Abnormal growth plate function in pigs carrying a dominant mutation in type X collagen

We have identified a naturally occurring, dominant mutation that causes dwarfism in domestic pigs (Sus scrofa). With a positional candidate gene approach, the dwarf phenotype was shown to be a result of a single amino acid change, G590R, in the α1(X) chain of type X collagen. Type X collagen is a homotrimer of α1(X) chains encoded by the COL10A1 gene, which is expressed in hypertrophic chondrocytes during the process of endochondral ossification. An amino acid substitution at the equivalent position in human type X collagen, G595E, has previously been shown to cause Schmid metaphyseal chondrodysplasia (SMCD), which is a relatively mild skeletal disorder associated with dwarfism and growth plate abnormality. Consistent with the clinical phenotype of SMCD patients, radiological and histological examination of the dwarf pigs revealed metaphyseal chondrodysplasia in the long bones. Yeast-based, two-hybrid protein interaction studies and in vitro assembly experiments demonstrated that the amino acid substitution interfered with the ability of the mutated collagen molecules to engage in trimerization. This work establishes that the chondrodysplastic dwarf pigs by genetic, biochemical, radiological and histological criteria provide a valid animal model of SMCD. Received: 25 May 2000 / Accepted: 25 July 2000     

Higher resistance to herbivory in introduced compared to native populations of a seaweed

Non-indigenous species (NIS) are important components of global change, and in order to manage such species it is important to understand which factors affect their success. Interactions with enemies in the new range have been shown to be important for the outcome of introductions, but thus far most studies on NIS–enemy interactions have considered only specialist herbivores in terrestrial systems. Here we present the results from the first biogeographic study that compares herbivore resistance between populations in the native and new region of a non-indigenous seaweed. We show that low consumption of the non-indigenous seaweed by a generalist herbivore is caused by higher chemical defence levels and herbivore resistance in the new range—and not by the failure of the herbivore to recognise the non-indigenous seaweed as a suitable host. Since most seaweed–herbivore interactions are dominated by generalist herbivores, this pattern could be common in marine communities. Our results also reveal that traits used to predict the invasive potential of species, such as their resistance to enemies, can change during the invasion process, but not always in the way predicted by dominant theories.     

Migratory behaviour and otolith chemistry suggest fine-scale sub-population structure within a genetically homogenous Atlantic Cod population

The question whether temperate marine fishes typically consist of self-sustaining populations or “open” populations still remains unresolved. At the heart of this population connectivity problem lays the nature of the stock separation mechanisms. Fish populations could be segregated either by environmental forcing, accompanied with opportunistic recruitment of juveniles to spawning areas, or by philopatric behaviours (i.e., inclination of an individual to return to or remain in its natal area). Here we report three, partly independent, studies on Atlantic Cod (Gadus morhua) stock separation in the Kattegat and Öresund (eastern North Sea): characterisation of spawning aggregations with genetic markers, tagging experiments, and analysis of chemical constituents in otolith cores of recaptured fish that could be linked to a specific spawning site. While the genetic investigation showed no population segregation, the observed migratory patterns indicated three separate spawning sites at close distances. The natal dependence on the choice of spawning site was tested by measuring the contents of various trace elements in the otolith core of recaptured tagged fish. Quantification of the trace elements: Ba, Br, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sr, Ti, and Zn expressed as ratios to Ca were obtained using scanning micro PIXE. These results indicated that natal origin could be differentiated between spawning sites, supporting the hypothesis that natal homing is an important stock separating mechanism even over short distances (<100 km).     

Guanine Nucleotide-binding Protein (Gα) Endocytosis by a Cascade of Ubiquitin Binding Domain Proteins Is Required for Sustained Morphogenesis and Proper Mating in Yeast

Heterotrimeric G proteins are well known to transmit signals from cell surface receptors to intracellular effector proteins. There is growing appreciation that G proteins are also present at endomembrane compartments, where they can potentially interact with a distinct set of signaling proteins. Here, we examine the cellular trafficking function of the G protein α subunit in yeast, Gpa1. Gpa1 contains a unique 109-amino acid insert within the α-helical domain that undergoes a variety of posttranslational modifications. Among these is monoubiquitination, catalyzed by the NEDD4 family ubiquitin ligase Rsp5. Using a newly optimized method for G protein purification together with biophysical measures of structure and function, we show that the ubiquitination domain does not influence enzyme activity. By screening a panel of 39 gene deletion mutants, each lacking a different ubiquitin binding domain protein, we identify seven that are necessary to deliver Gpa1 to the vacuole compartment including four proteins (Ede1, Bul1, Ddi1, and Rup1) previously not known to be involved in this process. Finally, we show that proper endocytosis of the G protein is needed for sustained cellular morphogenesis and mating in response to pheromone stimulation. We conclude that a cascade of ubiquitin-binding proteins serves to deliver the G protein to its final destination within the cell. In this instance and in contrast to the previously characterized visual system, endocytosis from the plasma membrane is needed for proper signal transduction rather than for signal desensitization.     

Subtypes of non-transformed human mammary epithelial cells cultured in vitro: histo-blood group antigen H type 2 defines basal cell-derived cells

Abstract. Normal (non-transformed) human mammary epithelial cell lines derived from reduction mammoplasties were analyzed by immunocytochemistry with more than 80 monoclonal antibodies (mAbs) and other specific reagents to tissue-specific and developmentally regulated antigens at different passage levels. A subpopulation of poorly differentiated, proliferating epithelial cells, corresponding to the 'selected' cell type of late passages, is shown to be characterized by a new marker, the histo-blood group antigen H type 2, probably carried on a membrane-bound glycolipid. These cells also express a number of other onco-developmental carbohydrate antigens [Le^y, Le^x, sialosyl-Le^a, precursor of Thomsen Friedenreich antigen (T_n), but not Thomsen-Friedenreich antigen and sialosyl-T_n). Their cytokeratin (CK) phenotype, as assessed by reactivity with monospecific mAbs and two-dimensional gel electrophoresis, is CK 5, 6, 14 and 17, with CK 19 being consistently absent, and varying minor amounts of CK 7, 8 and 18, as well as 15 and 16. The reactivity of these cells with a panel of 11 mAbs specific for CK 18 varies considerably even after cloning, indicating heterogeneity of epitope expression or accessibility. Our data strongly suggest that the H type 2⁺ cells develop from the basal cell layer of the mammary gland.     

Commonness of Amazonian palm (Arecaceae) species: Cross-scale links and potential determinants

The mechanisms that cause variation in commonness (abundances and range sizes) of species remain debated in ecology, and a repeatedly observed pattern is the positive relation between local abundances and larger scale range sizes. We used the Amazonian palm species (Arecaceae) to investigate the dependence between and potential determinants of commonness across three (local, landscape, continental) spatial scales. Commonness at the smaller scales (local abundance, landscape frequency) was estimated using data from 57 transects (5 × 500 m) in primary, non-inundated (terra firme) rainforest in a western Amazonian landscape, while commonness at the largest scale (continental range size) was estimated from digitized distribution maps. Landscape frequency was positively related to both local abundance and continental range size, which, however, were not related to each other. Landscape frequency was positively related to topographic niche breadth. Stem height correlated with continental range size and was the only species life-history trait related to any commonness measure. Distance from the study area to a species' range centre did not influence any of the commonness measures. The factors determining commonness in the Amazonian palm flora appear to be scale-dependent, with the unrelated local scale abundance and continental range size probably being controlled by different driving factors. Interestingly, commonness at the intermediate, landscape scale seems linked to both the smaller and the larger scale. Our results point towards topographic niche breadth at the smaller scales and stem height, possibly reflecting species' dispersal potential, at the continental scale as important determinants of commonness.