Dawson-Scully, Ken

RanBP9 is known to act as a scaffolding protein bringing together a variety of cell surface receptors and intracellular targets
thereby regulating functions as diverse as neurite and axonal outgrowth, cell morphology, cell proliferation, myelination,
gonad development, myofibrillogenesis and migration of neuronal precursors. Though RanBP9 is ubiquitously expressed in
all tissues, brain is one of the organs with the highest expression levels of RanBP9. In the neurons, RanBP9 is localized mostly
in the cytoplasm but also in the neurites and dendritic processes. We recently demonstrated that RanBP9 plays pathogenic
role in Alzheimer’s disease. To understand the role of RanBP9 in the brain, here we generated RanBP9 null mice by genetrap
based strategy. Most of Ran-/- mice die neonatally due to defects in the brain growth and development. The major
defects include smaller cortical plate (CP), robustly enlarged lateral ventricles (LV) and reduced volume of hippocampus (HI).
The lethal phenotype is due to a suckling defect as evidenced by lack of milk in the stomachs even several hours after
parturition. The complex somatosensory system which is required for a behavior such as suckling appears to be
compromised in Ran-/- mice due to under developed CP. Most importantly, RanBP9 phenotype is similar to ERK1/2
double knockout and the neural cell adhesion receptor, L1CAM knockout mice. Both ERK1 and L1CAM interact with RanBP9.
Thus, RanBP9 appears to control brain growth and development through signaling mechanisms involving ERK1 and L1CAM
receptor.

While the mammalian brain functions within a very narrow range of oxygen concentrations
and temperatures, the fruit fly, Drosophila melanogaster, has employed strategies to deal
with a much wider range of acute environmental stressors. The foraging (for) gene encodes
the cGMP-dependent protein kinase (PKG), has been shown to regulate thermotolerance
in many stress-adapted species, including Drosophila, and could be a potential therapeutic
target in the treatment of hyperthermia in mammals. Whereas previous thermotolerance
studies have looked at the effects of PKG variation on Drosophila behavior or excitatory
postsynaptic potentials at the neuromuscular junction (NMJ), little is known about PKG
effects on presynaptic mechanisms. In this study, we characterize presynaptic calcium
([Ca^2+]i) dynamics at the Drosophila larval NMJ to determine the effects of high temperature
stress on synaptic transmission. We investigated the neuroprotective role of PKG modulation
both genetically using RNA interference (RNAi), and pharmacologically, to
determine if and how PKG affects presynaptic [Ca^2+]i dynamics during hyperthermia. We
found that PKG activity modulates presynaptic neuronal Ca^2+ responses during acute
hyperthermia, where PKG activation makes neurons more sensitive to temperatureinduced
failure of Ca^2+ flux and PKG inhibition confers thermotolerance and maintains normal
Ca^2+ dynamics under the same conditions. Targeted motoneuronal knockdown of PKG
using RNAi demonstrated that decreased PKG expression was sufficient to confer thermoprotection.
These results demonstrate that the PKG pathway regulates presynaptic motoneuronal
Ca^2+ signaling to influence thermotolerance of presynaptic function during acute
hyperthermia.

Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to
more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the
effects of energetic compromise in Drosophila by targeting the Na+/K+-ATPase. Acute ouabain treatment of intact flies
resulted in subsequent repetitive comas that led to death and were associated with transient loss of K+ homeostasis in the
brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion
homeostasis we subjected flies to repetitive anoxia while recording extracellular [K+] in the brain. We show that targeted
expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with
repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.

Drosophila melanogaster is a promiscuous species that inhabits a large range of harsh environments
including flooded habitats and varying temperature changes. To survive these environments, fruit flies have
adapted mechanisms of tolerance that allow them to thrive. During exposure to anoxic stress, fruit flies and
other poikilotherms enter into a reversible, protective coma. This coma can be manipulated based on
controlled environmental conditions inside the laboratory. Here we utilize a common laboratory raised
strain of D. melanogaster to characterize adaptation abilities to better understand coma recovery and
survival limitations. Our goal is to mimic the fly’s natural environments (wet anoxia) and relate findings to a
typical gas induced environment (dry anoxia) that is commonly used in a laboratory. Despite the abundance
of research regarding acute and chronic anoxic exposure and cold stress, the literature is lacking evidence
linking anoxic stress with variable environmental conditions such as animal age and stress duration. We
present novel ways to assess coma recovery and survival using readily available laboratory tools. Our
findings suggest that younger age, exposure to colder temperatures and wet environments increase
resistance to anoxic stress.