Developmental changes in expression of inhibitory neuronal proteins in the Fragile X Syndrome mouse basolateral amygdala.

In humans, Fragile X Syndrome (FXS) is characterized by enhanced fear, hyperactivity, social anxiety, and, in a subset of individuals, autism. Many of the emotional and social deficits point to defects in the amygdala. We have previously shown defects in inhibitory neuron drive onto excitatory projection neurons in the basolateral amygdala (BLA) of juvenile Fmr1(-/y) knockout (KO) mice. Using pharmacological approaches, we have also previously revealed dynamic functional deficits in α1, α2, and α3 subunit-containing GABAA receptors (GABAARs α1, α2, and α3) during early postnatal development. In this study, we sought to determine whether these defects in GABAAR function are accompanied by changes in protein expression of GABAARs α1, α2, and α3 and the post-synaptic GABAAR-clustering protein gephyrin. Interestingly, we found that while the expression of these proteins did not significantly differ between wildtype (WT) and KO mice at each time point, the timing of developmental expression of GABAAR α1, α2, and gephyrin was altered. Collectively, these data reveal novel defects in inhibitory synapse protein expression during critical periods of early postnatal development that could contribute to observed inhibitory neurotransmission deficits in the KO mouse BLA.

Homeostatic responses fail to correct defective amygdala inhibitory circuit maturation in fragile X syndrome.

Fragile X syndrome (FXS) is a debilitating neurodevelopmental disorder thought to arise from disrupted synaptic communication in several key brain regions, including the amygdala, a central processing center for information with emotional and social relevance. Recent studies reveal defects in both excitatory and inhibitory neurotransmission in mature amygdala circuits in Fmr1(-/y) mutants, the animal model of FXS. However, whether these defects are the result of altered synaptic development or simply faulty mature circuits remains unknown. Using a combination of electrophysiological and genetic approaches, we show the development of both presynaptic and postsynaptic components of inhibitory neurotransmission in the FXS amygdala is dynamically altered during critical stages of neural circuit formation. Surprisingly, we observe that there is a homeostatic correction of defective inhibition, which, despite transiently restoring inhibitory synaptic efficacy to levels at or beyond those of control, ultimately fails to be maintained. Using inhibitory interneuron-specific conditional knock-out and rescue mice, we further reveal that fragile X mental retardation protein function in amygdala inhibitory microcircuits can be segregated into distinct presynaptic and postsynaptic components. Collectively, these studies reveal a previously unrecognized complexity of disrupted neuronal development in FXS and therefore have direct implications for establishing novel temporal and region-specific targeted therapies to ameliorate core amygdala-based behavioral symptoms.

Activated EGFR signaling increases proliferation, survival, and migration and blocks neuronal differentiation in post-natal neural stem cells.

Recent evidence supports the notion that transformation of undifferentiated neural stem cell (NSC) precursors may contribute to the development of glioblastoma multiforme (GBM). The over-expression and mutation of the epidermal growth factor receptor (EGFR), along with other cellular pathway mutations, plays a significant role in GBM maintenance progression. Though EGFR signaling is important in determining neural cell fate and conferring astrocyte differentiation, there is a limited understanding of its role in NSC and tumor stem cell (TSC) biology. We hypothesized that EGFR expression and mutation in post-natal NSCs may contribute to cellular aggressiveness including enhanced cellular proliferation, survival and migration. Stable subclones of C17.2 murine NSCs were transfected to over-express either the wild-type EGFR (wtEGFR) or its most common mutated variant EGFRvIII. Activated EGFR signaling in these cells induced behaviors characteristic of GBM TSCs, including enhanced proliferation, survival and migration, even in the absence of EGF ligand. wtEGFR activation was also found to block neuronal differentiation and was associated with a dramatic increase in chemotaxis in the presence of EGF. EGFRvIII expression lead to an increase in NSC proliferation and survival, while it simultaneously blocked neuronal differentiation and promoted glial fate. Our findings suggest that activated EGFR signaling enhances the aggressiveness of NSCs. Understanding the regulatory mechanisms of NSCs may lend insight into deregulated mechanisms of GBM TSC invasion, proliferation, survival and resistance to current treatment modalities.

Mitogen-activated protein kinase ERK1/2 regulates the class II transactivator.

The expression of major histocompatibility class II genes is necessary for proper antigen presentation and induction of an immune response. This expression is initiated by the class II transactivator, CIITA. The establishment of the active form of CIITA is controlled by a series of post-translational events, including GTP binding, ubiquitination, and dimerization. However, the role of phosphorylation is less clearly defined as are the consequences of phosphorylation on CIITA activity and the identity of the kinases involved. In this study we show that the extracellular signal-regulated kinases 1 and 2 (ERK1/2) interact directly with CIITA, targeting serine residues in the amino terminus of the protein, including serine 288. Inhibition of this phosphorylation by dominant-negative forms of ERK or by treatment of cells with the ERK inhibitor PD98059 resulted in the increase in CIITA-mediated gene expression from a class II promoter, enhanced the nuclear concentration of CIITA, and impaired its ability to bind to the nuclear export factor, CRM1. In contrast, inhibition of ERK1/2 activity had little effect on serine-to-alanine mutant forms of CIITA. These data suggest a model whereby ERK1/2-mediated phosphorylation of CIITA down-regulates CIITA activity by priming it for nuclear export, thus providing a means for cells to tightly regulate the extent of antigen presentation.