Mutation of Membrane Type-1 Metalloproteinase, MT1-MMP, Causes the Multicentric Osteolysis and Arthritis Disease Winchester Syndrome

The "vanishing bone" syndromes represent a group of rare skeletal disorders characterized by osteolysis and joint destruction, which can mimic severe rheumatoid arthritis. Winchester syndrome was one of the first recognized autosomal-recessive, multicentric forms of the disorder. It was originally described nearly 50 years ago in two sisters with a severe crippling osteolysis. Using cultured fibroblasts from the proband, we have now identified homozygous mutations in membrane type-1 metalloproteinase (MT1-MMP or MMP14). We demonstrate that the resulting hydrophobic-region signal-peptide substitution (p.Thr17Arg) decreases MT1-MMP membrane localization with consequent impairment of pro-MMP2 activation, and we propose a structure-based mechanism for this effect.     

Hsp70 promotes epithelial sodium channel functional expression by increasing its association with coat complex II and its exit from endoplasmic reticulum

The epithelial sodium channel (ENaC) plays an important role in the homeostasis of blood pressure and of the airway surface liquid, and inappropriate regulation of ENaC results in refractory hypertension (in Liddle syndrome) and impaired mucociliary clearance (in cystic fibrosis). The regulation of ENaC by molecular chaperones, such as the 70-kDa heat shock protein Hsp70, is not completely understood. Building on the previous suggestion by our group that Hsp70 promotes ENaC functional and surface expression in Xenopus oocytes, we investigated the mechanism by which Hsp70 acts upon ENaC in epithelial cells. In Madin-Darby canine kidney cells stably expressing epitope-tagged αβγ-ENaC and with tetracycline-inducible overexpression of Hsp70, treatment with 1 or 2 μg/ml doxycycline increased total Hsp70 expression ~2-fold and ENaC functional expression ~1.4-fold. This increase in ENaC functional expression corresponded to an increase in ENaC expression at the apical surface of the cells and was not present when an ATPase-deficient Hsp70 was similarly overexpressed. The increase in functional expression was not due to a change in the rate at which ENaC was retrieved from the apical membrane. Instead, Hsp70 overexpression increased the association of ENaC with the Sec24D cargo recognition component of coat complex II, which carries protein cargo from the endoplasmic reticulum to the Golgi. These data support the hypothesis that Hsp70 promotes ENaC biogenesis and trafficking to the apical surface of epithelial cells.     

How avian incubation behaviour influences egg surface temperatures: relationships with egg position,development and clutch size

While understanding heat exchange between incubating adults and their eggs is central to the study of avian incubation energetics, current theory based on thermal measurements from dummy eggs reveals little about the mechanisms of this heat exchange or behavioural implications for the incubating bird. For example, we know little about how birds distribute their eggs based on temperature differences among egg positions within the nest cup. We studied the great tit Parus major, a species with a large clutch size, to investigate surface cooling rates of individual eggs within the nest cup across a range of ambient temperatures in a field situation. Using state‐of‐the‐art portable infrared imaging and digital photography we tested for associations between egg surface temperature (and rate of cooling) and a combination of egg specific (mass, shape, laying order, position within clutch) and incubation specific (clutch size, ambient temperature, day of incubation) variables. Egg surface temperature and cooling rates were related to the position of the eggs within the nest cup, with outer eggs being initially colder and cooling quicker than central eggs. Between foraging bouts, females moved outer eggs significantly more than centrally positioned eggs. Our results demonstrate that females are capable of responding to individual egg temperature by moving eggs around the nest cup, and that the energy cost to the female may increase as incubation proceeds. In addition, our results showing that smaller clutches experience lower initial incubation temperatures and cool quicker than larger clutches warrant further attention for optimal clutch size theory and studies of energetic constraints during incubation. Finally, researchers using dummy eggs to record egg temperature have ignored important elements of contact‐incubation, namely the complexity of how eggs cool and how females respond to these changes.     

A biomechanical role for perlecan in the pericellular matrix of articular cartilage

Chondrocytes are surrounded by a narrow pericellular matrix (PCM) that is biochemically, structurally, and biomechanically distinct from the bulk extracellular matrix (ECM) of articular cartilage. While the PCM is often defined by the presence of type VI collagen, other macromolecules such as perlecan, a heparan sulfate (HS) proteoglycan, are also exclusively localized to the PCM in normal cartilage and likely contribute to PCM structural integrity and biomechanical properties. Though perlecan is essential for normal cartilage development, its exact role in the PCM is unknown. The objective of this study was to determine the biomechanical role of perlecan in the articular cartilage PCM in situ and its potential as a defining factor of the PCM. To this end, atomic force microscopy (AFM) stiffness mapping was combined with dual immunofluorescence labeling of cryosectioned porcine cartilage samples for type VI collagen and perlecan. While there was no difference in overall PCM mechanical properties between type VI collagen- and perlecan-based definitions of the PCM, within the PCM, interior regions containing both type VI collagen and perlecan exhibited lower elastic moduli than more peripheral regions rich in type VI collagen alone. Enzymatic removal of HS chains from perlecan with heparinase III increased PCM elastic moduli both overall and locally in interior regions rich in both perlecan and type VI collagen. Heparinase III digestion had no effect on ECM elastic moduli. Our findings provide new evidence for perlecan as a defining factor in both the biochemical and biomechanical properties of the PCM.     

Late-successional biological soil crusts in a biodiversity hotspot: an example of congruency in species richness

Understanding the biodiversity of functionally important communities in Earth’s ecosystems is vital in the apportionment of limited ecosystem management funds and efforts. In southern California shrublands, which lie in a global biodiversity hotspot, biological soil crusts (BSCs) confer critical ecosystem services; however, their biodiversity remains unknown. In this study, six sites (n = 4 each, 25 m²) were established along a mediterranean shrubland environmental gradient in southern California. Here, the biodiversity of all BSC-forming lichens and bryophytes was evaluated, related to environmental traits along the gradient, and compared to species richness among North American ecosystems supporting BSCs (data from previous studies). In total, 59 BSC-forming lichens and bryophytes were observed, including the very rare Sarcogyne crustacea, a rare moss, and five endemic lichen species. Over half (61%) of the species observed were found at a single site. Along the gradient, species evenness of late-successional BSC was related to dew point and elevation, and both evenness and richness were related to distance to coast. Using an ordination analysis, five distinct late-successional BSC communities were identified: Riversidian, Spike moss, Casperian, Alisian, and Lagunian. Twenty-five lichens and 19 bryophytes are newly reported for North American BSC-forming organisms, now comprising ~1/2 of the North American total. BSCs in North American hot and cold deserts were approximately 4.0 and 2.4 times less species rich than BSCs found in southern California shrublands, respectively. Given the anthropogenic impacts on quality and distribution of California mediterranean shrublands, our results show that these sites represent important refugia of BSC species in this globally important region.     

Protein storage and root:shoot reallocation provide tolerance to damage in a hybrid willow system

To determine the mechanistic basis of tolerance, we evaluated six candidate traits for tolerance to damage using F₂ interspecific hybrids in a willow hybrid system. A distinction was made between reproductive tolerance and biomass tolerance; reproductive tolerance was designated as a plant’s proportional change in catkin production following damage, while biomass tolerance referred to a plant’s proportional change in biomass (i.e., regrowth) following damage. F₂ hybrids were generated to increase variation and independence among candidate traits. Using three clonally identical individuals, pre-damage candidate traits for tolerance to damage (root:shoot ratio, total nonstructural carbohydrate, and total available protein) and post-damage candidate traits (relative root:shoot ratio, phenolic ratio, and specific leaf area ratio) were measured. The range of variation for these six candidate traits was broad. Biomass was significantly increased two years after 50% shoot length removal, and catkin production was not significantly reduced when damaged, suggesting that F₂ hybrids had great biomass tolerance and reproductive tolerance. Based on multiple regression methods, increased reproductive tolerance was associated with increased protein storage and decreased relative root:shoot ratio (reduced root allocation after damage). In addition, a positive relationship between biomass tolerance and condensed tannins was detected, and both traits were associated with increased reproductive tolerance. These four factors explained 57% of the variance in the reproductive tolerance of F₂ hybrids, but biomass tolerance explained the majority of the variance in reproductive tolerance. Changes in plant architecture in response to plant damage may be the underlying mechanism that explains biomass tolerance.     

The use of specialisation indices to predict vulnerability of coral‐feeding butterflyfishes to environmental change

In the absence of detailed assessments of extinction risk, ecological specialisation is often used as a proxy of vulnerability to environmental disturbances and extinction risk. Numerous indices can be used to estimate specialisation; however, the utility of these different indices to predict vulnerability to future environmental change is unknown. Here we compare the performance of specialisation indices using coral‐feeding butterflyfishes as a model group. Our aims were to 1) quantify the dietary preferences of three butterflyfish species across habitats with differing levels of resource availability; 2) investigate how estimates of dietary specialisation vary with the use of different specialisation indices; 3) determine which specialisation indices best inform predictions of vulnerability to environmental change; and 4) assess the utility of resource selection functions to inform predictions of vulnerability to environmental change. The relative level of dietary specialisation estimated for all three species varied when different specialisation indices were used, indicating that the choice of index can have a considerable impact upon estimates of specialisation. Specialisation indices that do not consider resource abundance may fail to distinguish species that primarily use common resources from species that actively target resources disproportionately more than they are available. Resource selection functions provided the greatest insights into the potential response of species to changes in resource availability. Examination of resource selection functions, in addition to specialisation indices, indicated that Chaetodon trifascialis was the most specialised feeder, with highly conserved dietary preferences across all sites, suggesting that this species is highly vulnerable to the impacts of climate‐induced coral loss on reefs. Our results indicate that vulnerability assessments based on some specialisation indices may be misleading and the best estimates of dietary specialisation will be provided by indices which incorporate resource availability measures, as well as assessing responses of species to changes in resource availability.