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

Abstract

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.

IL-9/IL-9 receptor signaling selectively protects cortical neurons against developmental apoptosis

“…5 In agreement with this time-restricted expression, the IL-9/IL-9R signaling pathway significantly prevented neuronal PCD both in vivo and in vitro. This antiapoptotic effect seemed to similarly affect different cortical areas (motor, somatosensory and visual cortices) but, within each cortical area, to preferentially affect the superficial layers as supported by anticleaved caspase-3 immunostaining and in situ hybridization for IL-9R mRNA.…”

“…[1][2][3][4] Alteration of developmental cell death can be associated with the etiology of several human nervous system abnormalities including hydrocephaly and microcephaly. 1,[5][6][7] The mechanisms of PCD are remarkably conserved among species and the molecular machinery relies on the mitochondrial pathways of intracellular signal transduction. 8,9 For example, null mutations of caspase-3 or caspase-9 in some mouse strains cause an enlarged forebrain due to the lack of normal neural progenitor apoptosis during development.…”

The adaptor protein Shc integrates growth factor and ECM signaling during postnatal angiogenesis

“…11 Interestingly, mice with a conditional deletion of Shc in specific organs such as skeletal muscle, 11 thymocytes, 14 or brain 12 live to adulthood, exhibiting defects only in the function of the tissue in which Shc was removed. Similarly, we now show that endothelial Shc expression is not required for embryonic development, but is required postnatally for angiogenesis.…”

“…More detailed gene-targeting work has shown that the expression of the PTB domain of Shc specifically in cardiomyocytes is critical for midgestational heart development and embryonic life. 11 Conditional knockout strategies have shown that Shc is also important for the proper development/function of other organs such as skeletal muscle, 11 brain, 12 cardiomyocytes, 13 and thymocytes, 14 because tissue-specific deletion of Shc resulted in living but underdeveloped mice. To address the role of Shc in angiogenesis in vivo, we studied loss of Shc function using morpholino (MO) antisense technology in zebrafish.…”

Inducible expression of noggin selectively expands neural progenitors in the adult SVZ

“…The CNS specific intronic enhancer element has been widely employed to drive reporter genes or to target transgene expression to neural stem cells (Lardelli et al, 1996;Panchision et al, 2001;Magdaleno et al, 2002;McFarland et al, 2006;Mills et al, 2006;Walker et al, 2010). Expression of the tetracycline reverse transactivator (rtTA) and cells expressing the nestin transgene was examined by X-gal staining ( Fig.…”