[show abstract][hide abstract] ABSTRACT: Mice with a complete deficiency of p73 have severe neurological and immunological defects due to the absence of all TAp73 and DeltaNp73 isoforms. As part of our ongoing program to distinguish the biological functions of these isoforms, we generated mice that are selectively deficient for the DeltaNp73 isoform. Mice lacking DeltaNp73 (DeltaNp73(-/-) mice) are viable and fertile but display signs of neurodegeneration. Cells from DeltaNp73(-/-) mice are sensitized to DNA-damaging agents and show an increase in p53-dependent apoptosis. When analyzing the DNA damage response (DDR) in DeltaNp73(-/-) cells, we discovered a completely new role for DeltaNp73 in inhibiting the molecular signal emanating from a DNA break to the DDR pathway. We found that DeltaNp73 localizes directly to the site of DNA damage, can interact with the DNA damage sensor protein 53BP1, and inhibits ATM activation and subsequent p53 phosphorylation. This novel finding may explain why human tumors with high levels of DeltaNp73 expression show enhanced resistance to chemotherapy.
Genes & development 03/2010; 24(6):549-60. · 12.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Asymmetries of multiple components of the rodent cerebrum have been described at various levels of organization. Yet, despite its ubiquitous nature, many confusing and sometimes contradictory reports regarding structural asymmetries in the rodent brain have been published. There is a need, therefore, for a whole-brain imaging analysis technique for asymmetry studies that is both accurate, reproducible and robust. To this end, a comprehensive three-dimensional examination of differences in brain structure in an inbred mouse strain was undertaken. The goal of this study was thus to use high-resolution magnetic resonance imaging to assess structural asymmetries in the adult C57Bl/6J mouse brain. Fixed brain T2-weighted images of 20 male C57Bl/6J mice were acquired on a 7T scanner at 32 microm isotropic resolution. We used voxel-based analyses to examine structural asymmetries throughout the whole mouse brain. The striatum, medial-posterior regions of the thalamus, and motor, sensorimotor, and visual cortex were found to be asymmetrical. The most significant asymmetry was found in the hippocampus and, specifically, the dentate gyrus. In each case, the left region was larger than the right. No other regions of the mouse brain showed structural asymmetry. The results in the dentate gyrus were confirmed using stereology, revealing a correlation of r=0.61 between magnetic resonance and stereological measures. Hippocampal, along with cortical asymmetry, has been discussed repeatedly in the literature, yet a clear pattern of directionality, until this point, has not been described. The findings of asymmetry in the striatum and absence of asymmetry in the rest of the brain are novel and show the advantage of using the whole-brain three-dimensional techniques developed herein for assessing asymmetry.
[show abstract][hide abstract] ABSTRACT: The genetic mechanisms that regulate neurodegeneration are only poorly understood. We show that the loss of one allele of the p53 family member, p73, makes mice susceptible to neurodegeneration as a consequence of aging or Alzheimer's disease (AD). Behavioral analyses demonstrated that old, but not young, p73+/- mice displayed reduced motor and cognitive function, CNS atrophy, and neuronal degeneration. Unexpectedly, brains of aged p73+/- mice demonstrated dramatic accumulations of phospho-tau (P-tau)-positive filaments. Moreover, when crossed to a mouse model of AD expressing a mutant amyloid precursor protein, brains of these mice showed neuronal degeneration and early and robust formation of tangle-like structures containing P-tau. The increase in P-tau was likely mediated by JNK; in p73+/- neurons, the activity of the p73 target JNK was enhanced, and JNK regulated P-tau levels. Thus, p73 is essential for preventing neurodegeneration, and haploinsufficiency for p73 may be a susceptibility factor for AD and other neurodegenerative disorders.