Maternal single injection of N-methyl-N-nitrosourea to cause microcephaly in offspring induces transient aberration of hippocampal neurogenesis in mice

Abstract

N-Methyl-N-nitrosourea (MNU) is an alkylating agent having antiproliferative cytotoxity targeting the neural stem/progenitor cells to cause microcephaly by maternal exposure. This study investigated the effect of transient exposure to MNU on the process of hippocampal neurogenesis in later life using mice. Pregnant mice received a single injection of MNU at 0, 5 and 10mg/kg body weight, intraperitoneally on gestational day 14, and their offspring were examined on postnatal day (PND) 21 and PND 77. On PND 21, offspring displayed microcephaly and hippocampal formation hypoplasia at 10mg/kg, decrease of doublecortin (Dcx)+ cells in the dentate subgranular zone from 5mg/kg, and decrease of TUNEL+ apoptotic cells and increase of transcript expression of anti-apoptotic Bcl-2 at 10mg/kg in the dentate gyrus. In the dentate hilus, numbers of reelin+ or parvalbumin (Pvalb)+ interneurons or neuron-specific nuclear protein+ neurons increased at 10mg/kg. Microcephaly and hippocampal formation hypoplasia continued through PND 77 at 10mg/kg. Thus, apart from the massive cell killing at the migratory stream causing microcephaly, MNU may decrease Dcx+ cells reflecting disruption of the differentiation process of late-stage neuronal progenitors and immature granule cells through defective molecular functions by gene mutations. Increase of reelin+ and Pvalb+ cells may reflect the disruption of neurogenesis and following neuronal migration. All of the granule cell lineage and interneuron changes disappeared at the adult stage on PND 77 suggesting that MNU mainly targets transient populations of highly proliferative progenitor cells but hardly affects their stem cells having self-renewal ability.