerebellar cytoarchitecture.     

少突胶质细胞和视神经损伤

少突胶质细胞在中枢神经系统中具有重要和广泛的生理功能。视神经损伤后,出现髓鞘脱失、少突胶质细胞死亡和髓鞘再生等病理改变,产生的髓鞘碎片能抑制视神经轴索再生。少突胶质细胞的抑制特性由特定的抑制分子介导,目前已鉴定的抑制分子主要有Nogo、髓鞘相关糖蛋白（myelin—associated glycoprotein,MAG）、少突胶质细胞髓鞘糖蛋白（oligodendrocyte myelin glycoprotein,OMgp）等,它们通过同一受体复合体传导抑制信号。阻滞抑制分子及其受体,或调整神经元的内在生长状态以克服抑制分子的抑制作用,可以促进视神经损伤后再生。本文就这方面的进展作一综述。     

Derivation of Enriched Oligodendrocyte Cultures and Oligodendrocyte/Neuron Myelinating Co-cultures from Post-natal Murine Tissues

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications for understanding the pathogenesis of demyelinating diseases such as Multiple Sclerosis (MS). Cellular development is commonly studied with primary cell culture models. Primary cell culture facilitates the evaluation of a given cell type by providing a controlled environment, free of the extraneous variables that are present in vivo. While OL cultures derived from rats have provided a vast amount of insight into OL biology, similar efforts at establishing OL cultures from mice has been met with major obstacles. Developing methods to culture murine primary OLs is imperative in order to take advantage of the available transgenic mouse lines. Multiple methods for extraction of OPCs from rodent tissue have been described, ranging from neurosphere derivation, differential adhesion purification and immunopurification ^1-3. While many methods offer success, most require extensive culture times and/or costly equipment/reagents. To circumvent this, purifying OPCs from murine tissue with an adaptation of the method originally described by McCarthy & de Vellis ² is preferred. This method involves physically separating OPCs from a mixed glial culture derived from neonatal rodent cortices. The result is a purified OPC population that can be differentiated into an OL-enriched culture. This approach is appealing due to its relatively short culture time and the unnecessary requirement for growth factors or immunopanning antibodies. While exploring the mechanisms of OL development in a purified culture is informative, it does not provide the most physiologically relevant environment for assessing myelin sheath formation. Co-culturing OLs with neurons would lend insight into the molecular underpinnings regulating OL-mediated myelination of axons. For many OL/neuron co-culture studies, dorsal root ganglion neurons (DRGNs) have proven to be the neuron type of choice. They are ideal for co-culture with OLs due to their ease of extraction, minimal amount of contaminating cells, and formation of dense neurite beds. While studies using rat/mouse myelinating xenocultures have been published ^4-6, a method for the derivation of such OL/DRGN myelinating co-cultures from post-natal murine tissue has not been described. Here we present detailed methods on how to effectively produce such cultures, along with examples of expected results. These methods are useful for addressing questions relevant to OL development/myelinating function, and are useful tools in the field of neuroscience.     

Oligodendrocyte Precursor Cells Synthesize Neuromodulatory Factors

NG2 protein-expressing oligodendrocyte progenitor cells (OPC) are a persisting and major glial cell population in the adult mammalian brain. Direct synaptic innervation of OPC by neurons throughout the brain together with their ability to sense neuronal network activity raises the question of additional physiological roles of OPC, supplementary to generating myelinating oligodendrocytes. In this study we investigated whether OPC express neuromodulatory factors, typically synthesized by other CNS cell types. Our results show that OPC express two well-characterized neuromodulatory proteins: Prostaglandin D2 synthase (PTGDS) and neuronal Pentraxin 2 (Nptx2/Narp). Expression levels of the enzyme PTGDS are influenced in cultured OPC by the NG2 intracellular region which can be released by cleavage and localizes to glial nuclei upon transfection. Furthermore PTGDS mRNA levels are reduced in OPC from NG2-KO mouse brain compared to WT cells after isolation by cell sorting and direct analysis. These results show that OPC can contribute to the expression of these proteins within the CNS and suggest PTGDS expression as a downstream target of NG2 signaling.     

Taxes and the tobacco wars

In this issue (see pages 187 to 191) Dr. Vivian H. Hamilton and associates demonstrate that tax reductions introduced in 5 Canadian provinces in 1994 slowed the rate of decline in cigarette consumption in those jurisdictions. Although both reductions and increases in taxation have been shown to influence tobacco consumption, changes in smoking habits must also be understood in the context of battles being waged on other fronts in the tobacco wars. In addition, more finely detailed analyses are needed to determine the impact of taxation and other factors on the smoking habits of specific subgroups of the population, particularly teenagers.     

Cell wars fought with nanoweapons

We consider examples of the recently demonstrated means of attack and defense in the host versus cancer combat at the cellular level that involve interactions between widespread multifunctional proteins Tag7/PGRP-S, Hsp70, and Mts1/S100A4.     

Effects of Hypoxia on Oligodendrocyte Signal Transduction

Abstract: We have previously established that 21-day-old postnatal rat oligodendrocytes, maintained in monolayer culture and subjected to 6 h of hypoxia, show reversible inhibition of synthesis of α-hydroxy fatty acid and myelin basic protein but a dramatic induction of a 22-kDa protein, suggesting that this is a good model to study the mechanism of CNS demyelination caused by hypoxic injury. We now report that hypoxia also dramatically inhibits the basal protein kinase C-mediated phosphorylation of myelin basic protein and myelin 2',3'-cyclic nucleotide phosphohydrolase by 80%, but that the inhibition of phosphorylation can be reversed by addition of a protein kinase C activator, phorbol 12-myristate 13-acetate. The mechanism of action appears to involve the uncoupling of signal transduction at a site before phospholipase C, because hypoxia did not affect protein kinase C activity or its translocation to the membrane fraction. The most potent activator of phospholipase C (as measured by inositol phosphate release) was carbachol (muscarinic M₁ receptor agonist), followed by L-phenylephrine (α₁-adrenergic receptor agonist) in normal oligodendrocytes. Excitatory amino acids and histamine were ineffective. Hypoxia for 6 h completely inhibited both muscarinic and α₁-adrenergic receptor-mediated inositol monophosphate release but did not affect phospholipase D-coupled phosphatidylethanolamine production in response to carbachol. We therefore conclude from this and earlier work that early, reversible changes in oligodendrocytes metabolism result not simply from ATP depletion, but may specifically target GTP binding protein-mediated processes.     

A Low Repeat Length in Oligodendrocyte Chromatin

The behavior of oligodendrocyte chromatin after micrococcal nuclease digestion of nuclei was assayed in brains of rats of four different ages. During oligodendrocyte differentiation, a decreasing sensitivity of the chromatin to enzymatic attack was observed. On the other hand, the nucleosomal repeat length showed a slight tendency to increase during development. It is worth noting that even the highest values reported here for "oligodendrocyte" chromatin repeat lengths are significantly lower than 200 base pairs, the value previously reported by others for "non-astrocytic glia."     

Transient Transfection of Oligodendrocyte Progenitors by Electroporation

The transient transfection of transgenes into oligodendrocytes offers an important tool for studying the function of proteins during myelin formation. Currently established procedures, however, have generally resulted in low survival rates and low levels of uptake of the transgene into primary oligodendrocyte progenitors. We describe an electroporation method which yields transient transfection of oligodendrocyte progenitors of up to 10–15% of the surviving cells, and provides approximately 10⁴ surviving, transfected cells per electroporation reaction. In recent applications transgene expression persisted as the transfected progenitors progressed through subsequent stages of the oligodendrocyte lineage. This technique is expected to facilitate the study of the function of key proteins and lipids during the development of primary cultured oligodendrocytes.