Martha Betson

Actin at cell-cell junctions is composed of two dynamic and functional populations

The ability of epithelial cells to polarize requires cell-cell adhesion mediated by cadherin receptors. During cell-cell contact, the mechanism via which a flat, spread cell shape is changed into a tall, cuboidal epithelial morphology is not known. We found that cadherin-dependent adhesion modulates actin dynamics by triggering changes in actin organization both locally at junctions and within the rest of the cell. Upon induction of cell-cell contacts, two spatial actin populations are distinguishable: junctional actin and peripheral thin bundles. With time, the relative position of these two populations changes and becomes indistinguishable to form a cortical actin ring that is characteristic of mature, fully polarized epithelial cells. Junctional actin and thin actin bundles differ in their actin dynamics and mechanism of formation, and interestingly, have distinct roles during epithelial polarization. Whereas junctional actin stabilizes clustered cadherin receptors at cell-cell contacts, contraction of peripheral actin bundle is essential for an increase in the maximum height at the lateral domain during polarization (cuboidal morphology). Thus, both junctional actin and thin bundles are necessary, and cooperate with each other to generate a polarized epithelial morphology.

Rac Activation upon Cell-Cell Contact Formation Is Dependent on Signaling from the Epidermal Growth Factor Receptor

Cadherins are transmembrane receptors that mediate cell-cell adhesion. They play an essential role in embryonic development and maintenance of tissue architecture. The Rho family small GTPases regulate actin cytoskeletal dynamics in different cell types. The function of two family members, Rho and Rac, is required for the stability of cadherins at cell-cell contacts. Consistent with the published data we have found that Rac is activated upon induction of intercellular adhesion in epithelial cells. This activation is dependent on functional cadherins (Nakagawa, M., Fukata, M., Yamaga, M., Itoh, N., and Kaibuchi, K. (2001) J. Cell Sci. 114, 1829–1838; Noren, N. K., Niessen, C. M., Gumbiner, B. M., and Burridge, K. (2001) J. Biol. Chem. 276, 3305–3308). Here we show for the first time that clustering of cadherins using antibody-coated beads is sufficient to promote Rac activation. In the presence of Latrunculin B, Rac can be partially activated by antibody-clustered cadherins. These results suggest that actin polymerization is not required for initial Rac activation. Contrary to what has been described before, phosphatidylinositol 3-kinases are not involved in Rac activation following cell-cell adhesion in keratinocytes. Interestingly, inhibition of epidermal growth factor receptor signaling efficiently blocks the increased Rac-GTP levels observed after contact formation. We conclude that cadherin-dependent adhesion can activate Rac via epidermal growth factor receptor signaling.

Schistosomiasis in African infants and preschool children: let them now be treated!

The occurrence of schistosomiasis within African infants and preschool children has been much better documented in recent years, revealing an important burden of disease previously overlooked. Despite mounting evidence showing that treatment with praziquantel is safe, beneficial, and could be delivered within ongoing public health interventions, young children still do not have satisfactory access to this drug, and a significant treatment gap exists. Progress towards resolution of this unfortunate health inequity is highlighted, including the development of an appropriate paediatric praziquantel formulation, and present blocks are identified on securing this issue within the international health agenda.

The Drosophila ATM Ortholog, dATM, Mediates the Response to Ionizing Radiation and to Spontaneous DNA Damage during Development

Cells of metazoan organisms respond to DNA damage by arresting their cell cycle to repair DNA, or they undergo apoptosis. Two protein kinases, ataxia-telangiectasia mutated (ATM) and ATM and Rad-3 related (ATR), are sensors for DNA damage. In humans, ATM is mutated in patients with ataxia-telangiectasia (A-T), resulting in hypersensitivity to ionizing radiation (IR) and increased cancer susceptibility. Cells from A-T patients exhibit chromosome aberrations and excessive spontaneous apoptosis. We used Drosophila as a model system to study ATM function. Previous studies suggest that mei-41 corresponds to ATM in Drosophila; however, it appears that mei-41 is probably the ATR ortholog. Unlike mei-41 mutants, flies deficient for the true ATM ortholog, dATM, die as pupae or eclose with eye and wing abnormalities. Developing larval discs exhibit substantially increased spontaneous chromosomal telomere fusions and p53-dependent apoptosis. These developmental phenotypes are unique to dATM, and both dATM and mei-41 have temporally distinct roles in G2 arrest after IR. Thus, ATM and ATR orthologs are required for different functions in Drosophila; the developmental defects resulting from absence of dATM suggest an important role in mediating a protective checkpoint against DNA damage arising during normal cell proliferation and differentiation.

Treatment of intestinal schistosomiasis in Ugandan preschool children: best diagnosis, treatment efficacy and side-effects, and an extended praziquantel dosing pole

Summary The Ugandan national control programme for schistosomiasis has no clear policy for inclusion of preschool-children (≤5 years old) children. To re-balance this health inequality, we sought to identify best diagnosis of intestinal schistosomiasis, observe treatment safety and efficacy of praziquantel (PZQ), and extend the current WHO dose pole for chemotherapy. We examined and treated 363 preschool children from shoreline villages of Lakes Albert and Victoria, and found that 62·3% (CI95 57·1–67·3) of the children were confirmed to have intestinal schistosomiasis. One day after treatment, children were reported as having headaches (3·6%), vomiting (9·4%), diarrhoea (10·9%) and urticaria/rash (8·9%) with amelioration at 21-day follow-up, where the parasitological cure rate was found to be 100·0%. Height and weight data were collected from a further 3303 preschool children to establish and validate an extended PZQ dose pole that now includes two new height-intervals: 60–84 cm for one-half tablet and 84–99 cm for three-quarter tablet divisions; which would result in 97·6% of children receiving an acceptable dose (30–60 mg/kg). To conclude, preschool children in lakeshore communities of Uganda are at significant risk of intestinal schistosomiasis; we now strongly advocate for their immediate inclusion within the national control programme to eliminate this health inequity.

Plasmodium ovale curtisi and Plasmodium ovale wallikeri circulate simultaneously in African communities

Graphical abstract Research highlights ► We propose that two related species of malaria parasite cause ovale malaria. ► Discriminatory PCR tests identified both species in African surveys. ► Plasmodium ovale curtisi and Plasmodium ovale wallikeri were found together in time and space. ► Lack of recombination between them is not due to geographic or temporal separation. ► Therefore, the species barrier may be maintained by a biological mechanism(s).

Schistosoma mansoni Infections in Young Children: When Are Schistosome Antigens in Urine, Eggs in Stool and Antibodies to Eggs First Detectable?

Background In Uganda, control of intestinal schistosomiasis with preventive chemotherapy is typically focused towards treatment of school-aged children; the needs of younger children are presently being investigated as in lakeshore communities very young children can be infected. In the context of future epidemiological monitoring, we sought to compare the detection thresholds of available diagnostic tools for Schistosoma mansoni and estimate a likely age of first infection for these children. Methods and Findings A total of 242 infants and preschool children (134 boys and 108 girls, mean age 2.9 years, minimum 5 months and maximum 5 years) were examined from Bugoigo, a well-known disease endemic village on Lake Albert. Schistosome antigens in urine, eggs in stool and host antibodies to eggs were inspected to reveal a general prevalence of 47.5% (CI95 41.1–54.0%), as ascertained by a positive criterion from at least one diagnostic method. Although children as young as 6 months old could be found infected, the average age of infected children was between 3¼–3¾ years, when diagnostic techniques became broadly congruent. Conclusion Whilst different assays have particular (dis)advantages, direct detection of eggs in stool was least sensitive having a temporal lag behind antigen and antibody methods. Setting precisely a general age of first infection is problematic but if present Ugandan policies continue, a large proportion of infected children could wait up to 3–4 years before receiving first medication. To better tailor treatment needs for this younger ageclass, we suggest that the circulating cathodic antigen urine dipstick method to be used as an epidemiological indicator.

Closing the praziquantel treatment gap: new steps in epidemiological monitoring and control of schistosomiasis in African infants and preschool-aged children

SUMMARY Where very young children come into contact with water containing schistosome cercariae, infections occur and schistosomiasis can be found. In high transmission environments, where mothers daily bathe their children with environmentally drawn water, many infants and preschool-aged children have schistosomiasis. This ‘new’ burden, inclusive of co-infections with Schistosoma haematobium and Schistosoma mansoni, is being formally explored as infected children are not presently targeted to receive praziquantel (PZQ) within current preventive chemotherapy campaigns. Thus an important PZQ treatment gap exists whereby infected children might wait up to 4–5 years before receiving first treatment in school. International treatment guidelines, set within national treatment platforms, are presently being modified to provide earlier access to medication(s). Although detailed pharmacokinetic studies are needed, to facilitate pragmatic dosing in the field, an extended ‘dose pole’ has been devised and epidemiological monitoring has shown that administration of PZQ (40 mg/kg), in either crushed tablet or liquid suspension, is both safe and effective in this younger age-class; drug efficacy, however, against S. mansoni appears to diminish after repeated rounds of treatment. Thus use of PZQ should be combined with appropriate health education/water hygiene improvements for both child and mother to bring forth a more enduring solution.

Armus is a Rac1 effector that inactivates Rab7 and regulates E-cadherin degradation.

BACKGROUND Cell-cell adhesion and intracellular trafficking are regulated by signaling pathways from small GTPases of the Rho, Arf, and Rab subfamilies. How signaling from distinct small GTPases are integrated in a given process is poorly understood. RESULTS We find that a TBC/RabGAP protein, Armus, integrates signaling between Arf6, Rac1, and Rab7 during junction disassembly. Armus binds specifically to activated Rac1 and its C-terminal TBC/RabGAP domain inactivates Rab7. Thus, Armus is a novel Rac1 effector and a bona fide GAP for Rab7 in vitro and in vivo, a unique and previously unreported combination. Arf6 activation efficiently disrupts cell-cell contacts and is known to activate Rac1 and Rab7. Arf6-induced E-cadherin degradation is efficiently blocked by expression of Armus C-terminal domain or after Armus RNAi. Coexpression of Arf6 with dominant-negative Rab7 or Rac1 also inhibits junction disassembly. Importantly, Armus RabGAP expression also prevents EGF-induced scattering in keratinocytes, a process shown here to require Arf6, Rac1, and Rab7 function. To our knowledge, this is the first report to demonstrate a molecular and functional link between Rac1 and Rab7. CONCLUSIONS Our data indicate that active Rac1 recruits Armus to locally inactivate Rab7 and facilitate E-cadherin degradation in lysosomes. Thus, the integration of Rac1 and Rab7 activities by Armus provides an important regulatory node for E-cadherin turnover and stability of cell-cell contacts.

Molecular Epidemiology of Ascariasis: A Global Perspective on the Transmission Dynamics of Ascaris in People and Pigs

Background. The roundworm Ascaris lumbricoides infects 0.8 billion people worldwide, and Ascaris suum infects innumerable pigs across the globe. The extent of natural cross-transmission of Ascaris between pig and human hosts in different geographical settings is unknown, warranting investigation. Methods. Adult Ascaris organisms were obtained from humans and pigs in Europe, Africa, Asia, and Latin America. Barcodes were assigned to 536 parasites on the basis of sequence analysis of the mitochondrial cytochrome c oxidase I gene. Genotyping of 410 worms was also conducted using a panel of microsatellite markers. Phylogenetic, population genetic, and Bayesian assignment methods were used for analysis. Results. There was marked genetic segregation between worms originating from human hosts and those originating from pig hosts. However, human Ascaris infections in Europe were of pig origin, and there was evidence of cross-transmission between humans and pigs in Africa. Significant genetic differentiation exists between parasite populations from different countries, villages, and hosts. Conclusions. In conducting an analysis of variation within Ascaris populations from pig and human hosts across the globe, we demonstrate that cross-transmission takes place in developing and developed countries, contingent upon epidemiological potential and local phylogeography. Our results provide novel insights into the transmission dynamics and speciation of Ascaris worms from humans and pigs that are of importance for control programs.