Postnatal expression of Doublecortin (Dcx) in the developing cerebellar cortex of mouse

Cytomegalovirus infection lengthens the cell cycle of granule cell precursors during postnatal cerebellar development

Human cytomegalovirus (HCMV) infection in infants infected in utero can lead to a variety of neurodevelopmental disorders. However, mechanisms underlying altered neurodevelopment in infected infants remain poorly understood. We have previously described a murine model of congenital HCMV infection in which murine CMV (MCMV) spreads hematogenously and establishes a focal infection in all regions of the brain of newborn mice, including the cerebellum. Infection resulted in disruption of cerebellar cortical development characterized by reduced cerebellar size and foliation. This disruption was associated with altered cell cycle progression of the granule cell precursors (GCPs), which are the progenitors that give rise to granule cells (GCs), the most abundant neurons in the cerebellum. In the current study, we have demonstrated that MCMV infection leads to prolonged GCP cell cycle, premature exit from the cell cycle, and reduced numbers of GCs resulting in cerebellar hypoplasia. Treatment with TNF-α neutralizing antibody partially normalized the cell cycle alterations of GCPs and altered cerebellar morphogenesis induced by MCMV infection. Collectively, our results argue that virus-induced inflammation altered the cell cycle of GCPs resulting in a reduced numbers of GCs and cerebellar cortical hypoplasia, thus providing a potential mechanism for altered neurodevelopment in fetuses infected with HCMV.

Temporal analysis of enhancers during mouse cerebellar development reveals dynamic and novel regulatory functions

We have identified active enhancers in the mouse cerebellum at embryonic and postnatal stages which provides a view of novel enhancers active during cerebellar development. The majority of cerebellar enhancers have dynamic activity between embryonic and postnatal development. Cerebellar enhancers were enriched for neural transcription factor binding sites with temporally specific expression. Putative gene targets displayed spatially restricted expression patterns, indicating cell-type specific expression regulation. Functional analysis of target genes indicated that enhancers regulate processes spanning several developmental epochs such as specification, differentiation and maturation. We use these analyses to discover one novel regulator and one novel marker of cerebellar development: Bhlhe22 and Pax3, respectively. We identified an enrichment of de novo mutations and variants associated with autism spectrum disorder in cerebellar enhancers. Furthermore, by comparing our data with relevant brain development ENCODE histone profiles and cerebellar single-cell datasets we have been able to generalize and expand on the presented analyses, respectively. We have made the results of our analyses available online in the Developing Mouse Cerebellum Enhancer Atlas (https://goldowitzlab.shinyapps.io/developing_mouse_cerebellum_enhancer_atlas/), where our dataset can be efficiently queried, curated and exported by the scientific community to facilitate future research efforts. Our study provides a valuable resource for studying the dynamics of gene expression regulation by enhancers in the developing cerebellum and delivers a rich dataset of novel gene-enhancer associations providing a basis for future in-depth studies in the cerebellum.

Early postnatal development of the visual cortex in mice with retinal degeneration

This study characterizes the early postnatal development of the visual neocortex in C3H/HeNRj mice. These mice are homozygous for the Pde6b^rd1 mutation, which causes retinal degeneration starting from postnatal day 7 (P7). To monitor the development of the visual cortex between P3 and P28 we used eight antigens known to be expressed at different developmental stages (Nestin, tau3, β3- Tubulin, Calbindin, Doublecortin, MAP2, Parvalbumin and NeuN). Using semiquantitative analysis we traced the expression and localization of different developmental markers throughout the layers of the visual cortex. Cortical tissue sections corresponding to the first postnatal week (P3-P6) stained positively for Nestin, tau3, β3-Tubulin and Calbindin. These proteins are known to be involved in the migration of neural progenitor cells (NPCs) within the cortical plate. At the time of eye-opening (P14), Doublecortin, MAP2 and NeuN, markers for developing and maturing neurons involved in NPC differentiation are present. Between P9 and P21 Nestin and Calbindin disappear while NeuN and Parvalbumin expression increases in the course of visual neocortex development. The findings of this study provide a snapshot of the dynamic changes in cortex formation during early postnatal development. So far, it is the first investigation on the postnatal development of the mouse visual cortex. Our results indicate that in C3H/HeNRj mice retinal degeneration during these early stages may not influence the maturation of the visual cortex. Until P28 in this mouse strain, the development of the visual neocortex is in accordance with data from other mice (C57BL/6) without retinal degeneration. Whether in older individuals of the C3H/HeNRj strain the visual neocortex will show signs of functional impairment has to be shown by future work.

Cerebellar networks and neuropathology of cerebellar developmental disorders

The cerebellar system is a series of axonal projections and synaptic circuits as networks, similar to those of the limbic system and those subserving the propagation and spread of seizures. Three principal cerebellar networks are identified and cerebellar disease often affects components of the networks other than just the cerebellar cortex. Contemporary developmental neuropathology of the cerebellum is best considered in the context of alterations of developmental processes: embryonic segmentation and genetic gradients along the three axes of the neural tube, individual neuronal and glial cell differentiation, migration, synaptogenesis, and myelination. Precisely timed developmental processes may be delayed or precocious rhombencephalosynapsis and pontocerebellar hypoplasia exemplify opposite gradients in the horizontal axis. Chiari II malformation may be reconsidered as a disorder of segmentation rather than simply due to mechanical forces upon normally developing hindbrain structures. Cellular nodules in the roof of the fourth ventricle are heterotopia of histologically differentiated but architecturally disoriented and disorganized neurons and glial cells; they often are less mature immunocytochemically than similar cells in adjacent normal folia. Cell rests are nodules of undifferentiated neuroepithelial cells. Both are frequent in human fetuses and neonates. Axonal projections from heterotopia to adjacent cerebellar folia or nuclei are few or absent, hence these nodules are clinically silent despite neuronal differentiation.

Limited effects of preterm birth and the first enteral nutrition on cerebellum morphology and gene expression in piglets

Preterm pigs show many signs of immaturity that are characteristic of preterm infants. In preterm infants, the cerebellum grows particularly rapid and hypoplasia and cellular lesions are associated with motor dysfunction and cognitive deficits. We hypothesized that functional brain delays observed in preterm pigs would be paralleled by both structural and molecular differences in the cerebellum relative to term born piglets. Cerebella were collected from term (n = 56) and preterm (90% gestation, n = 112) pigs at 0, 5, and 26 days after birth for stereological volume estimations, large‐scale qPCR gene expression analyses (selected neurodevelopmental genes) and western blot protein expression analysis (Sonic Hedgehog pathway). Memory and learning was tested using a T‐maze, documenting that preterm pigs showed delayed learning. Preterm pigs also showed reduced volume of both white and gray matter at all three ages but the proportion of white matter increased postnatally, relative to term pigs. Early initiation of enteral nutrition had limited structural or molecular effects. The Sonic Hedgehog pathway was unaffected by preterm birth. Few differences in expression of the selected genes were found, except consistently higher mRNA levels of Midkine, p75, and Neurotrophic factor 3 in the preterm cerebellum postnatally, probably reflecting an adaptive response to preterm birth. Pig cerebellar development appears more affected by postconceptional age than by environmental factors at birth or postnatally. Compensatory mechanisms following preterm birth may include faster white matter growth and increased expression of selected genes for neurotrophic factors and regulation of angiogenesis. While the pig cerebellum is immature in 90% gestation preterm pigs, it appears relatively mature and resilient toward environmental factors.

Analysis of hedgehog signaling in cerebellar granule cell precursors in a conditional Nsdhl allele demonstrates an essential role for cholesterol in postnatal CNS development

NSDHL is a 3β-hydroxysterol dehydrogenase that is involved in the removal of two C-4 methyl groups in one of the later steps of cholesterol biosynthesis. Mutations in the gene encoding the enzyme are responsible for the X-linked, male lethal mouse mutations bare patches and striated, as well as most cases of human CHILD syndrome. Rare, hypomorphic NSDHL mutations are also associated with X-linked intellectual disability in males with CK syndrome. Since hemizygous male mice with Nsdhl mutations die by midgestation, we generated a conditional targeted Nsdhl mutation (Nsdhl(tm1.1Hrm)) to investigate the essential role of cholesterol in the early postnatal CNS. Ablation of Nsdhl in radial glia using GFAP-cre resulted in live-born, normal appearing affected male pups. However, the pups develop overt ataxia by postnatal day 8-10 and die shortly thereafter. Histological abnormalities include progressive loss of cortical and hippocampal neurons, as well as deficits in the proliferation and migration of cerebellar granule precursors and subsequent massive apoptosis of the cerebellar cortex. We replicated the granule cell precursor proliferation defect in vitro and demonstrate that it results from defective signaling by SHH. Furthermore, this defect is almost completely rescued by supplementation of the culture media with exogenous cholesterol, while methylsterol accumulation above the enzymatic block appears to be associated with increased cell death. These data support the absolute requirement for cholesterol synthesis in situ once the blood-brain-barrier forms and cholesterol transport to the fetus is abolished. They further emphasize the complex ramifications of cholesterogenic enzyme deficiency on cellular metabolism.

Cellular and axonal diversity in molecular layer heterotopia of the rat cerebellar vermis

Molecular layer heterotopia of the cerebellar primary fissure are a characteristic of many rat strains and are hypothesized to result from defect of granule cells exiting the external granule cell layer during cerebellar development. However, the cellular and axonal constituents of these malformations remain poorly understood. In the present report, we use histochemistry and immunocytochemistry to identify neuronal, glial, and axonal classes in molecular layer heterotopia. In particular, we identify parvalbumin-expressing molecular layer interneurons in heterotopia as well as three glial cell types including Bergmann glia, Olig2-expressing oligodendrocytes, and Iba1-expressing microglia. In addition, we document the presence of myelinated, serotonergic, catecholaminergic, and cholinergic axons in heterotopia indicating possible spinal and brainstem afferent projections to heterotopic cells. These findings are relevant toward understanding the mechanisms of normal and abnormal cerebellar development.

Neuronal migration defect of the developing cerebellar vermis in substrains of C57BL/6 mice: cytoarchitecture and prevalence of molecular layer heterotopia

Abnormal development of the cerebellum is often associated with disorders of movement, postural control, and motor learning. Rodent models are widely used to study normal and abnormal cerebellar development and have revealed the roles of many important genetic and environmental factors. In the present report we describe the prevalence and cytoarchitecture of molecular-layer heterotopia, a malformation of neuronal migration, in the cerebellar vermis of C57BL/6 mice and closely-related strains. In particular, we found a diverse number of cell-types affected by these malformations including Purkinje cells, granule cells, inhibitory interneurons (GABAergic and glycinergic), and glia. Heterotopia were not observed in a sample of wild-derived mice, outbred mice, or inbred mice not closely related to C57BL/6 mice. These data are relevant to the use of C57BL/6 mice as models in the study of brain and behavior relationships and provide greater understanding of human cerebellar dysplasia.

Perinatal iodine deficiency and hypothyroidism increase cell apoptosis and alter doublecortin and reelin protein expressions in rat cerebellum

BACKGROUND AND AIMS

Adequate thyroid hormone is critical for cerebellar development. Developmental hypothyroidism induced by iodine deficiency during the perinatal period results in permanent impairments of cerebellar development with an unclear mechanism. In the present study we investigated effects of perinatal iodine deficiency and hypothyroidism on cerebellar cell apoptosis, doublecortin (Dcx) and reelin. Apoptosis is an essential part of neural development. Dcx and reelin are two important molecules involved in neuronal migration, structure, and development in cerebellum.

METHODS

Two developmental rat models were created by administering dam rats with either iodine-deficient diet or propylthiouracil (PTU, 5 ppm or 15 ppm)-added drinking water from gestational day (GD) 6 until postnatal day (PND) 28. TUNEL assay and protein levels of Dcx and reelin in cerebella were assessed on PND14, 21 and 28.

RESULTS

Apoptotic cells were increased in the iodine-deficient and PTU-treated rats. Dcx protein levels in the cerebella of iodine-deficient and PTU-treated rats were significantly downregulated on PND14. Interestingly, iodine deficiency and PTU treatment upregulated the levels of Dcx protein on PND21 and 28. Reelin expressions in iodine-deficient and PTU-treated rats were significantly decreased on PND14 and 21. On PND28, reelin expressions of three treated groups were still lower than control group, although without significant difference.

CONCLUSIONS

These findings may implicate alterations in cell apoptosis and levels of Dcx and reelin in the impairments of cerebellar development induced by developmental iodine deficiency and hypothyroidism.

Systemic hypoxia differentially affects neurogenesis during early mouse brain maturation

BACKGROUND

Cerebral tissue oxygen level modifies crucial processes of neurogenesis, glial and neuronal development during physiological and hypoxic conditions. Whether hypoxia-sensitive factors such as doublecortin (DCX) and hypoxia-inducible transcription factor (HIF)-regulated CXCR4 and SDF-1 modify and activate adaptation to hypoxia in developing brain is not well understood. Present study investigated maturational regulation of oxygen-sensitive developmental genes and proteins in developing mouse brain in relation to the degree of hypoxia.

METHODS

Physiological expression of HIF-1, CXCR4, SDF-1 and DCX were analyzed in the brain of C57/BL6 mice (P0-P60). In addition, mice (P0, P7) were exposed to normoxia, acute (8% O(2), 6 h) or chronic hypoxia (10% O(2), 7 d) followed by reoxygenation. Gene expression was analyzed by quantitative PCR, proteins were quantified by Western blot analysis and immunohistochemistry.

RESULTS

Cerebral HIF-1α protein, CXCR4 and DCX mRNA levels showed maturational stage-related peak levels at P0/P1, whereas SDF-1 mRNA levels were highest at P17. CXCR4 and SDF-1 mRNA levels were not altered in response to hypoxia. Whereas DCX mRNA levels significantly increased during acute hypoxia, down-regulation of DCX transcripts was found in response to chronic hypoxia compared to controls, and these changes were related to specifically vulnerable brain regions.

CONCLUSIONS

Maturational stage-related dynamic changes of HIF-1α, CXCR4, SDF-1 and DCX may reflect involvement of hypoxia-regulated systems in important developmental regulatory processes of the developing brain. Extending the knowledge of differential effects of hypoxia on neurogenesis and dynamic regulatory networks present data provide a basis for future research on gestational age-specific neuroprotective options.

Postnatal changes in the distribution and density of neuronal nuclei and doublecortin antigens in domestic chicks (Gallus domesticus)

To understand better the rate of neurogenesis and the distribution of new neurons in posthatch domestic chicks, we describe and compare the expression of the neuronal nuclei protein (NeuN, a.k.a. Fox-3) and doublecortin antigens in the whole brain of chicks 2 days, 8 days, and 14 weeks posthatch. In the forebrain ventricular and paraventricular zones, the density of bromodeoxyuridine-, NeuN-, and doublecortin-labeled cells was compared between chicks 24 hours and 7 days after an injection of bromodeoxyuridine (2 and 8 days posthatch, respectively). The distribution of NeuN-labeled neurons was similar to Nissl-stained tissue, with the exception of some areas where neurons did not express NeuN: cerebellar Purkinje cells and olfactory bulb mitral cells. The ventral tegmental area of 2-day-old chicks was also faintly labeled. The distribution of doublecortin was similar at all timepoints, with doublecortin-labeled profiles located throughout all forebrain areas as well as in the cerebellar granule cell layer. However, doublecortin labeling was not detectable in any midbrain or brainstem areas. Our data indicate that a significant number of new neurons is still formed in the telencephalon of posthatch domestic chicks, whereas subtelencephalic areas (except for the cerebellum) finish their neuronal expansion before hatching. Most newly formed cells in chicks leave the paraventricular zone after hatching, but a pool of neurons stays in the vicinity of the ventricular zone and matures in situ within 7 days. Proliferating cells often migrate laterally along forebrain laminae into still-developing brain areas.

Time course of postnatal distribution of doublecortin immunoreactive developing/maturing neurons in the somatosensory cortex and hippocampal CA1 region of C57BL/6 mice

In this study, we observed neuroblast differentiation in the somatosensory cortex (SSC) and hippocampal CA1 region (CA1), which is vulnerable to oxidative stress, of the mouse at various early postnatal days (P) 1, 7, 14, and 21 using doublecortin (DCX, a marker for neuroblasts). Cresyl violet and NeuN (Neuronal Nuclei) staining showed development of layers as well as neurons in the SSC and CA1. At P1, DCX-positive neuroblasts expressed strong DCX immunoreactivity in both the SSC and CA1. Thereafter, DCX immunoreactivity was decreased with time. At P7, many DCX-immunoreactive neuroblasts were well detected in the SSC and CA1. At P14, some DCX-positive neuroblasts were found in the SSC and CA1: The immunoreactivity was weak. At P21, DCX immunoreactivity was hardly found in cells in the SSC and CA1. These results suggest that DCX-positive neuroblasts were significantly decreased in the mouse SSC and CA1 from P14.

A powerful transgenic tool for fate mapping and functional analysis of newly generated neurons

BACKGROUND

Lack of appropriate tools and techniques to study fate and functional integration of newly generated neurons has so far hindered understanding of neurogenesis' relevance under physiological and pathological conditions. Current analyses are either dependent on mitotic labeling, for example BrdU-incorporation or retroviral infection, or on the detection of transient immature neuronal markers. Here, we report a transgenic mouse model (DCX-CreERT2) for time-resolved fate analysis of newly generated neurons. This model is based on the expression of a tamoxifen-inducible Cre recombinase under the control of a doublecortin (DCX) promoter, which is specific for immature neuronal cells in the CNS.

RESULTS

In the DCX-CreERT2 transgenic mice, expression of CreERT2 was restricted to DCX+ cells. In the CNS of transgenic embryos and adult DCX-CreERT2 mice, tamoxifen administration caused the transient translocation of CreERT2 to the nucleus, allowing for the recombination of loxP-flanked sequences. In our system, tamoxifen administration at E14.5 resulted in reporter gene activation throughout the developing CNS of transgenic embryos. In the adult CNS, neurogenic regions were the primary sites of tamoxifen-induced reporter gene activation. In addition, reporter expression could also be detected outside of neurogenic regions in cells physiologically expressing DCX (e.g. piriform cortex, corpus callosum, hypothalamus). Four weeks after recombination, the vast majority of reporter-expressing cells were found to co-express NeuN, revealing the neuronal fate of DCX+ cells upon maturation.

CONCLUSIONS

This first validation demonstrates that our new DCX-CreERT2 transgenic mouse model constitutes a powerful tool to investigate neurogenesis, migration and their long-term fate of neuronal precursors. Moreover, it allows for a targeted activation or deletion of specific genes in neuronal precursors and will thereby contribute to unravel the molecular mechanisms controlling neurogenesis.

Radial glial cells and the lamination of the cerebellar cortex

Radial glial cells are stem cells that play an important role in neuronal migration and proliferation in the developing brain. However, how radial glial cells contribute to the lamination of the cerebellar cortex is not well understood. We therefore used immunohistochemistry and BrdU labeling to follow radial glial cell differentiation, cell migration and cerebellar cortex development in mice from embryonic day 8 to postnatal day 180. We report that radial glial cells represent the stem cell population of the neuroepithelium of the neural tube, and act as progenitors for both neurons and neuroglia. In addition, radial glial cells not only give rise to the principal cells of the cerebellar cortex, the Purkinje and granule cells, but they also provide a scaffold for the migration of these cells. We conclude that radial glial cells play a pivotal role in establishing the laminar structure of the cerebellar cortex.