Kelly A. Glendining

Queen pheromone modulates brain dopamine function in worker honey bees

Honey bee queens produce a sophisticated array of chemical signals (pheromones) that influence both the behavior and physiology of their nest mates. Most striking are the effects of queen mandibular pheromone (QMP), a chemical blend that induces young workers to feed and groom the queen and primes bees to perform colony-related tasks. But how does this pheromone operate at the cellular level? This study reveals that QMP has profound effects on dopamine pathways in the brain, pathways that play a central role in behavioral regulation and motor control. In young worker bees, dopamine levels, levels of dopamine receptor gene expression, and cellular responses to this amine are all affected by QMP. We identify homovanillyl alcohol as a key contributor to these effects and provide evidence linking QMP-induced changes in the brain to changes at a behavioral level. This study offers exciting insights into the mechanisms through which QMP operates and a deeper understanding of the queens ability to regulate the behavior of her offspring.

Ten_m3 regulates eye-specific patterning in the mammalian visual pathway and is required for binocular vision.

Binocular vision requires an exquisite matching of projections from each eye to form a cohesive representation of the visual world. Eye-specific inputs are anatomically segregated, but in register in the visual thalamus, and overlap within the binocular region of primary visual cortex. Here, we show that the transmembrane protein Ten_m3 regulates the alignment of ipsilateral and contralateral projections. It is expressed in a gradient in the developing visual pathway, which is consistently highest in regions that represent dorsal visual field. Mice that lack Ten_m3 show profound abnormalities in mapping of ipsilateral, but not contralateral, projections, and exhibit pronounced deficits when performing visually mediated behavioural tasks. It is likely that the functional deficits arise from the interocular mismatch, because they are reversed by acute monocular inactivation. We conclude that Ten_m3 plays a key regulatory role in the development of aligned binocular maps, which are required for normal vision.

Maternal Obesity and IL-6 Lead to Aberrant Developmental Gene Expression and Deregulated Neurite Growth in the Fetal Arcuate Nucleus

Maternal obesity during pregnancy increases the risk of obesity in the offspring. Several observations have pointed to a causative role for the proinflammatory cytokine IL-6, but whether it is present in the fetal circulation and how it acts on the developing fetus are unclear. We first observed that postnatal day 0 offspring from obese mothers had significantly reduced neuropeptide Y (NPY) innervation of the paraventricular nucleus (PVN) compared with that for offspring of normal-weight controls. Thus, the growth of NPY neurites from the arcuate nucleus (ARC) was impaired in the fetal brain by maternal obesity. The neurite growth regulator, Netrin-1, was expressed in the ARC and PVN and along the pathway between the two at gestational day (GD) 17.5 in normal animals, making it likely to be involved in the development of NPY ARC-PVN projections. In addition, the expression of Dcc and Unc5d, receptors for Netrin-1, were altered in the GD17.5 ARC in obese but not normal weight pregnancies. Thus, this important developmental pathway is perturbed by maternal obesity and may explain the defect in NPY innervation of the PVN that occurs in fetuses developing in obese mothers. To investigate whether IL-6 may play a role in these developmental changes, we found first that IL-6 was significantly elevated in the fetal and maternal circulation in pregnancies of obese mice compared with those of normal-weight mice. In addition, treatment of GD17.5 ARC tissue with IL-6 in vitro significantly reduced ARC neurite outgrowth and altered developmental gene expression similar to maternal obesity in vivo. These findings demonstrate that maternal obesity may alter the way in which fetal ARC NPY neurons respond to key developmental signals that regulate normal prenatal neural connectivity and suggest a causative role for elevated IL-6 in these changes.

Ten-m3 is required for the development of topography in the ipsilateral retinocollicular pathway.

Background The alignment of ipsilaterally and contralaterally projecting retinal axons that view the same part of visual space is fundamental to binocular vision. While much progress has been made regarding the mechanisms which regulate contralateral topography, very little is known of the mechanisms which regulate the mapping of ipsilateral axons such that they align with their contralateral counterparts. Results Using the advantageous model provided by the mouse retinocollicular pathway, we have performed anterograde tracing experiments which demonstrate that ipsilateral retinal axons begin to form terminal zones (TZs) in the superior colliculus (SC), within the first few postnatal days. These appear mature by postnatal day 11. Importantly, TZs formed by ipsilaterally-projecting retinal axons are spatially offset from those of contralaterally-projecting axons arising from the same retinotopic location from the outset. This pattern is consistent with that required for adult visuotopy. We further demonstrate that a member of the Ten-m/Odz/Teneurin family of homophilic transmembrane glycoproteins, Ten-m3, is an essential regulator of ipsilateral retinocollicular topography. Ten-m3 mRNA is expressed in a high-medial to low-lateral gradient in the developing SC. This corresponds topographically with its high-ventral to low-dorsal retinal gradient. In Ten-m3 knockout mice, contralateral ventrotemporal axons appropriately target rostromedial SC, whereas ipsilateral axons exhibit dramatic targeting errors along both the mediolateral and rostrocaudal axes of the SC, with a caudal shift of the primary TZ, as well as the formation of secondary, caudolaterally displaced TZs. In addition to these dramatic ipsilateral-specific mapping errors, both contralateral and ipsilateral retinocollicular TZs exhibit more subtle changes in morphology. Conclusions We conclude that important aspects of adult visuotopy are established via the differential sensitivity of ipsilateral and contralateral axons to intrinsic guidance cues. Further, we show that Ten-m3 plays a critical role in this process and is particularly important for the mapping of the ipsilateral retinocollicular pathway.

Maternal Obesity in the Mouse Compromises the Blood-Brain Barrier in the Arcuate Nucleus of Offspring.

The arcuate nucleus (ARC) regulates body weight in response to blood-borne signals of energy balance. Blood-brain barrier (BBB) permeability in the ARC is determined by capillary endothelial cells (ECs) and tanycytes. Tight junctions between ECs limit paracellular entry of blood-borne molecules into the brain, whereas EC transporters and fenestrations regulate transcellular entry. Tanycytes appear to form a barrier that prevents free diffusion of blood-borne molecules. Here we tested the hypothesis that gestation in an obese mother alters BBB permeability in the ARC of offspring. A maternal high-fat diet model was used to generate offspring from normal-weight (control) and obese dams (OffOb). Evans Blue diffusion into the ARC was higher in OffOb compared with controls, indicating that ARC BBB permeability was altered. Vessels investing the ARC in OffOb had more fenestrations than controls, although the total number of vessels was not changed. A reduced number of tanycytic processes in the ARC of OffOb was also observed. The putative transporters, Lrp1 and dysferlin, were up-regulated and tight junction components were differentially expressed in OffOb compared with controls. These data suggest that maternal obesity during pregnancy can compromise BBB formation in the fetus, leading to altered BBB function in the ARC after birth.

Congenital mirror movements: Phenotypes associated with DCC and RAD51 mutations

Congenital mirror movements (CMM) is a disorder characterized by unintentional mirroring in homologous motor systems of voluntary movements on the opposite side, usually affecting the distal upper extremities. Genetic analyses have revealed involvement of three genes (DCC, RAD51, and DNAL4). We sought to distinguish whether different phenotypes of CMM exist, and if so, whether they might map to different causative genes. We studied 14 individuals across five families with dominantly-inherited CMM. We used accelerometer gloves to analyse the fine detail of index finger tapping movements, and applied standard genetic methodology to analyse DNA samples. Two forms of mirroring were distinguished: actual in which the mirroring followed precisely the movements of the voluntary hand, and fractionated in which the mirroring was saccadic. We found that actual mirroring was characteristic of individuals in a family with a RAD51 mutation, and fractionated more characteristic of a family with a DCC mutation. These findings are suggestive of specific genotype-phenotype correlations in CMM. Three heterozygous individuals (one RAD51; two DCC) showed no apparent mirroring on visual inspection, although mirroring was detectable with the accelerometer gloves. Thus, subclinical mirroring may be present even when undetectable on clinical observation.

Maternal obesity leads to increased proliferation and numbers of astrocytes in the developing fetal and neonatal mouse hypothalamus

Maternal obesity during pregnancy is associated with chronic maternal, placental, and fetal inflammation; and it elevates the risk for offspring obesity. Changes in the development of the hypothalamus, a brain region that regulates body weight and energy balance, are emerging as important determinants of offspring risk, but such changes are only beginning to be defined. Here we focused on the hypothesis that the pathological exposure of developing hypothalamic astrocytes to cytokines would alter their development.

A novel role for the DNA repair gene Rad51 in Netrin-1 signalling.

Mutations in RAD51 have recently been linked to human Congenital Mirror Movements (CMM), a developmental disorder of the motor system. The only gene previously linked to CMM encodes the Netrin-1 receptor DCC, which is important for formation of corticospinal and callosal axon tracts. Thus, we hypothesised that Rad51 has a novel role in Netrin-1-mediated axon development. In mouse primary motor cortex neurons, Rad51 protein was redistributed distally down the axon in response to Netrin-1, further suggesting a functional link between the two. We next manipulated Rad51 expression, and assessed Netrin-1 responsiveness. Rad51 siRNA knockdown exaggerated Netrin-1-mediated neurite branching and filopodia formation. RAD51 overexpression inhibited these responses, whereas overexpression of the CMM-linked R250Q mutation, a predicted loss-of-function, had no effect. Thus, Rad51 appears to negatively regulate Netrin-1 signalling. Finally, we examined whether Rad51 might operate by modulating the expression of the Unc5 family, known negative regulators of Netrin-1-responsiveness. Unc5b and Unc5c transcripts were downregulated in response to Rad51 knockdown, and upregulated with RAD51 overexpression, but not R250Q. Thus, Rad51 negatively regulates Netrin-1 signalling, at least in part, by modulating the expression of Unc5s. Imbalance of positive and negative influences is likely to lead to aberrant motor system development resulting in CMMs.

Retinal overexpression of Ten-m3 alters ipsilateral retinogeniculate projections in the wallaby (Macropus eugenii)

The dorsal lateral geniculate nucleus (dLGN) contains a retinotopic map where input from the two eyes map in register to provide a substrate for binocular vision. Ten-m3, a transmembrane protein, mediates homophilic interactions and has been implicated in the patterning of ipsilateral visual projections. Ease of access to early developmental stages in a marsupial wallaby has been used to manipulate levels of Ten-m3 during the development of retinogeniculate projections. In situ hybridisation showed a high dorsomedial to low ventrolateral gradient of Ten-m3 in the developing dLGN, matching retinotopically with the previously reported high ventral to low dorsal retinal gradient. Overexpression of Ten-m3 in ventronasal but not dorsonasal retina resulted in an extension of ipsilateral projections beyond the normal binocular zone. These results demonstrate that Ten-m3 influences ipsilateral projections and support a role for it in binocular mapping.

Overexpression of Ten-m3 in the retina alters ipsilateral retinocollicular projections in the wallaby (Macropus eugenii).

Retinal projections to the superior colliculus are organised into retinotopic maps. Binocular vision requires that inputs from the two eyes map in register with each other. Studies in mice lacking Ten‐m3, a homophilic transmembrane protein, indicate that it plays a key role in this process by influencing ipsilateral projections. The postnatal, ex utero development of the wallaby allows the targeted manipulation of molecules of interest during development. The distribution of mRNA for Ten‐m3 in the retina and superior colliculus of the wallaby, and the effects of its spatiotemporally restricted retinal overexpression was investigated, in particular on the mapping of ipsilateral projections. Quantitative polymerase chain reaction found that Ten‐m3 mRNA is expressed at relatively higher levels in the retina and colliculus early in development. Further, it is higher in ventral than dorsal retina, and increased in the retinotopically corresponding medial compared to lateral superior colliculus. In situ hybridisation demonstrated an increasing dorsoventral gradient in retinal ganglion cells was matched to an increasing lateromedial gradient in the superior colliculus. Overexpression of Ten‐m3 by in vivo retinal electroporation produced an increase in ipsilateral projections to the binocular rostromedial colliculus, fitting with the proposal that Ten‐m3 mediates mapping by attractant homophilic interactions. Retrograde labelling of the projection from this region suggested that overexpression produces a shift in the axons of existing ipsilaterally projecting ganglion cells rather than a rerouting of the axons of contralaterally projecting cells. Retinal manipulation of Ten‐m3 levels produces changes in ipsilateral mapping, supporting a role for it in binocular mapping.