Cleavage of cartilage oligomeric matrix protein (thrombospondin-5) by matrix metalloproteinases and a disintegrin and metalloproteinase with thrombospondin motifs.

Cartilage oligomeric matrix protein (COMP) is a pentameric glycoprotein present in cartilage, tendon and ligament. Fragments of the molecule are present in the diseased cartilage, synovial fluid and serum of patients with knee injuries, osteoarthritis and rheumatoid arthritis. Although COMP is a substrate for several matrix metalloproteinases (MMPs), the enzymes responsible for COMP degradation in vivo have yet to be identified. In this study we utilised well-established bovine cartilage culture models to examine IL-1alpha-stimulated COMP proteolysis in the presence and absence of MMP inhibitors. COMP was released from bovine nasal cartilage, in response to IL-1alpha, at an intermediate time between proteoglycans and type II collagen, when soluble MMP levels in the culture medium were undetectable. The major fragment of COMP released following IL-1alpha-stimulation migrated with an apparent molecular mass of approximately 110 kDa (Fragment-110) and co-migrated with both the major fragment present in human arthritic synovial fluid samples and the product of COMP cleavage by purified MMP-9. However, the broad-spectrum MMP and ADAM inhibitor BB94 only partially inhibited the formation of Fragment-110 and failed to inhibit COMP release significantly. Therefore the results of these studies indicate a role for proteinases other than MMPs in the degradation of COMP in bovine cartilage. It was further demonstrated that purified COMP was cleaved by ADAMTS-4, but not ADAMTS-1 or -5, to yield a fragment which co-migrated with Fragment-110. Therefore this is the first demonstration of COMP as a substrate for ADAMTS-4, although it remains to be determined whether this enzyme plays a role in COMP degradation in vivo.     

Plant cell cycle: cellularisation of the endoderm needs spätzle

Early development of the endosperm of flowering plants involves the formation of a syncytium through successive rounds of nuclear division without cell wall synthesis. New data reveal that cellularisation of this syncytium requires the SPATZLE protein and involves the formation of cell walls similar to those of somatic tissues.     

Expression and post-translational processing of gastrin in heterologous endocrine cells

The biosynthesis of gastrin involves a complex series of post-translational processing reactions that result in the formation of a biologically active secretory product. To study the mechanisms for two specific reactions in gastrin processing, namely dibasic cleavage and amidation, we infected AtT-20, GH3, and Rin5-f cells with the retroviral expression vector, pZip-NeoSV(X), containing human gastrin cDNA. We detected gastrin and its glycine extended post-translational processing intermediates (G-gly) in the media and cell extracts of successfully infected cells. Characterization of the molecular forms of gastrin in these cell lines revealed that GH3 and Rin5-f processed gastrin in a manner similar to antral G-cells but the cleavage of the Lys74-Lys75 bond that converts G34 to G17 appeared to be suppressed in AtT-20 cells. Even after conversion of this site to Arg74-Arg75 via site-directed mutagenesis, the At-20 cells synthesized G34 predominantly. All of the infected cells amidated gastrin but the gastrin/G-gly ratio, a reflection of amidation within the cells, was enhanced in GH3 and Rin5-f cells but diminished in AtT-20 cells upon treatment with dexamethasone (10(-4) M) for 3 days. The dibasic cleavage of gastrin was uneffected by dexamethasone. Our data suggest that the activities of post-translational processing reactions responsible for the synthesis of biologically active gastrin exhibit considerable tissue and substrate specificity.     

Variation and response to experimental warming in a New Zealand cushion plant species

Cold adapted plants, such as cushion plants, may be particularly sensitive to climate warming because of their compact growth form and high branch density. In the oceanic southern hemisphere, cushion communities tend to have large range distributions at low latitudes (sea level to low alpine), thus providing an opportunity to test the effects of temperature on plant morphology and reproduction across gradients. Using Donatia novae‐zelandiae as a model species, we compared the leaf morphology, reproduction and responses to warming. Two low‐alpine sites (Maungatua (880 m a.s.l.), Blue Mountains (1000 m a.s.l.)) and two sea‐level sites (Waituna 1 (0 m a.s.l.), Waituna 2 (0 m a.s.l.)) in South Island, New Zealand were used. Donatia novae‐zelandiae cushions differed significantly between the high‐elevation and sea‐level sites both morphologically and in terms of reproduction. High‐elevation cushions produced more flowers (threefold more flowers per plant) and seeds (sevenfold more seeds per capsule) than at sea level, but leaves were larger at sea level (in length and specific leaf area). The cushions were also twice as compact at the high‐elevation sites. After two growing seasons of artificial warming, seed production (35%), leaf length (7%) and width (13%), and specific leaf area (63%) significantly decreased in D. novae‐zelandiae plants; flower production was not significantly affected. Cushion plant morphology and reproduction were significantly affected by environmental drivers at their establishment sites, but all populations responded negatively to artificial warming of 1–3°C. Many cushion plants are considered keystone species because of their propensity to facilitate the growth and establishment of other plant species, the inferred negative effects of global warming on cushion plant species may have a cascading effect on other alpine plant groups.     

A comparison of CFU-GM, BFU-E and endothelial progenitor cells using ex vivo expansion of selected cord blood CD133(+) and CD34(+) cells

BACKGROUND: CD133 is a newly developed hematopoietic stem cell marker but little is known about its function. Whether CD133(+) cell selection provides any advantage over CD34(+) selection for hematopoietic stem cell isolation and transplantation is unclear. The present study compared colony formation and endothelial cell differentiation of these two cell types from umbilical cord blood (UCB). METHODS: Mononuclear cells from the same UCB samples were used for both CD133(+) and CD34(+) cell selection. Cells with 97.1% purity were incubated in semi-solid culture medium containing stem cell growth factor (SCGF) and G-CSF or erythropoietin (EPO). Purified cells were also cultured in M199 containing vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and insulin-like growth factor-1 (IGF-1). RESULTS: CD34(+) and CD133(+) cells produced similar numbers of CFU-GM colonies (median 43.25 and 30.5, respectively; P>0.2). However, a greater than four-fold difference in BFU-E colony formation was observed from CD34(+) cells compared with CD133(+) cells (median 35 and 8, respectively; P<0.04). CD34(+) cells gave rise to endothelial-like cells when stimulated with VEGF, bFGF and IGF-1. CD133(+) cells were unable produce this cell type under the same conditions. DISCUSSION: CD133(+) cells produced smaller BFU-E colonies and were unable to differentiate into mature endothelial cells. CD34(+) cells contained endothelial progenitors that could differentiate into mature cells of this lineage. Based on these data, it appears that CD133 offers no distinct advantage over CD34 as a selective marker for immunoaffinity-based isolation of hematopoietic stem cells and endothelial progenitor cells.     

Decoding dumping ducks

Conspecific brood parasitism, where females of the same species lay eggs in each other's nests, is common in waterfowl, and is usually considered costly to host females, which are stuck looking after eggs and chicks that are not their own. However, since female waterfowl often exhibit an unusual propensity to nest near where they were born, there has been some uncertainty over whether, in ducks and geese, laying in nests of conspecifics really is parasitism. Do parasitic and host females tend to be related? And is parasitism actually a form of cooperation in disguise? In a population in Hudson Bay, Andersson & Waldeck (this issue) found that ‘parasitic’ eggs in nests of the common eider, Somateria mollissima sedentaria, are more closely related to host eggs than expected by chance. In fact, host and ‘donor’ eggs are more closely related than are females breeding at neighbouring nests. The Hudson Bay population of common eiders is unusual, because unlike in more benign climates, females do not tend to breed near their natal nest. Spatial proximity alone cannot account for the high relatedness between host eggs and ‘dumped’ or donor eggs. Instead, the high relatedness values are probably the result of active recognition, where females favour kin, either when dumping or accepting eggs. These new data, along with evidence indicating that the donor lays the first egg in the nest nearly half the time, suggest that what appears to be parasitism in common eiders may be a form of kin‐based cooperation.