Primary structure and developmental expression of Dp ZP2, a vitelline envelope glycoprotein homolog of mouse ZP2, in Discoglossus pictus, one of the oldest living Anuran species

A glycoprotein of the Xenopus vitelline envelope, gp 69/64, which mediates sperm binding, is closely related to the components of ZPA family, such as the mouse zona pellucida ZP2. To test the generality of these findings, we studied Discoglossus pictus, a species evolutionary distant from Xenopus and identified as a protein of 63 kDa in the vitelline envelope. Preliminary studies suggest that this protein may bind sperm at fertilization. We found that the 63-kDa protein is glycosylated and contains both N- and O-linked chains. We have cloned the cDNA encoding the Discoglossus protein of 63 kDa (Dp ZP2) by screening a Discoglossus cDNA library using Xenopus gp 69/64 cDNA as a probe. Analysis of the deduced sequence of Discoglossus protein revealed 48% identity with Xenopus gp 69/64 and 37-40% identity with mouse ZP2. The sequence conservation included a ZP domain, a potential furin cleavage site and a putative transmembrane domain. The N-terminus region of Dp ZP2 was 40% identical to the corresponding region of Xenopus gp 69/64 which has been shown to be essential for sperm binding to the VE. Although, as of yet, there is no evidence for sperm binding at the Dp ZP2 N-terminus, it is interesting that in this region three potential O-glycosylation sites are conserved in both species, in contrast to N-glycosylation sites. It was found that the Dp ZP2 mRNA is expressed in stage 1 oocytes and in the follicle cells surrounding the oocyte. Similarly, in Xenopus oocytes, the gp 69/64m RNA, was found in the oocytes, as well as in the somatic cells. Mol. Reprod. Dev. 59:133-143, 2001.     

Finding statistically significant communities in networks

Community structure is one of the main structural features of networks, revealing both their internal organization and the similarity of their elementary units. Despite the large variety of methods proposed to detect communities in graphs, there is a big need for multi-purpose techniques, able to handle different types of datasets and the subtleties of community structure. In this paper we present OSLOM (Order Statistics Local Optimization Method), the first method capable to detect clusters in networks accounting for edge directions, edge weights, overlapping communities, hierarchies and community dynamics. It is based on the local optimization of a fitness function expressing the statistical significance of clusters with respect to random fluctuations, which is estimated with tools of Extreme and Order Statistics. OSLOM can be used alone or as a refinement procedure of partitions/covers delivered by other techniques. We have also implemented sequential algorithms combining OSLOM with other fast techniques, so that the community structure of very large networks can be uncovered. Our method has a comparable performance as the best existing algorithms on artificial benchmark graphs. Several applications on real networks are shown as well. OSLOM is implemented in a freely available software (http://www.oslom.org), and we believe it will be a valuable tool in the analysis of networks.     

Developmental pathways that generate natural-killer-cell diversity in mice and humans

Natural killer (NK) cells are large granular lymphocytes capable of producing inflammatory cytokines and spontaneously killing malignant, infected or 'stressed' cells. These NK-cell functions are controlled by cell-surface receptors that titrate stimulatory and inhibitory signals. However, we remain puzzled about where and when NK cells develop and differentiate, and this has fuelled the debate over the diversification of the peripheral NK-cell pool: are NK cells functionally homogeneous or are there subsets with specialized effector functions? In this Review, we consider the developmental relationships and biological significance of the diverse NK-cell subsets in mice and humans, and discuss how new humanized mouse models may help to characterize them further.     

Effects of water stress on gas exchange of field grown <Emphasis Type="Italic">Zea mays</Emphasis> L. in Southern Italy: an analysis at canopy and leaf level

Zea mays is cultivated in the Mediterranean regions where summer drought may lead to photoinhibition when irrigation is not available. In this work the response of maize to water stress was evaluated by gas exchange measurements at the canopy and leaf level. Leaf gas exchange was assessed before, during and after water stress, while canopy turbulent fluxes of mass and energy were performed on a continuous basis. In the early growth period, a linear increment of net ecosystem photosynthetic rate (P _NE) to incoming of photosynthetic photon flux density (PPFD) was found and net leaf photosynthetic rate (P _NL) showed the tendency to saturate under high irradiance. During water stress, the relationship between P _NE and PPFD became curvilinear and both P _NE and P _NL saturated in a range between 1,000 and 1,500 μmol (photons) m⁻² s⁻¹. Leaf water potential (ψ_l) dropped from −1.50 to −1.88 MPa during water stress, indicating that leaf and canopy gas exchanges were limited by stomatal conductance. With the restoration of irrigation, P _NE, P _NL and ψ_l showed a recovery, and P _NE and P _NL reached the highest values of whole study period. Leaf area index (LAI) reached a value of 3.0 m² m⁻². The relationship between P _NE and PPFD remained curvilinear and P _NE values were lower than those of a typical well-irrigated maize crop. The recovery in P _NE and P _NL after stress, and ψ_l values during stress indicate that the photosynthetic apparatus was not damaged while soil moisture stress after-effects resulted in a sub-optimal LAI values, which in turn depressed P _NE.     

Growth and gas exchange response to water shortage of a maize crop on different soil types

The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early leaf senescence. Canopy and leaf gas exchanges, measured by eddy correlation technique and by a portable photosynthetic system, respectively, were affected by water stress and a greater reduction in net photosynthetic rate (A _N) and stomatal conductance (g _s) was observed on SS. Chlorophyll and carotenoids content was not affected by water shortage in either condition. Results support two main conclusions: (1) leaf photosynthetic capacity was unaffected by water stress, and (2) maize effectively endured water shortage during the vegetative growth stage.