Neural stem/precursor cells dynamically change their epigenetic landscape to differentially respond to BMP signaling for fate switching during brain development.

During neocortical development, tight regulation of neurogenesis-to-astrogenesis switching of neural precursor cells (NPCs) is critical to generate a balanced number of each neural cell type for proper brain functions. Accumulating evidence indicates that a complex array of epigenetic modifications and the availability of extracellular factors control the timing of neuronal and astrocytic differentiation. However, our understanding of NPC fate regulation is still far from complete. Bone morphogenetic proteins (BMPs) are renowned as cytokines that induce astrogenesis of gliogenic late-gestational NPCs. They also promote neurogenesis of mid-gestational NPCs, although the underlying mechanisms remain elusive. By performing multiple genome-wide analyses, we demonstrate that Smads, transcription factors that act downstream from BMP signaling, target dramatically different genomic regions in neurogenic and gliogenic NPCs. We found that histone H3K27 trimethylation and DNA methylation around Smad-binding sites change rapidly as gestation proceeds, strongly associated with the alteration of accessibility of Smads to their target binding sites. Furthermore, we identified two lineage-specific Smad-interacting partners-Sox11 for neurogenic and Sox8 for astrocytic differentiation-that further ensure Smad-regulated fate-specific gene induction. Our findings illuminate an exquisite regulation of NPC property change mediated by the interplay between cell-extrinsic cues and -intrinsic epigenetic programs during cortical development.

Reconstitution of the oocyte transcriptional network with transcription factors.

During female germline development, oocytes become a highly specialized cell type and form a maternal cytoplasmic store of crucial factors. Oocyte growth is triggered at the transition from primordial to primary follicle and is accompanied by dynamic changes in gene expression1, but the gene regulatory network that controls oocyte growth remains unknown. Here we identify a set of transcription factors that are sufficient to trigger oocyte growth. By investigation of the changes in gene expression and functional screening using an in vitro mouse oocyte development system, we identified eight transcription factors, each of which was essential for the transition from primordial to primary follicle. Notably, enforced expression of these transcription factors swiftly converted pluripotent stem cells into oocyte-like cells that were competent for fertilization and subsequent cleavage. These transcription-factor-induced oocyte-like cells were formed without specification of primordial germ cells, epigenetic reprogramming or meiosis, and demonstrate that oocyte growth and lineage-specific de novo DNA methylation are separable from the preceding epigenetic reprogramming in primordial germ cells. This study identifies a core set of transcription factors for orchestrating oocyte growth, and provides an alternative source of ooplasm, which is a unique material for reproductive biology and medicine.

The Derlin-1-Stat5b axis maintains homeostasis of adult hippocampal neurogenesis.

Adult neural stem cells (NSCs) in the hippocampal dentate gyrus continuously proliferate and generate new neurons throughout life. Although various functions of organelles are closely related to the regulation of adult neurogenesis, the role of endoplasmic reticulum (ER)-related molecules in this process remains largely unexplored. Here we show that Derlin-1, an ER-associated degradation component, spatiotemporally maintains adult hippocampal neurogenesis through a mechanism distinct from its established role as an ER quality controller. Derlin-1 deficiency in the mouse central nervous system leads to the ectopic localization of newborn neurons and impairs NSC transition from active to quiescent states, resulting in early depletion of hippocampal NSCs. As a result, Derlin-1-deficient mice exhibit phenotypes of increased seizure susceptibility and cognitive dysfunction. Reduced Stat5b expression is responsible for adult neurogenesis defects in Derlin-1-deficient NSCs. Inhibition of histone deacetylase activity effectively induces Stat5b expression and restores abnormal adult neurogenesis, resulting in improved seizure susceptibility and cognitive dysfunction in Derlin-1-deficient mice. Our findings indicate that the Derlin-1-Stat5b axis is indispensable for the homeostasis of adult hippocampal neurogenesis.

Direct neuronal conversion of microglia/macrophages reinstates neurological function after stroke.

Although generating new neurons in the ischemic injured brain would be an ideal approach to replenish the lost neurons for repairing the damage, the adult mammalian brain retains only limited neurogenic capability. Here, we show that direct conversion of microglia/macrophages into neurons in the brain has great potential as a therapeutic strategy for ischemic brain injury. After transient middle cerebral artery occlusion in adult mice, microglia/macrophages converge at the lesion core of the striatum, where neuronal loss is prominent. Targeted expression of a neurogenic transcription factor, NeuroD1, in microglia/macrophages in the injured striatum enables their conversion into induced neuronal cells that functionally integrate into the existing neuronal circuits. Furthermore, NeuroD1-mediated induced neuronal cell generation significantly improves neurological function in the mouse stroke model, and ablation of these cells abolishes the gained functional recovery. Our findings thus demonstrate that neuronal conversion contributes directly to functional recovery after stroke.

scRNA sequencing uncovers a TCF4-dependent transcription factor network regulating commissure development in mouse.

Transcription factor 4 (TCF4) is a crucial regulator of neurodevelopment and has been linked to the pathogenesis of autism, intellectual disability and schizophrenia. As a class I bHLH transcription factor (TF), it is assumed that TCF4 exerts its neurodevelopmental functions through dimerization with proneural class II bHLH TFs. Here, we aim to identify TF partners of TCF4 in the control of interhemispheric connectivity formation. Using a new bioinformatic strategy integrating TF expression levels and regulon activities from single cell RNA-sequencing data, we find evidence that TCF4 interacts with non-bHLH TFs and modulates their transcriptional activity in Satb2+ intercortical projection neurons. Notably, this network comprises regulators linked to the pathogenesis of neurodevelopmental disorders, e.g. FOXG1, SOX11 and BRG1. In support of the functional interaction of TCF4 with non-bHLH TFs, we find that TCF4 and SOX11 biochemically interact and cooperatively control commissure formation in vivo, and regulate the transcription of genes implicated in this process. In addition to identifying new candidate interactors of TCF4 in neurodevelopment, this study illustrates how scRNA-Seq data can be leveraged to predict TF networks in neurodevelopmental processes.

Lineage tracing identifies in vitro microglia-to-neuron conversion by NeuroD1 expression.

Neuronal regeneration to replenish lost neurons after injury is critical for brain repair. Microglia, brain-resident macrophages that have the propensity to accumulate at the site of injury, can be a potential source for replenishing lost neurons through fate conversion into neurons, induced by forced expression of neuronal lineage-specific transcription factors. However, it has not been strictly demonstrated that microglia, rather than central nervous system-associated macrophages, such as meningeal macrophages, convert into neurons. Here, we show that NeuroD1-transduced microglia can be successfully converted into neurons in vitro using lineage-mapping strategies. We also found that a chemical cocktail treatment further promoted NeuroD1-induced microglia-to-neuron conversion. NeuroD1 with loss-of-function mutation, on the other hand, failed to induce the neuronal conversion. Our results indicate that microglia are indeed reprogrammed into neurons by NeuroD1 with neurogenic transcriptional activity.

Inhibitory effects of extracts from Eucalyptus gunnii on α-synuclein amyloid fibrils.

Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Despite the numerous studies on the inhibition of amyloid formation, the prevention and treatment of a majority of amyloid-related disorders are still challenging. In this study, we investigated the effects of various plant extracts on amyloid formation of α-synuclein. We found that the extracts from Eucalyptus gunnii are able to inhibit amyloid formation, and to disaggregate preformed fibrils, in vitro. The extract itself did not lead to cell damage. In the extract, miquelianin, which is a glycosylated form of quercetin and has been detected in the plasma and the brain, was identified and assessed to have a moderate inhibitory activity, compared to the effects of ellagic acid and quercetin, which are strong inhibitors for amyloid formation. The properties of miquelianin provide insights into the mechanisms controlling the assembly of α-synuclein in the brain.

Early-life midazolam exposure persistently changes chromatin accessibility to impair adult hippocampal neurogenesis and cognition.

Linkage between early-life exposure to anesthesia and subsequent learning disabilities is of great concern to children and their families. Here we show that early-life exposure to midazolam (MDZ), a widely used drug in pediatric anesthesia, persistently alters chromatin accessibility and the expression of quiescence-associated genes in neural stem cells (NSCs) in the mouse hippocampus. The alterations led to a sustained restriction of NSC proliferation toward adulthood, resulting in a reduction of neurogenesis that was associated with the impairment of hippocampal-dependent memory functions. Moreover, we found that voluntary exercise restored hippocampal neurogenesis, normalized the MDZ-perturbed transcriptome, and ameliorated cognitive ability in MDZ-exposed mice. Our findings thus explain how pediatric anesthesia provokes long-term adverse effects on brain function and provide a possible therapeutic strategy for countering them.

CADM1 and CADM2 Trigger Neuropathogenic Measles Virus-Mediated Membrane Fusion by Acting in cis.

Measles virus (MeV), an enveloped RNA virus in the family Paramyxoviridae, is still an important cause of childhood morbidity and mortality worldwide. MeV usually causes acute febrile illness with skin rash, but in rare cases persists in the brain, causing a progressive neurological disorder, subacute sclerosing panencephalitis (SSPE). The disease is fatal, and no effective therapy is currently available. Although transsynaptic cell-to-cell transmission is thought to account for MeV propagation in the brain, neurons do not express the known receptors for MeV. Recent studies have shown that hyperfusogenic changes in the MeV fusion (F) protein play a key role in MeV propagation in the brain. However, how such mutant viruses spread in neurons remains unexplained. Here, we show that cell adhesion molecule 1 (CADM1; also known as IGSF4A, Necl-2, and SynCAM1) and CADM2 (also known as IGSF4D, Necl-3, SynCAM2) are host factors that enable MeV to cause membrane fusion in cells lacking the known receptors and to spread between neurons. During enveloped virus entry, a cellular receptor generally interacts in trans with the attachment protein on the envelope. However, CADM1 and CADM2 interact in cis with the MeV attachment protein on the same cell membrane, causing the fusion protein triggering and membrane fusion. Knockdown of CADM1 and CADM2 inhibits syncytium formation and virus transmission between neurons that are both mediated by hyperfusogenic F proteins. Thus, our results unravel the molecular mechanism (receptor-mimicking cis-acting fusion triggering) by which MeV spreads transsynaptically between neurons, thereby causing SSPE. IMPORTANCE Measles virus (MeV), an enveloped RNA virus, is the causative agent of measles, which is still an important cause of childhood morbidity and mortality worldwide. Persistent MeV infection in the brain causes a fatal progressive neurological disorder, subacute sclerosing panencephalitis (SSPE), several years after acute infection. However, how MeV spreads in neurons, which are mainly affected in SSPE, remains largely unknown. In this study, we demonstrate that cell adhesion molecule 1 (CADM1) and CADM2 are host factors enabling MeV spread between neurons. During enveloped virus entry, a cellular receptor generally interacts in trans with the attachment protein on the viral membrane (envelope). Remarkably, CADM1 and CADM2 interact in cis with the MeV attachment protein on the same membrane, triggering the fusion protein and causing membrane fusion, as viral receptors usually do in trans. Careful screening may lead to more examples of such "receptor-mimicking cis-acting fusion triggering" in other viruses.

Reconstitution in vitro of the entire cycle of the mouse female germ line.

The female germ line undergoes a unique sequence of differentiation processes that confers totipotency to the egg. The reconstitution of these events in vitro using pluripotent stem cells is a key achievement in reproductive biology and regenerative medicine. Here we report successful reconstitution in vitro of the entire process of oogenesis from mouse pluripotent stem cells. Fully potent mature oocytes were generated in culture from embryonic stem cells and from induced pluripotent stem cells derived from both embryonic fibroblasts and adult tail tip fibroblasts. Moreover, pluripotent stem cell lines were re-derived from the eggs that were generated in vitro, thereby reconstituting the full female germline cycle in a dish. This culture system will provide a platform for elucidating the molecular mechanisms underlying totipotency and the production of oocytes of other mammalian species in culture.

Transnasal transplantation of human induced pluripotent stem cell-derived microglia to the brain of immunocompetent mice.

Microglia are the resident immune cells of the brain, and play essential roles in neuronal development, homeostatic function, and neurodegenerative disease. Human microglia are relatively different from mouse microglia. However, most research on human microglia is performed in vitro, which does not accurately represent microglia characteristics under in vivo conditions. To elucidate the in vivo characteristics of human microglia, methods have been developed to generate and transplant induced pluripotent or embryonic stem cell-derived human microglia into neonatal or adult mouse brains. However, its widespread use remains limited by the technical difficulties of generating human microglia, as well as the need to use immune-deficient mice and conduct invasive surgeries. To address these issues, we developed a simplified method to generate induced pluripotent stem cell-derived human microglia and transplant them into the brain via a transnasal route in immunocompetent mice, in combination with a colony stimulating factor 1 receptor antagonist. We found that human microglia were able to migrate through the cribriform plate to different regions of the brain, proliferate, and become the dominant microglia in a region-specific manner by occupying the vacant niche when exogenous human cytokine is administered, for at least 60 days.

Enhanced processivity of Dnmt1 by monoubiquitinated histone H3.

DNA methylation controls gene expression, and once established, DNA methylation patterns are faithfully copied during DNA replication by the maintenance DNA methyltransferase Dnmt1. In vivo, Dnmt1 interacts with Uhrf1, which recognizes hemimethylated CpGs. Recently, we reported that Uhrf1-catalyzed K18- and K23-ubiquitinated histone H3 binds to the N-terminal region (the replication focus targeting sequence, RFTS) of Dnmt1 to stimulate its methyltransferase activity. However, it is not yet fully understood how ubiquitinated histone H3 stimulates Dnmt1 activity. Here, we show that monoubiquitinated histone H3 stimulates Dnmt1 activity toward DNA with multiple hemimethylated CpGs but not toward DNA with only a single hemimethylated CpG, suggesting an influence of ubiquitination on the processivity of Dnmt1. The Dnmt1 activity stimulated by monoubiquitinated histone H3 was additively enhanced by the Uhrf1 SRA domain, which also binds to RFTS. Thus, Dnmt1 activity is regulated by catalysis (ubiquitination)-dependent and -independent functions of Uhrf1.

Neuronal activation modulates enhancer activity of genes for excitatory synaptogenesis through de novo DNA methylation.

Post-mitotic neurons do exhibit DNA methylation changes, contrary to the longstanding belief that the epigenetic pattern in terminally differentiated cells is essentially unchanged. While the mechanism and physiological significance of DNA demethylation in neurons have been extensively elucidated, the occurrence of de novo DNA methylation and its impacts have been much less investigated. In the present study, we showed that neuronal activation induces de novo DNA methylation at enhancer regions, which can repress target genes in primary cultured hippocampal neurons. The functional significance of this de novo DNA methylation was underpinned by the demonstration that inhibition of DNA methyltransferase (DNMT) activity decreased neuronal activity-induced excitatory synaptogenesis. Overexpression of WW and C2 domain-containing 1 (Wwc1), a representative target gene of de novo DNA methylation, could phenocopy this DNMT inhibition-induced decrease in synaptogenesis. We found that both DNMT1 and DNMT3a were required for neuronal activity-induced de novo DNA methylation of the Wwc1 enhancer. Taken together, we concluded that neuronal activity-induced de novo DNA methylation that affects gene expression has an impact on neuronal physiology that is comparable to that of DNA demethylation. Since the different requirements of DNMTs for germ cell and embryonic development are known, our findings also have considerable implications for future studies on epigenomics in the field of reproductive biology.

Ectopic neurogenesis induced by prenatal antiepileptic drug exposure augments seizure susceptibility in adult mice.

Epilepsy is a neurological disorder often associated with seizure that affects ∼0.7% of pregnant women. During pregnancy, most epileptic patients are prescribed antiepileptic drugs (AEDs) such as valproic acid (VPA) to control seizure activity. Here, we show that prenatal exposure to VPA in mice increases seizure susceptibility in adult offspring through mislocalization of newborn neurons in the hippocampus. We confirmed that neurons newly generated from neural stem/progenitor cells (NS/PCs) are integrated into the granular cell layer in the adult hippocampus; however, prenatal VPA treatment altered the expression in NS/PCs of genes associated with cell migration, including CXC motif chemokine receptor 4 (Cxcr4), consequently increasing the ectopic localization of newborn neurons in the hilus. We also found that voluntary exercise in a running wheel suppressed this ectopic neurogenesis and countered the enhanced seizure susceptibility caused by prenatal VPA exposure, probably by normalizing the VPA-disrupted expression of multiple genes including Cxcr4 in adult NS/PCs. Replenishing Cxcr4 expression alone in NS/PCs was sufficient to overcome the aberrant migration of newborn neurons and increased seizure susceptibility in VPA-exposed mice. Thus, prenatal exposure to an AED, VPA, has a long-term effect on the behavior of NS/PCs in offspring, but this effect can be counteracted by a simple physical activity. Our findings offer a step to developing strategies for managing detrimental effects in offspring exposed to VPA in utero.

NFκB and TGFß contribute to the expression of PTPN3 in activated human lymphocytes.

We previously reported that protein tyrosine phosphatase non-receptor type 3 (PTPN3), which is upregulated in activated lymphocytes, acts as an immune checkpoint. However, the mechanism by which PTPN3 expression is enhanced in activated lymphocytes is unknown. In this study, we analyzed the mechanism of PTPN3 expression in activated lymphocytes with a view for developing a novel immune checkpoint inhibitor that suppresses PTPN3. Through the activation process, lymphocytes showed enhanced NFκB activation as well as increased PTPN3 expression. NFκB enhanced proliferation, migration, and cytotoxicity of lymphocytes. Furthermore, NFκB enhanced PTPN3 expression and tyrosine kinase activation. TGFß reduced PTPN3 expression and NFκB activation in the cancer microenvironment, and suppressed the biological activity of lymphocytes. The results of this study are expected to provide significant implications for improving existing immunotherapy and developing novel immunotherapy.

Canonical TGF-ß Signaling Negatively Regulates Neuronal Morphogenesis through TGIF/Smad Complex-Mediated CRMP2 Suppression.

Functional neuronal connectivity requires proper neuronal morphogenesis and its dysregulation causes neurodevelopmental diseases. Transforming growth factor-ß (TGF-ß) family cytokines play pivotal roles in development, but little is known about their contribution to morphological development of neurons. Here we show that the Smad-dependent canonical signaling of TGF-ß family cytokines negatively regulates neuronal morphogenesis during brain development. Mechanistically, activated Smads form a complex with transcriptional repressor TG-interacting factor (TGIF), and downregulate the expression of a neuronal polarity regulator, collapsin response mediator protein 2. We also demonstrate that TGF-ß family signaling inhibits neurite elongation of human induced pluripotent stem cell-derived neurons. Furthermore, the expression of TGF-ß receptor 1, Smad4, or TGIF, which have mutations found in patients with neurodevelopmental disorders, disrupted neuronal morphogenesis in both mouse (male and female) and human (female) neurons. Together, these findings suggest that the regulation of neuronal morphogenesis by an evolutionarily conserved function of TGF-ß signaling is involved in the pathogenesis of neurodevelopmental diseases.SIGNIFICANCE STATEMENT Canonical transforming growth factor-ß (TGF-ß) signaling plays a crucial role in multiple organ development, including brain, and mutations in components of the signaling pathway associated with several human developmental disorders. In this study, we found that Smads/TG-interacting factor-dependent canonical TGF-ß signaling regulates neuronal morphogenesis through the suppression of collapsin response mediator protein-2 (CRMP2) expression during brain development, and that function of this signaling is evolutionarily conserved in the mammalian brain. Mutations in canonical TGF-ß signaling factors identified in patients with neurodevelopmental disorders disrupt the morphological development of neurons. Thus, our results suggest that proper control of TGF-ß/Smads/CRMP2 signaling pathways is critical for the precise execution of neuronal morphogenesis, whose impairment eventually results in neurodevelopmental disorders.

Prior Treatment with Anti-High Mobility Group Box-1 Antibody Boosts Human Neural Stem Cell Transplantation-Mediated Functional Recovery After Spinal Cord Injury.

Together with residual host neurons, transplanted neural stem cell (NSC)-derived neurons play a critical role in reconstructing disrupted neural circuits after spinal cord injury (SCI). Since a large number of tracts are disrupted and the majority of host neurons die around the lesion site as the damage spreads, minimizing this spreading and preserving the lesion site are important for attaining further improvements in reconstruction. High mobility group box-1 (HMGB1) is a damage-associated molecular pattern protein that triggers sterile inflammation after tissue injury. In the ischemic and injured brain, neutralization of HMGB1 with a specific antibody reportedly stabilizes the blood-brain barrier, suppresses inflammatory cytokine expression, and improves functional recovery. Using a SCI model mouse, we here developed a combinatorial treatment for SCI: administering anti-HMGB1 antibody prior to transplantation of NSCs derived from human induced pluripotent stem cells (hiPSC-NSCs) yielded a dramatic improvement in locomotion recovery after SCI. Even anti-HMGB1 antibody treatment alone alleviated blood-spinal cord barrier disruption and edema formation, and increased the number of neurites from spared axons and the survival of host neurons, resulting in functional recovery. However, this recovery was greatly enhanced by the subsequent hiPSC-NSC transplantation, reaching an extent that has never before been reported. We also found that this improved recovery was directly associated with connections established between surviving host neurons and transplant-derived neurons. Taken together, our results highlight combinatorial treatment with anti-HMGB1 antibody and hiPSC-NSC transplantation as a promising novel therapy for SCI. Stem Cells 2018;36:737-750.

Early-life exposure to low levels of permethrin exerts impairments in learning and memory with the effects on neuronal and glial population in adult male mice.

Permethrin, a pyrethroid chemical, is widely used as a pesticide because of its rapid insecticidal activity. Although permethrin is considered to exert very low toxicity in mammals, the effects of early, low-level, chronic exposure on the adult central nervous system are unclear. In this study, we investigated the effects of low-level, chronic permethrin exposure in early life on the brain functions of adult mice, using environmentally relevant concentrations. We exposed mice to the acceptable daily intake level of permethrin (0.3 ppm) in drinking water during the prenatal and postnatal periods. We then examined the effects on the central nervous system in adult male offspring. In the permethrin group, we detected behavior that displayed incomplete adaptation to a novel environment, as well as an impairment in learning and memory. In addition, immunohistochemical analysis revealed an increase in doublecortin- (an immature neuron marker) positive cells in the hippocampal dentate gyrus in the permethrin exposure group compared with the control group. Additionally, in the permethrin exposure group there was a decrease in astrocyte number in the hilus of the dentate gyrus, and remaining astrocytes were often irregularly shaped. These results suggest that exposure to permethrin at low levels in early life affects the formation of the neural circuit base and behavior after maturation. Therefore, in the central nervous system of male mice, low-level, chronic permethrin exposure during the prenatal and postnatal periods has effects that were not expected based on the known effects of permethrin exposure in mature animals.

Neural stem cell therapy aiming at better functional recovery after spinal cord injury.

Injury to the spinal cord causes transection of axon fibers and neural cell death, resulting in disruption of the neural network and severe functional loss. Reconstruction of the damaged neural circuits was once considered to be hopeless as the adult mammalian central nervous system has very poor ability to regenerate. For this reason, there is currently no effective therapeutic treatment for spinal cord injury (SCI). However, with recent developments in stem cell research and cell culture technology, regenerative therapy using neural stem cell (NSC) transplantation has rapidly been developed, and this therapeutic strategy makes it possible to rebuild the destroyed neural circuits. In this review, we discuss the recent breakthroughs in NSC transplantation therapy for SCI. Developmental Dynamics 247:75-84, 2018. © 2017 Wiley Periodicals, Inc.

HMGB2 expression is associated with transition from a quiescent to an activated state of adult neural stem cells.

BACKGROUND: Although quiescent neural stem cells (NSCs) in the adult hippocampus proliferate in response to neurogenic stimuli and subsequently give rise to new neurons continuously throughout life, misregulation of NSCs in pathological conditions, including aging, leads to the impairment of learning and memory. High mobility group B family 1 (HMGB1) and HMGB2, HMG family proteins that function as transcriptional activators through the modulation of chromatin structure, have been assumed to play some role in the regulation of adult NSCs; however, their precise functions and even expression patterns in the adult hippocampus remain elusive. RESULTS: Here we show that expression of HMGB2 but not HMGB1 is restricted to the subset of NSCs and their progenitors. Furthermore, running, a well-known positive neurogenic stimulus, increased the proliferation of HMGB2-expressing cells, whereas aging was accompanied by a marked decrease in these cells. Intriguingly, HMGB2-expressing quiescent NSCs, which were shifted toward the proliferative state, were decreased as aging progressed. CONCLUSIONS: HMGB2 expression is strongly associated with transition from the quiescent to the proliferative state of NSCs, supporting the possibility that HMGB2 is involved in the regulation of adult neurogenesis and can be used as a novel marker to identify NSCs primed for activation in the adult hippocampus. Developmental Dynamics 247:229-238, 2018. © 2017 Wiley Periodicals, Inc.