Calcium signalling and calcium channels in plants and yeast

Abstract

The concept of engineered extracellular matrices that can aid in the repair of damaged tissues is a common theme in the tissue engineering field. Central to this theme is the rationale that matrices, which mimic the composition and architecture of native tissues, can support and signal appropriate host cell repair responses. The design of such matrices draws upon concepts emerging from the cell biology, biomaterial and bioengineering fields. We have incorporated expertise from each of these areas into the development of matrices and matrix/growth factor combinations for the repair of bone and cartilage tissue using biomaterials such as type I collagen and hyaluronan. Type I collagen fibers coated with resorbable hydroxyapatite and crosslinked form an osteoconductive matrix that performs equivalent to autogenous bone when combined with a bone marrow aspirate or a recombinant human bone morphogenetic protein (GDF-5). The combination of recombinant human basic fibroblast grorth factor (FGF-2) with a hyaluronan gel results in a percutaneously injectable formulation that enhances fracture repair. More recent matrix formulations utilize a modified hyaluronan to coat and crosslink type I collagen fibers into a 3-D matrix that supports both osteogenesis and chondrogenesis in combination with growth factors such as GDF-5. The studies to be presented highlight the progress made in our understanding of cell, matrix, and growth factor interactions as they relate to skeletal tissue repair.Elevation of cytosolic free Ca plays a central role in transducing many metabolic and developmental stimuli in plants. Pathways for mobilisation of Ca from vacuoles include channels which are gated by inositol 1,4,5trisphosphate (IP3) and cyclic ADP-ribose (cADPR). By contrast much less is known about the properties of calcium-permable channels at the ER.We investigated the possibility that ligand-gated Ca release occurs in ERenriched vesicles derived from cauliflower inflorescences. cADPR-gated calcium release co-migrated with two ER markers, calnexin and antimycin A-insensitive NADH-cyt c reductase activity. Calcium release could also be evoked by the NADP metabolite nicotinic acid adenine dinucleotide phosphate (NAADP). This pathway, not previously described in plants, was insensitive to inhibitors of IP3-and cADPR-elicited calcium release, and, unlike the IP3-and cADPR-gated pathways, was located exclusively at the ER. Production of NAADP from N A D P by homogenates of cauliflower was detected using a sea urchin microsome bioassay. The existence of multiple Ca mobilisation pathways might contribute to the generation of stimulus-specific calcium signals in plants. In yeast, the alpha-factor induced mating response requires external C a and Ca uptake is mediated by interaction of two proteins. Cchl and Midl. The phenotype of deletion mutants suggest roles for these Ca channel forming subunits in a variety of additional physiological processes, including (1) cell viability at low Ca; (2) the adaptation of yeast growth to temperature; (3) th...