Biology subjects

McMillan, L. E.

Publications and source records attributed to McMillan, L. E..

3 recordsLinked to original sources

bioRxiv2020

Friend or foe? Effects of host immune activation on the transient gut microbiome in the caterpillar Manduca sexta

For many animals the gut microbiome plays an essential role in immunity and digestion. However, certain animals, such as the caterpillar Manduca sexta, do not have a resident gut microbiome. Although these animals do have bacteria that pass through their gut from their natural environment, the absence of such bacteria does not reduce growth or survival. We hypothesized that Manduca sexta would sterilize their gut as a protective measure against secondary infection when faced with a gut infection, or exposure to heat-killed bacteria in the blood (hemolymph). However, we found that gut sterilization did not occur during either type of immune challenge, i.e. bacterial numbers did not decrease. By examing the pattern of immune-related gene expression, gut pH, live bacterial counts, and weight change (as a measure of sickness behaviour), we found evidence for physiological trade-offs between between regulating the microbiome and defending against systemic infections. Caterpillars exposed to both gut pathogens and a systemic immune challenge had higher numbers of bacteria in their gut than caterpillars exposed to a single challenge. Following a principal component analysis, we found that the response patterns following an oral challenge, systemic challenge or dual challenge were unique. Our results suggest that the immune response for each challenge resulted in a different configuration of the immunophysiological network. We hypothesize that these different configurations represent different resolutions of physiological trade-offs based on the immune responses needed to best protect against the present immune challenges. SUMMARY STATEMENTThis paper investigates the strategies that animals may use to regulate their microbiome during infection.

immunology↗

bioRxiv2018

Terminal Reproductive Investment, Physiological Trade-offs and Pleiotropic Effects: Their effects produce complex immune/reproductive interactions in the cricket Gryllus texensis

O_LIShould females increase or decrease reproduction when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts an increase in reproduction, but hypothesized physiological trade-offs between reproduction and immune function might be expected to produce a decrease. There is evidence for both hypotheses. What determines the choice between the two responses remains unclear. We examine the effect of age on the reproductive response to immune challenge in long-wing females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (limited) diet.\nC_LIO_LIThe limited diet reduced reproductive output. However, immune challenge had no effect on their reproductive output either in young or middle-aged crickets, which is contrary to either prediction.\nC_LIO_LIFlight muscle maintenance correlated negatively with reproductive output, suggesting a physiological trade-off between flight muscle maintenance and reproduction. Within the long-wing variant there was considerable variability in flight muscle maintenance. This variability may mask physiological trade-offs between immunity and reproduction.\nC_LIO_LIMiddle-aged crickets had higher total phenoloxidase (PO) activity in their hemolymph, compared to young females, which is contrary to the terminal investment theory. Given that PO is involved in both immunity and reproduction, the increased PO may reflect simultaneous investment in both functions.\nC_LIO_LIWe identified four proPO transcripts in a published RNA-seq dataset (transcriptome). Three of the proPO genes were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional); however, the two organs expressed different subsets. The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for immune/reproductive trade-offs in some species.\nC_LIO_LIIncreasing age may not cue terminal reproductive investment prior to senescence.\nC_LI

ecology↗

bioRxiv2018

Transient μm scale protein accumulation at the center of the T cell antigen presenting cell interface drives efficient IL-2 secretion

Supramolecular signaling assemblies are of interest for their unique signaling properties. A {micro}m scale signaling assembly, the central supramolecular signaling cluster (cSMAC), forms at the center of the interface of T cells activated by antigen presenting cells. We have determined that it is composed of multiple complexes of a supramolecular volume of up to 0.5{micro}m3 and associated with extensive membrane undulations. To determine cSMAC function, we have systematically manipulated the localization of three adaptor proteins, LAT, SLP-76, and Grb2. cSMAC localization varied between the adaptors and was diminished upon blockade of the costimulatory receptor CD28 and deficiency of the signal amplifying kinase Itk. Reconstitution of cSMAC localization restored IL-2 secretion which is a key T cell effector function as dependent on reconstitution dynamics. Our data suggest that the cSMAC enhances early signaling by facilitating signaling interactions and attenuates signaling thereafter through sequestration of a more limited set of signaling intermediates.

immunology↗