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A small number of offspring are born from the numerous sperm generated from spermatogonial stem cells (SSCs). However, little is known regarding the rules and molecular mechanisms that govern germline transmission patterns. Here we report that the Trp53 tumor suppressor gene limits germline genetic diversity via Cdkn1a. Trp53-deficient SSCs outcompeted wild-type (WT) SSCs and produced significantly more progeny after co-transplantation into infertile mice. Lentivirus-mediated transgenerational lineage analysis showed that offspring bearing the same virus integration were repeatedly born in a non-random pattern from WT SSCs. However, SSCs lacking Trp53 or Cdkn1a sired transgenic offspring in random patterns with increased genetic diversity. Apoptosis of KIT⁺ differentiating germ cells was reduced in Trp53- or Cdkn1a-deficient mice. Reduced CDKN1A expression in Trp53-deficient spermatogonia suggested that Cdkn1a limits genetic diversity by supporting apoptosis of syncytial spermatogonial clones. Therefore, the TRP53-CDKN1A pathway regulates tumorigenesis and the germline transmission pattern.

CHAMP1 is a gene associated with intellectual disability, which was originally identified as being involved in the maintenance of kinetochore–microtubule attachment. To explore the neuronal defects caused by CHAMP1 deficiency, we established mice that lack CHAMP1. Mice that are homozygous knockout for CHAMP1 were slightly smaller than wild-type mice and died soon after birth on pure C57BL/6J background. Although gross anatomical defects were not found in CHAMP1−/− mouse brains, mitotic cells were increased in the cerebral cortex. Neuronal differentiation was delayed in CHAMP1−/− neural stem cells in vitro, which was also suggested in vivo by CHAMP1 knockdown. In a behavioural test battery, adult CHAMP1 heterozygous knockout mice showed mild memory defects, altered social interaction, and depression-like behaviours. In transcriptomic analysis, genes related to neurotransmitter transport and neurodevelopmental disorder were downregulated in embryonic CHAMP1−/− brains. These results suggest that CHAMP1 plays a role in neuronal development, and CHAMP1-deficient mice resemble some aspects of individuals with CHAMP1 mutations.

Our recent study has shown that prenatal exposure to bisphenol A (BPA) altered the expression of genes associated with autism spectrum disorder (ASD). In this study, we further investigated the effects of prenatal BPA exposure on ASD-related genes known to regulate neuronal viability, neuritogenesis, and learning/memory, and assessed these functions in the offspring of exposed pregnant rats. We found that prenatal BPA exposure increased neurite length, the number of primary neurites, and the number of neurite branches, but reduced the size of the hippocampal cell body in both sexes of the offspring. However, in utero exposure to BPA decreased the neuronal viability and the neuronal density in the hippocampus and impaired learning/memory only in the male offspring while the females were not affected. Interestingly, the expression of several ASD-related genes (e.g. Mief2, Eif3h, Cux1, and Atp8a1) in the hippocampus were dysregulated and showed a sex-specific correlation with neuronal viability, neuritogenesis, and/or learning/memory. The findings from this study suggest that prenatal BPA exposure disrupts ASD-related genes involved in neuronal viability, neuritogenesis, and learning/memory in a sex-dependent manner, and these genes may play an important role in the risk and the higher prevalence of ASD in males subjected to prenatal BPA exposure.

The subcommissural organ (SCO) is a part of the circumventricular organs located in the dorsocaudal region of the third ventricle at the entrance of the aqueduct of Sylvius. The SCO comprises epithelial cells and produces high molecular weight glycoproteins, which are secreted into the third ventricle and become part of Reissner's fibre in the cerebrospinal fluid. Abnormal development of the SCO has been linked with congenital hydrocephalus, a condition characterized by excessive accumulation of cerebrospinal fluid in the brain. In the present study, we characterized the SCO cells in the adult mouse brain to gain insights into the possible role of this brain region. Immunohistochemical analyses revealed that expression of Pax6, a transcription factor essential for SCO differentiation during embryogenesis, is maintained in the SCO at postnatal stages from P0 to P84. SCO cells in the adult brain expressed known neural stem/progenitor cell (NSPC) markers, Sox2 and vimentin. The adult SCO cells also expressed proliferating marker PCNA, although expression of another proliferation marker Ki67, indicating a Gsub2/sub/M phase, was not detected. The SCO cells did not incorporate BrdU, a marker for DNA synthesis in the S phase. Therefore, the SCO cells have a potential for proliferation but are quiescent for cell division in the adult. The SCO cells also expressed GFAP, a marker for astrocytes or NSPCs, but not NeuN (for neurons). A few cells positive for Iba1 (microglia), Olig2 (for oligodendrocytes) and PDGFRα (oligodendrocyte progenitors) existed within or on the periphery of the SCO. These findings revealed that the SCO cells have a unique feature as secretory yet immature neuroepithelial cells in the adult mouse brain.

Background During development, Cajal-Retzius (CR) cells are the first generated and essential pioneering neurons that control neuronal migration and arealization in the mammalian cortex. CR cells are derived from specific regions within the telencephalon, that is, the pallial septum in the rostromedial cortex, the pallial-subpallial boundary, and the cortical hem (CH) in the caudomedial cortex. However, the molecular mechanism underlying the generation of CR cell subtypes in distinct regions of origin is poorly understood. Results We found that double-sex and mab-3 related transcription factor (Dmrt) genes, that is, Dmrta1 and Dmrt3, were expressed in the progenitor domains that produce CR cells. The number of CH-derived CR cells was severely decreased in Dmrt3 mutants, especially in Dmrta1 and Dmrt3 double mutants. The reduced production of the CR cells was consistent with the developmental impairment of the CH structures in the medial telencephalon from which the CR cells are produced. Conclusion Dmrta1 and Dmrt3 cooperatively regulate patterning of the CH structure and production of the CR cells from the CH during cortical development.

Advanced paternal age can have deleterious effects on various traits in the next generation. Here, we establish a paternal‐aging model in mice to understand the molecular mechanisms of transgenerational epigenetics. Whole‐genome target DNA methylome analyses of sperm from aged mice reveal more hypo‐methylated genomic regions enriched in REST/NRSF binding motifs. Gene set enrichment analyses also reveal the upregulation of REST/NRSF target genes in the forebrain of embryos from aged fathers. Offspring derived from young mice administrated with a DNA de‐methylation drug phenocopy the abnormal vocal communication of pups derived from aged fathers. In conclusion, hypo‐methylation of sperm DNA can be a key molecular feature modulating neurodevelopmental programs in offspring by causing fluctuations in the expression of REST/NRSF target genes., Paternal aging affects health and disease of the next generation, but the causative mechanisms are largely unknown. This study identifies hypo‐methylated sites enriched in REST/NRSF motifs in sperm DNA as epigenetic key features for inheritance.

Fragile X mental retardation protein (FMRP) is encoded byFMR1gene that is responsible for Fragile X Syndrome (FXS) showing intellectual disability and autism spectrum disorder. FMRP is an RNA binding protein highly expressed in the brain. Although several target genes for FMRP have been identified, limited studies have suggested the role of FMRP in corticogenesis. Here we performed RNA immunoprecipitation sequencing against the murine embryonic neocortex, and identified 124 genes as potential FMRP mRNA targets. We found 48 of these genes as overlapped with autism-related genes, which were categorized in four functional groups: “transcriptional regulation”, “regulation of actin cytoskeleton”, “ubiquitin-mediated proteolysis” and “calcium signaling pathway”. Four of these genes showed significant difference in expression in the cortical primordium ofFmr1-KO mice;Huwe1andKat6aincreased, whileKmt2candApcdecreased. Although the change in expression of these four genes was relatively small, these subtle changes due to dysregulated transcription could collectively contribute to impaired corticogenesis to cause phenotypes of FXS. Investigating the transcriptional control of FMRP on its mRNA targets may provide new insight to understand neurodevelopmental pathogenesis of FXS.

Advanced paternal age has deleterious effects on mental health of next generation. Using a mouse model, we have confirmed that offspring derived from aged fathers showed impairments in behavior and abnormalities in the brain structure and activity. Comprehensive target DNA methylome analyses revealed in aged sperm more hypo-methylated genomic regions, in which REST/NRSF binding motif was enriched. Gene set enrichment analyses also identified enrichment of “REST/NRSF target genes”, in addition to “Late-fetal genes” and autism spectrum disorder-related “SFARI genes”, in up-regulated genes of developing brains from aged father. Indeed, gene sets near hypo-methylated genomic regions with REST/NRSF binding motif were also enriched in up-regulated genes of developing brains. Taken altogether, DNA hypo-methylation due to paternal aging in sperm will induce leaky expression of REST/NRSF target genes in the developing brain, thereby causing neuronal abnormalities and subsequent behavioral alteration in offspring.

The evolution of unique organ structures is associated with changes in conserved developmental programs. However, characterizing the functional conservation and variation of homologous transcription factors (TFs) that dictate species-specific cellular dynamics has remained elusive. Here, we dissect shared and divergent functions of Pax6 during amniote brain development. Comparative functional analyses revealed that the neurogenic function of Pax6 is highly conserved in the developing mouse and chick pallium, whereas stage-specific binary functions of Pax6 in neurogenesis are unique to mouse neuronal progenitors, consistent with Pax6-dependent temporal regulation of Notch signaling. Furthermore, we identified that Pax6-dependent enhancer activity of Dbx1 is extensively conserved between mammals and chick, although Dbx1 expression in the developing pallium is highly divergent in these species. Our results suggest that spatiotemporal changes in Pax6-dependent regulatory programs contributed to species-specific neurogenic patterns in mammalian and avian lineages, which underlie the morphological divergence of the amniote pallial architectures., Highlighted Article: Pax6 promotes neuronal differentiation in the developing chick and mouse telencephalon via Notch inhibition, whereas its stage-specific function in RGC maintenance in the VZ is unique to mammalian neocortical progenitors.

Pax6 transcription factor is a key player in several aspects of brain development and function. Autism spectrum disorder (ASD) is a neurodevelopmental disorder in which several loci and/or genes have been suggested as causative candidate factors. Based on data obtained from meta-analyses of the transcriptome and ChIP analyses, we hypothesized that the neurodevelopmental gene PAX6 regulates and/or binds to a large number of genes (including many ASD-related ones) that modulate the fate of neural stem/progenitor cells and functions of neuronal cells, subsequently affecting animal behavior. Network analyses of PAX6/ASD-related molecules revealed significant clusters of molecular interactions involving regulation of cell-cell adhesion, ion transport, and transcriptional regulation. We discuss a novel function of Pax6 as a chromatin modulator that alters the chromatin status of ASD genes, thereby inducing diverse phenotypes of ASD and related neurodevelopmental diseases.

The anterior part of the embryonic telencephalon gives rise to several brain regions that are important for animal behavior, including the frontal cortex (FC) and the olfactory bulb. The FC plays an important role in decision-making behaviors, such as social and cognitive behavior, and the olfactory bulb is involved in olfaction. Here, we show the organizing activity of fibroblast growth factor 8 (Fgf8) in the regionalization of the anterior telencephalon, specifically the FC and the olfactory bulb. Misexpression of Fgf8 in the most anterior part of the mouse telencephalon at embryonic day 11.5 (E11.5) by ex utero electroporation resulted in a lateral shift of dorsal FC subdivision markers and a lateral expansion of the dorsomedial part of the FC, the future anterior cingulate and prelimbic cortex. Fgf8-transfected brains had lacked ventral FC, including the future orbital cortex, which was replaced by the expanded olfactory bulb. The olfactory region occupied a larger area of the FC when transfection efficiency of Fgf8 was higher. These results suggest that Fgf8 regulates the proportions of the FC and olfactory bulb in the anterior telencephalon and has a medializing effect on the formation of FC subdivisions.

Asymmetric cell division and cell cycle regulation are fundamental mechanisms of mammalian brain development and evolution. Cyclin D2, a positive regulator of G1 progression, shows a unique localization within radial glial (RG) cells (i.e., the neural progenitor in the developing neocortex). Cyclin D2 accumulates at the very basal tip of the RG cell (i.e., the basal endfoot) via a unique cis-regulatory sequence found in the 3' untranslated region (3'UTR) of its mRNA. During RG division, Cyclin D2 protein is asymmetrically distributed to two daughter cells following mitosis. The daughter cell that inherits Cyclin D2 mRNA maintains its self-renewal capability, while its sibling undergoes differentiation. A similar localization pattern of Cyclin D2 protein has been observed in the human fetal cortical primordium, suggesting a common mechanism of maintenance of neural progenitors that may be evolutionarily conserved across higher mammals such as primates. Here, we discuss our findings and the Cyclin D2 function in mammalian brain development and evolution.

Background Paternal age has deleterious effects on the transmission of phenotypes to offspring, including higher prevalence of major psychiatric and neurodevelopmental disorders. Methods Here, we examined transgenerational transmission of selected somatic and cognitive phenotypes in mice and explored a possible epigenetic mechanism. Results F1 offspring of aged fathers had lower body weight and showed impairment in pup's vocalization, sensorimotor gating and spatial learning. From comprehensive methylome analyses, we identified in aged sperm 16 hypermethylated and 96 hypomethylated genomic loci. Motif analysis identified 19 potential REST/NRSF-binding sites in hypomethylated regions, which was confirmed as 37 motifs with actual binding of REST in the ChIP-seq database using ES-derived neural stem cells. Since we also found reduction of thickness in the neocortex, especially in the deep layer, we analyzed expression of potential REST-target genes. Discussion All of the data consistently support the scenario that hypomethylation in sperm due to paternal age may eventually result in ectopic binding of REST repressor to its target genes, downregulating their expression during brain development, thereby inducing behavioral abnormalities in the offspring.

Pax6 is a transcription factor that pleiotropically regulates various developmental processes in the central nervous system. In a previous study, we revealed that Pax6 heterozygous mutant (rSey2/+) adult rats exhibit abnormalities in social interaction. However, the brain malformations underlying the behavioral abnormality are unknown. To elucidate the brain malformations in rSey2/+ rats, we morphometrically analyzed brains of rSey2/+ and wild type rats using small-animal magnetic resonance imaging (MRI). Sixty 10-week-old rats underwent brain MRI (29 rSey2/+ rats and 31 wild type rats). SPM8 software was used for image preprocessing and statistical image analysis. Normalized maps of the Jacobian determinant, a parameter for the expansion and/or contraction of brain regions, were obtained for each rat. rSey2/+ rats showed significant volume decreases in various brain regions including the neocortex, corpus callosum, olfactory structures, hippocampal formation, diencephalon, and midbrain compared to wild type rats. Among brain regions, the anterior commissure showed significant interaction between genotype and sex, indicating the effect of genotype difference on the anterior commissure volume was more robust in females than in males. The rSey2/+ rats exhibited decreased volume in various gray and white matter regions of the brain, which may contribute to manifestation of abnormal social behaviors.

Omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFAs) are essential nutrients. Although several studies have suggested that a balanced dietary n-6:n-3 ratio is essential for brain development, the underlying cellular and molecular mechanism is poorly understood. Here, we found that feeding pregnant mice an n-6 excess/n-3 deficient diet, which reflects modern human diets, impairsed neocortical neurogenesis in the offspring. This impaired neurodevelopment occurs through a precocious fate transition of neural stem cells from the neurogenic to gliogenic lineage. A comprehensive mediator lipidomics screen revealed key mediators, epoxy metabolites, which were confirmed functionally using a neurosphere assay. Importantly, although the offspring were raised on a well-balanced n-6:n-3 diet, they exhibited increased anxiety-related behavior in adulthood. These findings provide compelling evidence that excess maternal consumption of n-6 PUFAs combined with insufficient intake of n-3 PUFAs causes abnormal brain development that can have long-lasting effects on the offspring's mental state.

Mammalian whole embryo culture (WEC) is a widely used technique for examining pharmacological toxicity in developing mouse and rat embryos and for investigating the mechanisms of developmental processes. Immediately centrifuged (IC) rat serum is commonly used for WEC and is essential for the growth and development of cultured mouse and rat embryos ex vivo. For the culture of midgestation embryos (i.e., E8.0-12.5 for the mouse, and E10.0-14.5 for the rat), 100% rat serum is the best media for supporting the growth of the embryo ex vivo. To prepare rat serum suitable for WEC, the collected blood should be centrifuged immediately to separate the blood cells from the plasma fraction. After centrifugation, the fibrin clot forms in the upper layer; this clot should be squeezed gently using a pair of sterile forceps and subsequently centrifuged to completely separate the blood cells from the serum. In this video article, we demonstrate our standard protocol for the preparation of optimal IC rat serum, including blood collection from the abdominal aorta of male rats and extraction of the serum by centrifugation.

The transcription factor Pax6 balances cell proliferation and neuronal differentiation in the mammalian developing neocortex by regulating the expression of target genes. Using microarray analysis, we observed the down-regulation of Dmrta1 (doublesex and mab-3-related transcription factor-like family A1) in the telencephalon of Pax6 homozygous mutant rats (rSey(2) /rSey(2) ). Dmrta1 expression was restricted to the neural stem/progenitor cells of the dorsal telencephalon. Overexpression of Dmrta1 induced the expression of the proneural gene Neurogenin2 (Neurog2) and conversely repressed Ascl1 (Mash1), a proneural gene expressed in the ventral telencephalon. We found that another Dmrt family molecule, Dmrt3, induced Neurog2 expression in the dorsal telencephalon. Our novel findings suggest that dual regulation of proneural genes mediated by Pax6 and Dmrt family members is crucial for cortical neurogenesis.