Prenatal viral infection led to altered gene expression in hippocampus at P0, P14, and P56 including schizophrenia and autism candidate genes such as Aqp4, Mbp, Nts, Foxp2, Nrcam, and Gabrg1. qRT-PCR verified the direction and magnitude of change for all of the above genes except for Nrcam. Additionally, qRT-PCR revealed significant changes in a number of other genes including downregulation of myelination genes Mag, Mog, Mobp, Mal, and Plp1 at P0. Morphometric analysis showed a reduction in hippocampal volume at P35. compares gene expression and morphological changes following infection at E9, E16, and E18.
Comparative Effects of Prenatal Viral Infection at E9, E16, and E18 on Gene Expression and Brain Morphology
Interestingly, Foxp2, Mbp and Aqp4 also display altered expression following infection at E9 (; Fatemi et al., 2005
). Additionally, we have observed an upregulation of Foxp2 protein in hippocampus at P14 and P56 following infection at E18 (; Fatemi et al., 2008a
). Foxp2 is a putative transcription factor containing a polyglutamine tract and a forkhead DNA binding domain. Foxp2 is associated with language and speech deficits (Hurst et al., 1990
) that are commonly observed with autism. Aqp4 is localized to astrocytes and ependymal cells in brain and is involved with water transport (Papadopoulos et al., 2002; Verkman et al., 2006
). Aqp4 is also reduced in cerebella of subjects with autism (Fatemi et al., 2008b
). Mbp comprises about 30% of the myelin membrane and is believed to be involved in myelin compaction (Chambers and Perrone-Bizzozero, 2004
). Mbp immunoreactivity is reduced in hippocampi of female subjects with schizophrenia (Chambers and Perrone-Bizzozero, 2004
). Moreover, shiverer mice, which lack Mbp, display delayed action potentials (Lehman and Harrison, 2002
) suggesting a role for Mbp in synaptic transmission. The recurrence of these genes in our data sets at multiple time points and multiple brain regions suggest they may be key to the changes observed following prenatal viral infection.
We demonstrated a 6% reduction in hippocampal volume (p<0.014) at P35 following infection at E16, and have previously demonstrated a 14% reduction in hippocampal volume (p<0.00005) at P35 following infection at E18 (Fatemi et al., 2008
), consistent with the observed reductions in subjects with schizophrenia and autism. We do not have microarray data for this time point following infection at E16 or E18 so it is difficult to determine what genetic factors may play a role in hippocampal atrophy at P35. It is likely, however, that genes related to myelination, growth factors, and synaptic plasticity would be involved. Future studies should include microarray at P35 following infection at these dates. While infection at E18 resulted in morphological changes at P35, infection at E16 resulted in a greater number of changes at various time points as well as a greater number of changes in gene expression () and it is likely that the two linked.
In conclusion, we observed that infection at E16 led to gene expression changes in hippocampi of exposed offspring. There were some similarities in gene expression when compared with infection at E9 and E18 although the total number of genes altered was greater following infection at E16. Moreover, there were a greater number of morphological changes. The greater magnitude of changes at E16 suggests that infection during middle second trimester leads to more deleterious effects in the exposed offspring than during middle first or late second trimester, consistent with findings that infection during middle second trimester carries a greater risk for the development of schizophrenia and autism in humans. These changes are in many cases similar to what has been observed in neuropsychiatric disorders, specifically autism and schizophrenia. Due to a low N, replication of our work is needed to examine the impact of these hippocampal changes in the exposed offspring.