Molecular mechanisms regulating formation,trafficking and processing of annular gap junctions

Internalization of gap junction plaques results in the formation of annular gap junction vesicles. The factors that regulate the coordinated internalization of the gap junction plaques to form annular gap junction vesicles, and the subsequent events involved in annular gap junction processing have only relatively recently been investigated in detail. However it is becoming clear that while annular gap junction vesicles have been demonstrated to be degraded by autophagosomal and endo-lysosomal pathways, they undergo a number of additional processing events. Here, we characterize the morphology of the annular gap junction vesicle and review the current knowledge of the processes involved in their formation, fission, fusion, and degradation. In addition, we address the possibility for connexin protein recycling back to the plasma membrane to contribute to gap junction formation and intercellular communication. Information on gap junction plaque removal from the plasma membrane and the subsequent processing of annular gap junction vesicles is critical to our understanding of cell-cell communication as it relates to events regulating development, cell homeostasis, unstable proliferation of cancer cells, wound healing, changes in the ischemic heart, and many other physiological and pathological cellular phenomena.

     

Dendro[C60]fullerene DF-1 provides radioprotection to radiosensitive mammalian cells

In this study, the ability of the C₆₀ fullerene derivative DF-1 to protect radiosensitive cells from the effects of high doses of gamma irradiation was examined. Earlier reports of DF-1’s lack of toxicity in these cells were confirmed, and DF-1 was also observed to protect both human lymphocytes and rat intestinal crypt cells against radiation-induced cell death. We determined that DF-1 protected both cell types against radiation-induced DNA damage, as measured by inhibition of micronucleus formation. DF-1 also reduced the levels of reactive oxygen species in the crypt cells, a unique capability of fullerenes because of their enhanced reactivity toward electron-rich species. The ability of DF-1 to protect against the cytotoxic effects of radiation was comparable to that of amifostine, another ROS-scavenging radioprotector. Interestingly, localization of fluorescently labeled DF-1 in fibroblast was observed throughout the cell. Taken together, these results suggest that DF-1 provides powerful protection against several deleterious cellular consequences of irradiation in mammalian systems including oxidative stress, DNA damage, and cell death.     

Coordination of photosynthetic traits across soil and climate gradients

“Least-cost theory” posits that C₃ plants should balance rates of photosynthetic water loss and carboxylation in relation to the relative acquisition and maintenance costs of resources required for these activities. Here we investigated the dependency of photosynthetic traits on climate and soil properties using a new Australia-wide trait dataset spanning 528 species from 67 sites. We tested the hypotheses that plants on relatively cold or dry sites, or on relatively more fertile sites, would typically operate at greater CO₂ drawdown (lower ratio of leaf internal to ambient CO₂, C_i:C_a) during light-saturated photosynthesis, and at higher leaf N per area (N_area) and higher carboxylation capacity (V_{cmax 25}) for a given rate of stomatal conductance to water vapour, g_sw. These results would be indicative of plants having relatively higher water costs than nutrient costs. In general, our hypotheses were supported. Soil total phosphorus (P) concentration and (more weakly) soil pH exerted positive effects on the N_area–g_sw and V_{cmax 25}–g_sw slopes, and negative effects on C_i:C_a. The P effect strengthened when the effect of climate was removed via partial regression. We observed similar trends with increasing soil cation exchange capacity and clay content, which affect soil nutrient availability, and found that soil properties explained similar amounts of variation in the focal traits as climate did. Although climate typically explained more trait variation than soil did, together they explained up to 52% of variation in the slope relationships and soil properties explained up to 30% of the variation in individual traits. Soils influenced photosynthetic traits as well as their coordination. In particular, the influence of soil P likely reflects the Australia's geologically ancient low-relief landscapes with highly leached soils. Least-cost theory provides a valuable framework for understanding trade-offs between resource costs and use in plants, including limiting soil nutrients.     

Individual bee foragers are less-efficient transporters of pollen for plants from which they collect the most pollen in their scopae

Premise

Bees provision most of the pollen removed from anthers to their larvae and transport only a small proportion to stigmas, which can negatively affect plant fitness. Though most bee species collect pollen from multiple plant species, we know little about how the efficiency of bees' pollen transport varies among host plant species or how it relates to other aspects of generalist bee foraging behavior that benefit plant fitness, such as specialization on individual foraging bouts.

Methods

We compared the pollen collected and transported by three bee species for 46 co-occurring plant species. Specifically, we compared the relative abundance of pollen taxa in the individual bees' scopae, structures where bees store pollen to provision larvae, with the relative abundance of pollen taxa on the rest of bees' bodies, which is more likely to be transferred to stigmas.

Results

Bees carried five times more pollen grains in their scopae than elsewhere on their bodies. Within foraging bouts, bees were relatively specialized in their pollen collection, but transported proportionally less pollen for the host plants on which they specialized. Across foraging bouts, two bee species transported proportionally less pollen for some of their host plants than for others, though differences didn't consistently follow the same trend as at the foraging bout scale.

Conclusions

Our results suggest that foraging-bout specialization, which is known to reduce heterospecific pollen transfer, also results in less-efficient pollen transport. Thus, bee foragers that visit predominantly one plant species may have contrasting effects on that plant's fitness.

     

Developmental profile of erythropoietin and its receptor in guinea-pig retina

Evidence suggests that endogenous erythropoietin (EPO) is involved in the development of the central nervous system; however, its role in retinal development is yet to be determined. In this study, we have used fluorescence immunohistochemistry to localise EPO and its receptor (EPOR) in the developing and mature retina of the guinea-pig, a species in which retinal development is similar to that in humans. EPO immunoreactivity (IR) was observed in ganglion cells from 25 days of gestation (dg; term ∼67 dg), and in the inner and outer plexiform layers and in horizontal cells by 40 dg. EPO-IR persisted in all of these structures into adulthood. Müller cells also displayed EPO-IR, which was seen in the radial processes and endfeet at 40 dg and in the cytoplasm by 50 dg. IR in these cells was particularly intense and appeared to increase with age. EPOR-IR was found in all ages examined; it was detected in ganglion cells at 25 dg and, from 30 dg onwards, was localised on, and adjacent to, the cell surface membrane. The distribution of EPOR-IR became increasingly widespread during gestation and, by 50 dg, EPOR-IR was detectable on the majority of retinal somal membranes. This localisation persisted in the postnatal and adult retina. Therefore, IR for EPO and its receptor is present in the guinea-pig retina from as early as 25 dg, when retinal layers are forming, and persists throughout postnatal development. This suggests that EPO plays a role both in retinal development and in the maintenance of the adult retina. This study was funded by the ANZ Charitable Trust; Medical Research and Technology in Victoria (M. Tolcos) and the National Health and Medical Research Council of Australia (M. Tolcos).     

Cultural transmission in the laboratory: agent interaction improves the intergenerational transfer of information

Cumulative cultural evolution requires that information is faithfully transmitted from generation to generation. The present study examines the role of agent interaction as a social learning mechanism through which information is transmitted across multiple generations. The performance of two types of linear transmission chains was compared: noninteractive (agents in adjacent chain positions were not permitted to interact) and interactive (adjacent agents freely interacted with one another). In both conditions, information (details of a narrative text) was lost as it was passed along the transmission chain. However, interactive transmission chains promoted more accurate recall of information than noninteractive chains. A content analysis revealed that most listeners actively participated in the information transfer process by seeking clarification and providing backchannel feedback to the narrator. Furthermore, the extent to which listeners engaged with the narrator was associated with narrator recall accuracy. Our results indicate that bidirectional agent interaction is an important consideration for studies of cultural transmission and cumulative cultural evolution.     

Na and k accumulation and salt tolerance of Atriplex canescens (Chenopodiaceae) genotypes

Sixteen accessions of the xerohalophyte, Atriplex canescens (Pursh.) Nutt., differing in tendency to accumulate Na or K in leaf tissues, were compared for salt tolerance in a greenhouse study. Plants were grown along a salinity gradient from 72 to 2017 mol/m³ NaCl measured in the root zone. Growth rates (RGR) were negatively affected by salinity for all accessions. Initial leaf levels of Na (measured before exposing plants to saline solutions) were positively correlated with subsequent RGR's of accessions on the salinity gradient (r = 0.60 - 0.88, P < 0.05 across salinity levels), whereas initial leaf K levels were negatively correlated (r = -0.68 to -0.85, P < 0.01 across salinity levels). Varieties linearis (S. Wats.) Munz and grandidentatum Stutz & Sanderson had greater tendency for Na accumulation, lower tendency for K, and higher growth rates on saline solutions than var. occidentalis (Torr. & Frem.) Welsh & Stutz accessions. Within var. occidentalis accessions, RGRs were negatively correlated with initial leaf levels of K but not Na. Postexposure leaf Na and K levels were not strongly correlated with RGR's. All accessions responded to salinity by increasing their uptake of Na, which is the primary mechanism of osmotic adjustment to salinity in this species. It is suggested that differences in tendency to accumulate Na or K among A. canescens genotypes are related to their specialization for saline or xeric habitats, respectively.