Neural-Specific Inactivation of ShcA Results in Increased Embryonic Neural Progenitor Apoptosis and Microencephaly

Department of Pathology (Neuropathology), Beirne B. Carter Center for Immunology Research, University of Virginia, Charlottesville, Virginia 22908, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 08/2006; 26(30):7885-97. DOI: 10.1523/JNEUROSCI.3524-05.2006
Source: PubMed


Brain size is precisely regulated during development and involves coordination of neural progenitor cell proliferation, differentiation, and survival. The adapter protein ShcA transmits signals from receptor tyrosine kinases via MAPK (mitogen-activated protein kinase)/ERK (extracellular signal-regulated kinase) and PI3K (phosphatidylinositol 3-kinase)/Akt signaling pathways. In the CNS, ShcA expression is high during embryonic development but diminishes as cells differentiate and switches to ShcB/Sck/Sli and ShcC/N-Shc/Rai. To directly test ShcA function in brain development, we used Cre/lox technology to express a dominant-negative form of ShcA (ShcFFF) in nestin-expressing neural progenitors. ShcFFF-expressing mice display microencephaly with brain weights reduced to 50% of littermate controls throughout postnatal and adult life. The cerebrum appeared most severely affected, but the gross architecture of the brain is normal. Body weight was mildly affected with a delay in reaching mature weight. At a mechanistic level, the ShcFFF microencephaly phenotype appears to be primarily attributable to elevated apoptosis levels throughout the brain from embryonic day 10.5 (E10.5) to E12, which declined by E14.5. Apoptosis remained at normal basal levels throughout postnatal development. Proliferation indices were not significantly altered in the embryonic neuroepithelium or within the postnatal subventricular zone. In another approach with the same nestin-Cre transgene, conditional deletion of ShcA in mice with a homozygous floxed shc1 locus also showed a similar microencephaly phenotype. Together, these data suggest a critical role for ShcA in neural progenitor survival signaling and in regulating brain size.

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    • "Previous studies do not report obvious macroscopic neuroanatomical alterations in KO mice, indicating that only the lack of the p46 and/or p52 isoforms lead to microcephaly, but not ablation of p66 Shc (Migliaccio et al., 1999; McFarland et al., 2006). Although not comparable with the microcephaly induced by other isoforms, the reduction in brain size found in the p66 Shc KO mice here supports a neurodevelopmental defect, suggesting that p66 Shc KO effects extend beyond the hippocampus. "
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    ABSTRACT: Aging is accompanied by poor learning and memory abilities and by decreased hippocampal neurogenesis, a process that is also modulated by oxidative stress (OS). P66(Shc) has recently emerged as a novel mammalian gerontogene able to affect healthspan during aging. Deletion of this gene in mice leads to reduced OS accompanied by decreased incidence of age-related pathologies and reduced signs of behavioral aging. We hypothesized that p66(Shc-/-) mutants might show increased neurogenesis in the hippocampus, a brain region involved in learning and memory processes. To this aim, granule cell number, proliferation, neuronal differentiation, and cell death were assessed in the hippocampus in senescent p66(Shc-/-) [knock out (KO)] and p66(Shc+/+) [wild type (WT)] male and female mice. Spatial learning abilities and spontaneous activity were also investigated in a multifunctional behavioral system-IntelliCages. The behavioral analysis revealed that females in general perform better in spatial learning tasks, with genotype effects being apparent in the activity pattern only. Likewise, all females showed increased neuronal differentiation, whereas increased proliferation was found only in those belonging to the p66(Shc-/-) genotype, indicating that they might be protected from precursor cell loss. The number of dying cells was not affected by genotype or sex; however, all KO mice showed less granule cells than WT. Overall, our data suggest that hippocampal function is protected in the female gender at older age, an effect amplified by reduced OS in the p66(Shc-/-) mutant. © 2012 Wiley Periodicals, Inc.
    Full-text · Article · Dec 2012 · Hippocampus
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    • "In these animals, the Nestin second intronic /promoter enhancer drives the expression of beta-galactosidase (β-gal) to neural precursors throughout the developing and mature nervous system. Although these animals are often employed to target inducible gene expression to Nestin-positive neural stem cells (Lardelli et al., 1996; McFarland et al., 2006), we employed the beta-galactosidase marker to identify cells with stem cell potential. The goal of the present study was to determine if Nestin positive cells were present in the developing and mature cochlea and to investigate the response of these cells to an insult that stresses the auditory epithelium and causes limited elimination of cochlear hair cell. "
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    ABSTRACT: The auditory sensory epithelium in non-mammalian vertebrates can replace lost hair cells by transdifferentiation of supporting cells, but this regenerative ability is lost in the mammalian cochlea. Future cell-based treatment of hearing loss may depend on stem cell transplantation or on transdifferentiation of endogenous cells in the cochlea. For both approaches, identification of cells with stem cell features within the mature cochlea may be useful. Here we use a Nestin-β-gal mouse to examine the presence of Nestin positive cells in the mature auditory epithelium, and determine how overstimulation of the ear impacts these cells. Nestin positive cells were found in the apical turn of the cochlea lateral to the outer hair cell area. This pattern of expression persisted into mature age. The area of Nestin positive cells was increased after the noise lesion. This increase in area coincided with an increase in expression of the Nestin mRNA. The data suggest that cells with potential stem cell features remain in the mature mammalian cochlea, restricted to the apical turn, and that an additional set of signals is necessary to trigger their contribution to cell replacement therapy in the ear. As such, this population of cells could serve to generate cochlear stem cells for research and potential therapy, and may be a target for treatments based on induced transdifferentiation of endogenous cochlear cells.
    Full-text · Article · Nov 2011 · Molecular and Cellular Neuroscience
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    • "The final outcome is a brain of the correct size, where neurons that make their proper connections survive. In a number of gene knockout mice, defective proliferation or apoptosis has been related to abnormal development of the brain (Camarero et al., 2006; Cappello et al., 2006; Ke et al., 2007; Klezovitch et al., 2004; McFarland et al., 2006; Tomita et al., 2003; Zhang et al., 2006). Pak4 has been implicated in both cell proliferation and resistance to apoptosis (Gnesutta and Minden, 2003; Gnesutta et al., 2001; Li and Minden, 2005; Liu et al., 2008; Qu et al., 2001). "
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    ABSTRACT: The Pak4 serine/threonine kinase regulates cytoskeletal organization, and controls cell growth, proliferation, and survival. Deletion of Pak4 in mice results in embryonic lethality prior to embryonic day 11.5. Pak4 knockout embryos exhibit abnormalities in the nervous system, the heart, and other tissues. In this study a conditional deletion of Pak4 was generated in order to study the function of Pak4 in the development of the brain. Nervous system-specific conditional deletion of Pak4 was accomplished by crossing mice with a floxed allele of Pak4 with transgenic mice expressing Cre recombinase under the control of the nestin promoter. The conditional Pak4 knockout mice were born normally, but displayed growth retardation and died prematurely. The brains showed a dramatic decrease in proliferation of cortical and striatal neuronal progenitor cells. In vitro analyses revealed a reduced proliferation and self-renewing capacity of neural progenitor cells isolated from Pak4 knockout brains. The mice also exhibited cortical thinning, impaired neurogenesis and loss of neuroepithelial adherens junctions. By the time the mice died, by 4weeks after birth, severe hydrocephalus could also be seen. These results suggest that Pak4 plays a critical role in the regulation of neural progenitor cell proliferation and in establishing the foundation for development of the adult brain.
    Preview · Article · Mar 2011 · Developmental Biology
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