Oligomerization through hemopexin and cytoplasmic domains regulates the activity and turnover of membrane-type 1 matrix metalloproteinase.

The formation of multimeric complexes by membrane-type 1 matrix metalloproteinase (MT1-MMP) may facilitate its autocatalytic inactivation or proMMP-2 activation on the cell surface. To characterize these processes, we expressed various glutathione S-transferase/MT1-MMP fusion proteins in human HT-1080 fibrosarcoma cells and SV40-transformed lung fibroblasts and analyzed their effects on MT1-MMP activity and potential homophilic interactions. We report here that MT1-MMP is expressed on the cell surface as oligomeric 200--240-kDa complexes containing both the active 60-kDa and autocatalytically processed 43-kDa species. Overexpression of a glutathione S-transferase/MT1-MMP fusion protein containing the transmembrane and cytoplasmic domains of MT1-MMP inhibited the phorbol 12-myristate 13-acetate-induced autocatalytic cleavage of endogenous MT1-MMP to the 43-kDa species, but not proMMP-2 activation. On the other hand, a similar fusion protein with the hemopexin, transmembrane, and cytoplasmic domains inhibited proMMP-2 activation in a dominant-negative fashion. These results suggest that both the autocatalytic cleavage of MT1-MMP and proMMP-2 activation may be regulated by oligomerization through the cytoplasmic and hemopexin domains. Indeed, either domain, when attached to the cell membrane by a transmembrane domain, formed stable homophilic complexes. Copurification of MT1-MMP with these fusion proteins correlated with their cell-surface co-localization. Thus, MT1-MMP oligomerization through the hemopexin, transmembrane, and cytoplasmic domains controls its catalytic activity.     

Absence of seasonal variation in great tit offspring sex ratios

When the timing of breeding affects the reproductive value of sons and daughters differently, parents are expected to increase their fitness by changing the offspring sex ratio during the course of the breeding season. Previous studies have shown that in great tits Parus major hatching date has a stronger effect on the fitness of juvenile males than on that of juvenile females. We tested whether this difference was reflected in a seasonal decline in the proportion of sons per breeding attempt. Although offspring sex ratio was more variable than would be expected from a binomial distribution, there was no significant relationship between the proportion of sons and the laying date of the clutch. Moreover, individual females did not adjust the sex ratio of their offspring following an experimental delay of breeding. This study therefore fails to demonstrate adaptive seasonal variation in great tit offspring sex ratios.     

Strong seasonality may attenuate trophic cascades: vertebrate predator exclusion in boreal grassland

We studied the indirect effects of vertebrate predator exclusion on plant communities in boreal grassland in western Finland to find out whether the removal of the top trophic level would result in a trophic cascade. Predators were excluded from 1996 to 2000 by eight predator-proof fences (each 0.5 ha) constructed on old fields. Despite a major increase in vole densities, the expected trophic cascade attenuated rapidly so that the indirect effects of predator exclusion were restricted to a few plant species. The cause for the rapid attenuation of the trophic cascade appeared to be strong seasonality, as peak densities of voles were attained at the end of the growing season of vegetation, and vole populations declined before the next growing season so that the herbivory pressure during the growing season remained low or moderate. Accordingly, most plants escaped the heaviest grazing pressure either in time (plants completed their reproduction and withered before winter) or in space (living parts hidden under frozen ground and ice). However, heavy winter herbivory reduced the biomass of available vegetation and killed woody species (willows) at vole peaks, which implies that predator exclusion may have a strong effect on secondary succession. During summer, voles reduced the coverage of only a few preferred food plants ( Elymus repens , Phleum pratense , Vicia cracca ). Voles also maintained annual and biennial species in the community by creating gaps in the closed vegetation. We conclude that abiotic factors (harsh winter conditions) limited peak numbers of herbivores below a threshold density where herbivores could have caused a community-level decline in the biomass of herbaceous plants during summer.     

A comparison of the genetic and physical size of the streptomycin resistance locus in Pneumococcus.

Summary Polyacrylamide gel electrophoresis of the 30S ribosomal proteins derived from six streptomycin resistant strains indicates that each mutation alters the same ribosomal protein (str-r protein). Preliminary data utilizing SDS gels indicates that thestr-r protein has a molecular weight between 10,000 and 20,000 daltons. No significant differences could be detected between the molecular weight of thestr-r protein when it is derived either from a sensitive or from a resistant strain, including those derived from strains carrying multisite mutations of different genetic size. We have estimated the size of the multisitestr-r mutations to be less than 30 base pairs. Two factor crosses withstr-r markers in the trans position demonstrate recombination frequencies expected of closely linked, intragenic markers although cotransfer frequencies, of these same markers from the cis position, are very low. It is concluded that the cotransfer frequencies represent a marker effect and possible explanations are discussed. A reinterpretation of the genetic map of the pneumococcalstr-r locus is presented.Most of the material is taken from a thesis (ALR) submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Graduate Studies, of the State University of New York, Upstate Medical Center     

Proxy comparison in ancient peat sediments: pollen,macrofossil and plant DNA

We compared DNA, pollen and macrofossil data obtained from Weichselian interstadial (age more than 40 kyr) and Holocene (maximum age 8400 cal yr BP) peat sediments from northern Europe and used them to reconstruct contemporary floristic compositions at two sites. The majority of the samples provided plant DNA sequences of good quality with success amplification rates depending on age. DNA and sequencing analysis provided five plant taxa from the older site and nine taxa from the younger site, corresponding to 7% and 15% of the total number of taxa identified by the three proxies together. At both sites, pollen analysis detected the largest (54) and DNA the lowest (10) number of taxa, but five of the DNA taxa were not detected by pollen and macrofossils. The finding of a larger overlap between DNA and pollen than between DNA and macrofossils proxies seems to go against our previous suggestion based on lacustrine sediments that DNA originates principally from plant tissues and less from pollen. At both sites, we also detected Quercus spp. DNA, but few pollen grains were found in the record, and these are normally interpreted as long-distance dispersal. We confirm that in palaeoecological investigations, sedimentary DNA analysis is less comprehensive than classical morphological analysis, but is a complementary and important tool to obtain a more complete picture of past flora.     

Brood size manipulations within the natural range did not reveal intragenerational cost of reproduction in the Willow Tit Parus montanus

To test for the existence of a reproductive cost, we manipulated brood sizes (-2 and +2 nestlings) over 6 years in a northern population of Willow Tits Parus montanus breeding in natural holes. Possible effects were sought in subsequent survival and fecundity of the parents. Parents given extra chicks made more feeding visits than did parents with reduced and control broods. However, this was not reflected in differences in parental body-weight between groups at the end of the nestling period. Brood size manipulation did not significantly affect female or male survival. In 4 out of 6 years, there was a weak and nonsignificant effect on male survival, consistent with a cost of reproduction. Female and male fecundity in the year following the experiment was not affected by the manipulations. Thus, the data do not give evidence of an intragenerational cost of reproduction in the Willow Tit. Parents appeared unwilling to increase their breeding effort to a level which jeopardized their own survival or future breeding success. It is possible that, because of the time constraints in northern latitudes, females work under their capacity and lay smaller clutches than would otherwise be most profitable. Thus, no costs to the parents would be expected as a consequence of manipulations. These results suggest that the current reproductive rate is not maintained by reproductive cost in the Willow Tit. However, the results do not rule out the possibility that selection has operated outside the current range of reproductive rates during evolutionary history of the species.     

Temporal variability in detritus resource maintains diversity of bacterial communities

Competition theory generally predicts that diversity is maintained by temporal environmental fluctuations. One of the many suggested mechanisms for maintaining diversity in fluctuating environments is the gleaner-opportunist trade-off, whereby gleaner species have low threshold resource levels and low maximum growth rates in high resource concentration while opportunist species show opposite characteristics. We measured the growth rates of eight heterotrophic aquatic bacteria under different concentrations of chemically complex plant detritus resource. The growth rates revealed gleaner-opportunist trade-offs. The role of environmental variability in maintaining diversity was tested in a 28-day experiment with three different resource fluctuation regimes imposed on two four-species bacterial communities in microcosms. We recorded population densities with serial dilution plating and total biomass as turbidity. Changes in resource availability were measured from filter-sterilised medium by re-introducing the consumer species and recording short-term growth rates. The type of environmental variation had no effect on resource availability, which declined slowly during the experiment and differed in level between the communities. However, the slowly fluctuating environment had the highest Shannon diversity index, biomass, and coefficient of variation of biomass in both communities. We did not find a clear link between the gleaner-opportunist trade-off and diversity in fluctuating environments. Nevertheless, our results do not exclude this explanation and support the general view that temporal environmental variation maintains species diversity also in communities feeding chemically complex resource.     

SH3BP4 promotes neuropilin-1 and α5-integrin endocytosis and is inhibited by Akt

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Urea and Biuret as Nitrogen Sources for Rhizobium Spp.

Ability to utilize urea as nitrogen source proved to be universal in 80 fast and 40 slow growing strains of Rhizobium spp. from 23 genera of host plants, and also in 10 strains of Agrobacterium radiobacter. Rhizobium meliloti (32 strains) as well as A. radiobacter constantly failed to utilize biuret. Most rhizobia from other host plants (with 8 exceptions among 88) were able to use biuret as a somewhat suboptimal source of nitrogen, which was generally assimilated at a slower rate than urea and rarely resulted in the same amount of growth, particularly in the fast growing strains; in exceptional cases and mostly among the slow growing strains biuret appeared slightly superior to urea. Adaptation experiments showed that urease occurred as a constitutive enzyme in Rh. leguminosarum , while the biuret decomposing enzyme appeared to be inducible.