Inhibition of p73 Function by Pifithrin-α as Revealed by Studies in Zebrafish Embryos

The p53 family of proteins contains two members that have been implicated in sensitization of cells and organisms to genotoxic stress, i.e., p53 itself and p73. In vitro, lack of either p53 or p73 can protect certain cell types in the adult organism against death upon exposure to DNA damaging agents. The present study was designed to assess the relative contribution of p53 to radiation resistance of an emerging vertebrate model organism, i.e., zebrafish embryos. Consistent with previous reports, suppressing p53 protein expression using antisense morpholino oligonucleotides (MOs) increased survival and reduced gross morphological alterations in zebrafish embryos exposed to ionizing radiation. By contrast, a pharmacological inhibitor of p53 function [Pifithrin-α (PFTα)] caused developmental abnormalities affecting the head, brain, eyes and kidney function and did not protect against lethal effects of ionizing radiation when administered at 3 hours post fertilization (hpf). The phenotypic abnormalities associated with PFTα treatment were similar to those caused by antisense MO knock down (kd) used to reduce p73 expression. PFTα also inhibited p73-dependent transcription of a reporter gene construct containing canonical p53-responsive promoter sequences. Notably, when administered at later stages of development (23 hpf), PFTα did not cause overt developmental defects but exerted radioprotective effects in zebrafish embryos. In summary, this study highlights off-target effects of the pharmacological p53 inhibitor PFTα related to inhibition of p73 function and essential roles of p73 at early but not later stages of zebrafish development. Abreviations: MO, antisense morpholino oligonucleotide; PFTα, pifithrin-α; Hpf, hours post fertilization; Kd, knock down; IR, ionizing radiation Cell Cycle, Volume 7, Issue 9, pp. 1224-1230

Single genomic enhancers drive experience-dependent GABAergic plasticity to maintain sensory processing in the adult cortex

Experience-dependent plasticity of synapses modulates information processing in neural circuits and is essential for cognitive functions. The genome, via non-coding enhancers, was proposed to control information processing and circuit plasticity by regulating experience-induced transcription of genes that modulate specific sets of synapses. To test this idea, we analyze here the cellular and circuit functions of the genomic mechanisms that control the experience-induced transcription of Igf1 (insulin-like growth factor 1) in vasoactive intestinal peptide (VIP) interneurons (INs) in the visual cortex of adult mice. We find that two sensory-induced enhancers selectively and cooperatively drive the activity-induced transcription of Igf1 to thereby promote GABAergic inputs onto VIP INs and to homeostatically control the ratio between excitation and inhibition (E/I ratio)-in turn, this restricts neural activity in VIP INs and principal excitatory neurons and maintains spatial frequency tuning. Thus, enhancer-mediated activity-induced transcription maintains sensory processing in the adult cortex via homeostatic modulation of E/I ratio