Protecting the peri-domestic environment: the challenge for eliminating residual malaria.

Malaria transmission after universal access and use of malaria preventive services is known as residual malaria transmission. The concurrent spatial-temporal distributions of people and biting mosquitoes in malaria endemic villages determines where and when residual malaria transmission occurs. Understanding human and vector population behaviors and movements is a critical first step to prevent mosquito bites to eliminate residual malaria transmission. This study identified where people in the Solomon Islands are over 24-hour periods. Participants (59%) were predominantly around the house but not in their house when most biting by Anopheles farauti, the dominant malaria vector, occurs. While 84% of people slept under a long-lasting insecticide-treated bed net (LLIN), on average only 7% were under an LLIN during the 18:00 to 21:00 h peak mosquito biting period. On average, 34% of participants spend at least one night away from their homes each fortnight. Despite high LLIN use while sleeping, most human biting by An. farauti occurs early in the evening before people go to sleep when people are in peri-domestic areas (predominantly on verandas or in kitchen areas). Novel vector control tools that protect individuals from mosquito bites between sundown and when people sleep are needed for peri-domestic areas.

Unique fine scale village spatial-temporal distributions of Anopheles farauti differ by physiological state and sex.

BACKGROUND: The ecology of many mosquitoes, including Anopheles farauti, the dominant malaria vector in the southwest Pacific including the Solomon Islands, remains inadequately understood. Studies to map fine scale vector distributions are biased when trapping techniques use lures that will influence the natural movements of mosquitoes by attracting them to traps. However, passive collection methods allow the detailed natural distributions of vector populations by sex and physiological states to be revealed. METHODS: The barrier screen, a passive mosquito collection method along with human landing catches were used to record An. farauti distributions over time and space in two Solomon Island villages from May 2016 to July 2017. RESULTS: Temporal and spatial distributions of over 15,000 mosquitoes, including males as well as unfed, host seeking, blood-fed, non-blood fed and gravid females were mapped. These spatial and temporal patterns varied by species, sex and physiological state. Sugar-fed An. farauti were mostly collected between 10-20 m away from houses with peak activity from 18:00 to 19:00 h. Male An. farauti were mostly collected greater than 20 m from houses with peak activity from 19:00 to 20:00 h. CONCLUSIONS: Anopheles farauti subpopulations, as defined by physiological state and sex, are heterogeneously distributed in Solomon Island villages. Understanding the basis for these observed heterogeneities will lead to more accurate surveillance of mosquitoes and will enable spatial targeting of interventions for greater efficiency and effectiveness of vector control.

Human exposure to Anopheles farauti bites in the Solomon Islands is not associated with IgG antibody response to the gSG6 salivary protein of Anopheles gambiae.

BACKGROUND: Mosquito saliva elicits immune responses in humans following mosquito blood feeding. Detection of human antibodies recognizing the Anopheles gambiae salivary gland protein 6 (gSG6) or the gSG6-P1 peptide in residents of Africa, South America and Southeast Asia suggested the potential for these antibodies to serve as a universal marker to estimate human biting rates. Validating the utility of this approach requires concurrent comparisons of anopheline biting rates with antibodies to the gSG6 protein to determine the sensitivity and specificity of the assay for monitoring changes in vector populations. This study investigated whether seroprevalence of anti-gSG6 antibodies in humans reflected the relative exposure to Anopheles farauti bites in the Solomon Islands as estimated from sympatric human landing catches. METHODS: Human biting rates by An. farauti were estimated by landing catches at 10 sampling sites in each of 4 villages during the wet and dry seasons. Human serum samples from these same villages were also collected during the wet and dry seasons and analysed for antibody recognition of the gSG6 antigen by the Luminex xMAP© platform. Antibody titres and prevalence were compared to HLCs at the sampling sites nearest to participants' residences for utility of anti-gSG6 antibodies to estimate human exposure to anopheline bites. RESULTS: In this study in the Solomon Islands only 11% of people had very high anti-gSG6 antibody titres, while other individuals did not recognize gSG6 despite nightly exposures of up to 190 bites by An. farauti. Despite clear spatial differences in the human biting rates within and among villages, associations between anti-gSG6 antibody titres and biting rates were not found. CONCLUSIONS: Few studies to date have concurrently measured anopheline biting rates and the prevalence of human antibodies to gSG6. The lack of association between anti-gSG6 antibody titres and concurrently measured human biting rates suggests that the assay for human anti-gSG6 antibodies lacks sufficient sensitivity to be a biomarker of An. farauti exposure at an epidemiologically relevant scale. These findings imply that an improvement in the sensitivity of serology to monitor changes in anopheline biting exposure may require the use of saliva antigens from local anophelines, and this may be especially true for species more distantly related to the African malaria vector An. gambiae.

Maximising mosquito collections from barrier screens: the impacts of physical design and operation parameters.

BACKGROUND: Traditional methods for collecting outdoor resting mosquitoes are generally inefficient with relatively low numbers caught per unit effort. The barrier screen, designed to intercept mosquitoes as they fly between areas where blood meals are obtained and oviposition sites where eggs are laid, was developed in 2013 as a novel method of sampling outdoor mosquito populations. Barrier screens do not use an odorant lure and are thus a non-mechanical, simple, low maintenance and passive sampling method for use, even in isolated locations. METHODS: To maximise mosquito collections from barrier screens, multiple Latin square 3 × 3 experiments were conducted in Smithfield, Queensland, Australia. Parameters of barrier screens were varied including the effects of construction materials (net weight and colour), screen design and frequency of inspections. RESULTS: Significantly more mosquitoes were collected on simple dark coloured screens of 50% or 70% shading weight with collections every 30 min. Sixty percent of mosquitoes were found on barrier screens within 60 cm of the ground. CONCLUSIONS: The barrier screen is a relatively new adaptable tool that can answer a number of behavioural, ecological and epidemiological questions relevant for the surveillance and basic understanding of the movement and resting habits of mosquitoes by sex or physiological status. This method has demonstrated robustness in collecting a wide range of mosquito species as well as flexibility in where barrier screens can be deployed to explore mosquito movements within rural and peri-domestic environments.

Genetic background influences UPR but not PLP processing in the rumpshaker model of PMD/SPG2.

Mutations of the proteolipid protein gene (PLP1) cause Pelizaeus-Merzbacher disease (PMD) and Spastic paraplegia type 2 (SPG2). The rumpshaker mutation is associated with mild forms of PMD or SPG2 in man and the identical mutation occurs in mice, the phenotype depending on genetic background. The mild phenotype in C3H mice becomes a lethal disease when expressed on the C57BL/6 background. rumpshaker PLP is synthesised at a similar rate to wild type but is rapidly degraded by the proteasome. We show that the rates of synthesis, degradation and myelin incorporation of PLP/DM20 are similar in mutants on both backgrounds and therefore differences in PLP processing are unlikely to be the basis of the phenotypic variation. An unfolded protein response (UPR) is activated in rumpshaker. Whereas activation of CHOP correlates with phenotypic severity, we find no difference in the response of BiP and X-box protein1 (Xbp1) between the two strains.

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid-mediated excitotoxic axonal damage is attenuated in the absence of myelin proteolipid protein.

In vivo and in vitro studies have shown that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated excitotoxicity causes cytoskeletal damage to axons. AMPA/kainate receptors are present on oligodendrocytes and myelin, but currently there is no evidence to suggest that axon cylinders contain AMPA receptors. Proteolipid protein (PLP) and DM20 are integral membrane proteins expressed by CNS oligodendrocytes and located in compact myelin. Humans and mice lacking normal PLP/DM20 develop axonal swellings and degeneration, suggesting that local interactions between axons and the oligodendrocyte/myelin unit are important for the normal functioning of axons and that PLP/DM20 is involved in this process. To determine whether perturbed glial-axonal interaction affects AMPA-receptor-mediated axonal damage, AMPA (1.5 nmol) was injected into the caudate nucleus of anesthetized Plp knockout and wild-type male mice (n = 13). Twenty-four hours later, axonal damage was detected by using neurofilament 200 (NF 200) immunohistochemistry and neuronal damage detected via histology. AMPA-induced axonal damage, assessed with NF 200 immunohistochemistry, was significantly reduced in Plp knockout mice compared with wild-type mice (P = 0.015). There was no significant difference in the levels of neuronal perikaryal damage between the Plp knockout and wild-type mice. In addition, there was no significant difference in the levels of glutamate receptor subunits GluR1-4 or KA2 in Plp knockout compared with wild-type littermates. The present study suggests that PLP-mediated interactions among oligodendrocytes, myelin, and axons may be involved in AMPA-mediated axonal damage.

The myelinated axon is dependent on the myelinating cell for support and maintenance: molecules involved.

The myelin-forming cells, oligodendrocytes and Schwann cells, extend processes that spirally wrap axons and provide the insulation that allows rapid saltatory conduction. Recent data suggest a further role for the myelin-forming cells in axonal support and maintenance. This Mini-Review summarises some of the data that support this view and highlights the molecules involved.

Age-related axonal and myelin changes in the rumpshaker mutation of the Plp gene.

The PLP1/Plp gene encodes proteolipid protein (PLP) and DM20, the major central nervous system myelin proteins. Mutations in the PLP1/ Plp gene cause dysmyelinating disorders in man and animals. The rumpshaker mutation was first identified in mice and later linked to a family diagnosed with neurological deficits akin to spastic paraplegia. The dysmyelination in the young rumpshaker mouse is well characterised. Here we report evidence for an age-related increase in myelin due mainly to the myelination of small axons, many large axons remain dysmyelinated. Levels of PLP/DM20 and myelin basic protein are considerably greater in myelin fractions from older compared with younger mutants. Myelin in sheaths of larger axons remains poorly compacted and may account for levels of 2',3'-cyclic nucleotide 3'-phosphodiesterase and myelin-associated glycoprotein being elevated over wild type in older mutant mice. A late-onset distal degeneration of the axons of the longest spinal tract, the fasciculus gracilis, is also noted. This is the first report of Wallerian-type degeneration in mice with spontaneous mutations of the Plp gene.

Phenotypic analysis of mice deficient in the major myelin protein MOBP, and evidence for a novel Mobp isoform.

Myelin-associated oligodendrocytic basic protein (MOBP) is a recently identified major component of central nervous system (CNS) myelin. We previously reported a detailed characterization of the genomic region encompassing the Mobp gene, elucidating the complex series of transcript splicing responsible for the generation of its diverse family of protein isoforms. These basic, positively charged polypeptides display spatial and temporal expression patterns consistent with a potential role in the compaction and maintenance of the myelin sheath. MOBP isoforms have also been localized to the nucleus and the microtubular network of oligodendrocytes; transcript corresponding to one isoform is present during embryonic development. Recent reports have identified a role for this protein family in the pathogenesis of multiple sclerosis, but a clear function for the wild-type protein has remained unclear. We report a detailed analysis of a targeted mutation of Mobp, which results in the deletion of the translational start site and most of the coding sequence of MOBP, and the deletion of the entire coding sequence corresponding to a novel, putative MOBP isoform. Our analyses clearly demonstrate that MOBP-deficient mice develop normally, generate intact compact CNS myelin, and demonstrate no obvious clinical phenotype. Furthermore, in contrast with another recent study, we find that Mobp null mice demonstrate no significant influence on the axonal diameter of myelinated axons. Although MOBP is not essential for myelination, it appears that its absence is not simply compensated for by increased expression of the "classic" myelin basic protein (MBP).

Survival of, and competition between, oligodendrocytes expressing different alleles of the Plp gene.

Mutations in the X-linked Plp gene lead to dysmyelinating phenotypes and oligodendrocyte cell death. Here, we exploit the X inactivation phenomenon to show that a hierarchy exists in the influence of different mutant Plp alleles on oligodendrocyte survival. We used compound heterozygote mice to study the long-term fate of oligodendrocytes expressing either the jimpy or rumpshaker allele against a background of cells expressing a Plp-null allele. Although mutant and null oligodendrocytes were generated in equal numbers, the proportion expressing the mutant allele subsequently declined, but whereas those expressing the rumpshaker allele formed a reduced but stable population, the number of jimpy cells fell progressively. The age of decline in the jimpy cells in different regions of the CNS correlated with the temporal sequence of myelination. In compound heterozygotes expressing rumpshaker and jimpy alleles, oligodendrocytes expressing the former predominated and were more abundant than when the rumpshaker and null alleles were in competition. Thus, oligodendrocyte survival is not determined solely by cell intrinsic factors, such as the conformation of the misfolded PLP, but is influenced by neighboring cells, possibly competing for cell survival factors.

The fates of cells generated at the end of neurogenesis in developing mouse cortex.

Most cerebral cortical neurons are generated between embryonic days 11 and 17 (E11-17) in the mouse. Radial glial cells also proliferate during this time; they can give rise to neurons and many later transform into astrocytes. It is thought that most glial cells comprising the mature cortex, including additional astrocytes, are generated after neurogenesis is complete. Little is known about the cellular events that occur during the transition from the phase dominated by neurogenesis to that of gliogenesis. We labeled cells generated on E18 and E19 and the day of birth (P0) with bromodeoxyuridine and followed their fates over the following 20 days. Our results showed that, on E18-P0, cells divide throughout the ventricular zone, subventricular zone, intermediate zone, and to a lesser extent, the developing cortical plate, whereas neuronal precursors generated prior to E18 divide in the ventricular zone. Our results indicated that 30-40% of cells dividing on E18 give rise to neurons that migrate to the most superficial part of the cortex. The rest of the cells dividing on E18 and 76-94% of cells generated on E19 and P0 express the QKI RNA-binding protein, indicating that they either remain as multipotential progenitors or develop into glial cells. Nine to fifteen percent of cells generated on E18-P0 become glial fibrillary acidic protein-positive astrocytes. Many E19 and P0 labeled cells disappear between 2 and 20 days postlabeling, probably because they continue to divide. We conclude that the population of cells produced at the end of cortical neurogenesis is heterogeneous and comprises postmitotic neurons, glia (including astrocytes), and possibly multipotential progenitors.

Radial migration in the cerebral cortex is enhanced by signals from thalamus.

The six layered cerebral cortex derives from cells that divide in the ventricular zone and migrate to their final destination in the cortical plate (future cortex). In the mouse, cortical layer III and IV neurons undergo their final mitotic division at around E16, at which time thalamic axons are beginning to enter the cortex. We used bromodeoxyuridine-birth dating of cells in cortical slice cultures to show that the thalamus enhances the migration out of the ventricular zone of future layer III/IV cells. When cortical slices were cultured alone, less than 35% of cells born in vitro on E16 were present in the pial half of the slice after 48 h in culture. In contrast, when cortical slices were cocultured with thalamus, 69% of these cells were found in the pial half of the slice. Explants of other developing tissues did not mimic the effect of the thalamus. The thalamus had no obvious effect on cortical radial glial cells, cortical cell viability or maintenance of cortical slice structure. We found that most precursors born at a similar age but in vivo, shortly before cortical slices were isolated, migrated to the pial half of the cultured slices in the absence of a cocultured thalamic explant. Thus, E16 cortical slices cultured without thalamus permit migration of cells born in vivo and therefore already exposed to the thalamus. Our results indicate that the thalamus provides factors to E16-born cortical precursors that enhance their directed migration out of the ventricular zone to the cortical plate.

A role for Pax6 in the normal development of dorsal thalamus and its cortical connections.

The transcription factor Pax6 is widely expressed throughout the developing nervous system, including most alar regions of the newly formed murine diencephalon. Later in embryogenesis its diencephalic expression becomes more restricted. It persists in the developing anterior thalamus (conventionally termed "ventral" thalamus) and pretectum but is downregulated in the body of the posterior (dorsal) thalamus. At the time of this downregulation, the dorsal thalamus forms its major axonal efferent pathway via the ventral telencephalon to the cerebral cortex. This pathway is absent in mice lacking functional Pax6 (small eye homozygotes: Sey/Sey). We tested whether the mechanism underlying this defect includes abnormalities of the dorsal thalamus itself. We exploited a new transgenic mouse ubiquitously expressing green fluorescent protein tagged with tau, in which axonal tracts are clearly visible, and co-cultured dorsal thalamic explants from Pax6(+/+ )or Pax6(Sey/Sey )embryos carrying the transgene with wild-type tissues from other regions of the forebrain. Whereas Pax6(+/+ )thalamic explants produced strong innervation of wild-type ventral telencephalic explants in a pattern that mimicked the thalamocortical tract in vivo, Pax6(Sey)(/Sey) explants did not, indicating a defect in the ability of mutant dorsal thalamic cells to respond to signals normally present in ventral telencephalon. Pax6(Sey)(/Sey) embryos also showed early alterations in the expression of regulatory genes in the region destined to become dorsal thalamus. Whereas in normal mice Nkx2.2 and Lim1/Lhx1 are expressed ventral to this region, in the mutants their expression domains are throughout it, suggesting that a primary action of Pax6 is to generate correct dorsoventral patterning in the diencephalon. Our results suggest that normal thalamocortical development requires the actions of Pax6 within the dorsal thalamus itself.

The proteolipid protein gene and myelin disorders in man and animal models.

The two proteins, proteolipid protein and DM20, which are encoded by alternative transcripts from the proteolipid protein ( PLP ) gene, are major components of central nervous system myelin. In man, mutations of these proteins cause Pelizaeus-Merzbacher disease (PMD), an X-linked dysmyelinating neuropathy. The mutations found are very varied, ranging from deletions, loss-of-function and missense mutations to additional copies of the gene. This same range of known genetic defects has been observed in animal models with spontaneous and engineered Plp gene mutations. The relationship between genotype and phenotype is remarkably close in the animal models and the PMD cases, making them useful models for studying the mechanisms of PLP gene-related disease. As a result, it has become clear that the PLP gene plays a wider role in neural development in addition to its function as a structural component of myelin. It has also emerged that duplications of the PLP gene are the commonest mutation in PMD. Genetic disorders arising from a dosage effect may be more common than previously recognized. The study of the PLP gene in this rare disorder is, therefore, contributing both to our understanding of neural development and maintenance and to the mechanisms of human genetic disorders.