Involvement of an Extracellular Glucan Sheath during Degradation of Populus Wood by Phanerochaete chrysosporium

Observations by transmission electron microscopy of wood samples of Populus tremula inoculated with the white rot fungus Phanerochaete chrysosporium showed that, at certain stages of their growth cycle, hyphae were encapsulated by a sheath which seems to play an active role in the wood cell wall degradation. Chemical and immunochemical techniques and C nuclear magnetic resonance spectroscopy were applied to demonstrate the beta-1,3-1,6-d-glucan nature of the sheath. Double-staining methods revealed the interaction between the extracellular peroxidases involved in lignin degradation and the glucan mucilage. The glucan was also shown to establish a material junction between the fungus and the wood cell wall. It was concluded that, by means of these interactions, the sheath provides a transient junction between the hyphae and the wood, thus establishing a point of attachment to the site of the degradation. The association of peroxidases to the glucan matrix is in favor of the role of the sheath as a supporting structure. Furthermore, that the sheath was hydrolyzed during the attack demonstrated its active role both in providing the H(2)O(2) necessary to the action of peroxidases and in providing a mode of transport of the fungal enzymes to their substrates at the surface of the wood cell wall.     

The evolution of developmental strategy in marine invertebrates

Developmental mode varies widely in most animal phyla. These differences in developmental strategy exert a profound influence on the ecology and evolution of closely related species. The mechanistic alterations in ontogeny that lead to switches in developmental mode are coming under increasing scrutiny. Echinoids are one of the best-understood groups in this regard. Parallel modifications in direct-developing echinoids point to some of the key changes in oogenesis and embryogenesis that produce switches in developmental mode.     

Cryptic dioecy in flowering plants

In some dioecious plant species, mates and/or females have large and presumably costly opposite-sex structures that are sterile. This is termed 'cryptic dioecy'. Several new cases of cryptic dioecy have recently been studied. They may give information about the minimal requirements for the evolution of separate sexes from hermaphroditism, because the most important differences contributing to the initial advantage of the breeding system have not been obscured by further developments. Reviewed in this light, cryptic dioecy can provide evidence on the role of reallocation of reproductive resources in the evolution of dioecy.     

Tumour invasion: effects of cell adhesion and motility

Metastasis is the major cause of failure in cancer therapy. Recent studies of the molecular cell biology of the metastatic process have provided new insights into the mechanisms of cell-cell adhesion, cell-substrate adhesion and cell motility that underly invasion by tumour cells. In this review, Van Roy and Mareel discuss the role of proteins with invasion-promoting and invasion-suppressing functions in metastasis.     

Targeting and fusion in vesicular transport

Vesicular transport of proteins and lipids between distinct subcellular compartments is directly responsible for generating and maintaining the structure of the organelles of the secretory and endocytic pathways in eukaryotic cells. Rapid advances in a variety of experimental systems have resulted in the identification of molecules involved in late steps of the transport process. This article presents a general paradigm for vesicular fusion and reviews the available experimental evidence.     

Invariant chain--a regulator of antigen presentation

MHC class II molecules present internalized antigens to the immune system. They have long been known to associate with a polypeptide called the invariant chain. Recent findings have revealed that this polypeptide performs two functions. First, it prevents class II molecules from binding antigenic peptides at the site of synthesis of class II molecules in the endoplasmic reticulum.Second, it targets class II molecules to their destination in the endocytic pathway, where they pick up antigenic peptides derived from endocytosed antigens. Short sequences in the cytoplasmic portion of the invariant chain serve as subcellular address labels.The functions of the invariant chain help to explain how the immune system divides its defence against foreign pathogens between cytotoxic T cells and antibodies.