Oligosaccharide specificity of galectins: a search by frontal affinity chromatography.

Galectinomics: finding themes in complexity.

Coprinus cinereus has two main types of mycelia, the asexual monokaryon and the sexual dikaryon, formed by fusion of compatible monokaryons. Syngamy (plasmogamy) and karyogamy are spatially and temporally separated, which is typical for basidiomycetous fungi. This property of the dikaryon enables an easy exchange of nuclear partners in further dikaryotic-monokaryotic and dikaryotic-dikaryotic mycelial fusions. Fruiting bodies normally develop on the dikaryon, and the cytological process of fruiting-body development has been described in its principles. Within the specialized basidia, present within the gills of the fruiting bodies, karyogamy occurs in a synchronized manner. It is directly followed by meiosis and by the production of the meiotic basidiospores. The synchrony of karyogamy and meiosis has made the fungus a classical object to study meiotic cytology and recombination. Several genes involved in these processes have been identified. Both monokaryons and dikaryons can form multicellular resting bodies (sclerotia) and different types of mitotic spores, the small uninucleate aerial oidia, and, within submerged mycelium, the large thick-walled chlamydospores. The decision about whether a structure will be formed is made on the basis of environmental signals (light, temperature, humidity, and nutrients). Of the intrinsic factors that control development, the products of the two mating type loci are most important. Mutant complementation and PCR approaches identified further genes which possibly link the two mating-type pathways with each other and with nutritional regulation, for example with the cAMP signaling pathway. Among genes specifically expressed within the fruiting body are those for two galectins, β-galactoside binding lectins that probably act in hyphal aggregation. These genes serve as molecular markers to study development in wild-type and mutant strains. The isolation of genes for potential non-DNA methyltransferases, needed for tissue formation within the fruiting body, promises the discovery of new signaling pathways, possibly involving secondary fungal metabolites.

https://mmbr.asm.org/content/mmbr/64/2/316.full.pdf

Life History and Developmental Processes in the Basidiomycete Coprinus cinereus

Mushroom cultivation presents an economically important biotechnological industry that has markedly expanded all over the world in the past few decades. Mushrooms serve as delicacies for human consumption and as nutriceuticals, as "food that also cures". Mushrooms, the fruiting bodies of basidiomycetous fungi, contain substances of various kinds that are highly valued as medicines, flavourings and perfumes. Nevertheless, the biological potential of mushrooms is probably far from exploited. A major problem up to now is that only a few species can be induced to fruit in culture. Our current knowledge on the biological processes of fruiting body initiation and development is limited and arises mostly from studies of selected model organisms that are accessible to molecular genetics. A better understanding of the developmental processes underlying fruiting in these model organisms is expected to help mushroom cultivation of other basidiomycetes in the future.

Fruiting body production in Basidiomycetes.

Galectin-1 induces apoptosis of human thymocytes and activated T cells by an unknown mechanism. Apoptosis is a novel function for a mammalian lectin; moreover, given the ubiquitous distribution of the oligosaccharide ligand recognized by galectin-1, it is not clear how susceptibility to and signaling by galectin-1 is regulated. We have determined that galectin-1 binds to a restricted set of T cell surface glycoproteins, and that only CD45, CD43, and CD7 appear to directly participate in galectin-1-induced apoptosis. To determine whether these specific glycoproteins interact cooperatively or independently to deliver the galectin-1 death signal, we examined the cell surface localization of CD45, CD43, CD7, and CD3 after galectin-1 binding to human T cell lines and human thymocytes. We found that galectin-1 binding resulted in a dramatic redistribution of these glycoproteins into segregated membrane microdomains on the cell surface. CD45 and CD3 colocalized on large islands on apoptotic blebs protruding from the cell surface. These islands also included externalized phosphatidylserine. In addition, the exposure of phosphatidylserine on the surface of galectin-1-treated cells occurred very rapidly. CD7 and CD43 colocalized in small patches away from the membrane blebs, which excluded externalized phosphatidylserine. Receptor segregation was not seen on cells that did not die in response to galectin-1, including mature thymocytes, suggesting that spatial redistribution of receptors into specific microdomains is required for triggering apoptosis.

Stacy Charlton

Papers

Fungal galectins, sequence and specificity of two isolectins from Coprinus cinereus.