Cux2 activity defines a subpopulation of perinatal neurogenic progenitors in the hippocampus

Cerebellar granule cell migration and folia development require Mllt11/Af1q/Tcf7c

The organization of neurons into distinct layers, known as lamination, is a common feature of the nervous system. This process, which arises from the direct coupling of neurogenesis and neuronal migration, plays a crucial role in the development of the cerebellum, a structure exhibiting a distinct folding cytoarchitecture with cells arranged in discrete layers. Disruptions to neuronal migration can lead to various neurodevelopmental disorders, highlighting the significance of understanding the molecular regulation of lamination. We report a role Mllt11/Af1q/Tcf7c (myeloid/lymphoid or mixed-lineage leukemia; translocated to chromosome 11/All1 fused gene from chromosome 1q, also known as Mllt11 transcriptional cofactor 7; henceforth referred to Mllt11) in the migration of cerebellar granule cells (GCs). We now show that Mllt11 plays a role in both the tangential and radial migration of GCs. Loss of Mllt11 led to an accumulation of GC precursors in the rhombic lip region and a reduction in the number of GCs successfully populating developing folia. Consequently, this results in smaller folia and an overall reduction in cerebellar size. Furthermore, analysis of the anchoring centers reveals disruptions in the perinatal folia cytoarchitecture, including alterations in the Bergmann glia fiber orientation and reduced infolding of the Purkinje cell plate. Lastly, we demonstrate that Mllt11 interacts with non-muscle myosin IIB (NMIIB) and Mllt11 loss-reduced NMIIB expression. We propose that the dysregulation of NMIIB underlies altered GC migratory behavior. Taken together, the findings reported herein demonstrate a role for Mllt11 in regulating neuronal migration within the developing cerebellum, which is necessary for its proper neuroanatomical organization.

The challenges in the interpretation of genetic variants detected by genomics techniques in patients with congenital anomalies

BACKGROUND

Despite the efforts that have been made to standardize the interpretation of variants, in some cases, their pathogenicity remains vague and confusing, and sometimes their interpretation does not help clinicians to establish clinical correlation using genetic test results. This study aims to shed more lights on these challenging variants.

METHODS

In a clinical setting, the variants found from 81 array CGH and 79 whole exome sequencing (WES) in patients with congenital anomalies were interpreted based on American College of Medical Genetics and Genomics guidelines.

RESULTS

In this study, the interpretation of the disease-causing variants and the variants with uncertain clinical significance detected by WES was far more challenging than the variants detected by array CGH. The presence of unreported clinical symptoms, incomplete penetrance, variable expressivity, parents' reluctance to analyze segregation in the family, and the limitations of prenatal tests, were among the challenging factors in the interpretation of variants in this study.

CONCLUSION

A careful study of the pedigree and disease mode of inheritance, as well as a careful clinical examination of the carrier parents in diseases with autosomal dominant inheritance, are among the primary strategies for determining the clinical significance of the variants. Continued efforts to mitigate these challenges are needed to improve the interpretation of variants.

Retinal neuroblast migration and ganglion cell layer organization require the cytoskeletal-interacting protein Mllt11

BACKGROUND

The vertebrate retina is an organized laminar structure comprised of distinct cell types populating three nuclear layers. During development, each retinal cell type follows a stereotypical temporal order of genesis, differentiation, and migration, giving rise to its stratified organization. Once born, the precise positioning of cells along the apico-basal (radial) axis of the retina is critical for subsequent connections to form, relying on highly orchestrated migratory processes. While these processes are critical for visual function to arise, the regulators of cellular migration and retinal lamination remain largely unexplored.

RESULTS

We report a role for a microtubule-interacting protein, Mllt11 (myeloid/lymphoid or mixed-lineage leukemia; translocated to chromosome 11/All1 fused gene from chromosome 1q) in mammalian retinal cell migration during retinogenesis. We show that Mllt11 loss-of-function in mouse retinal neuroblasts affected the migration of ganglion and amacrine cells into the ganglion cell layer and led to their aberrant accumulation in the inner nuclear and plexiform layers.

CONCLUSIONS

We demonstrate a role for Mllt11 in neuroblast migration and formation of the ganglion cell layer of the retina.

A single-nucleus transcriptomic atlas of the dog hippocampus reveals the potential relationship between specific cell types and domestication

The process of domestication has led to dramatic differences in behavioral traits between domestic dogs and gray wolves. Whole-genome research found that a class of putative positively selected genes were related to various aspects of learning and memory, such as long-term potentiation and long-term depression. In this study, we constructed a single-nucleus transcriptomic atlas of the dog hippocampus to illustrate its cell types, cell lineage and molecular features. Using the transcriptomes of 105 057 nuclei from the hippocampus of a Beagle dog, we identified 26 cell clusters and a putative trajectory of oligodendrocyte development. Comparative analysis revealed a significant convergence between dog differentially expressed genes (DEGs) and putative positively selected genes (PSGs). Forty putative PSGs were DEGs in glutamatergic neurons, especially in Cluster 14, which is related to the regulation of nervous system development. In summary, this study provides a blueprint to understand the cellular mechanism of dog domestication.

Base excision repair accessory factors in senescence avoidance and resistance to treatments

Cancer cells, in which the RAS and PI3K pathways are activated, produce high levels of reactive oxygen species (ROS), which cause oxidative DNA damage and ultimately cellular senescence. This process has been documented in tissue culture, mouse models, and human pre-cancerous lesions. In this context, cellular senescence functions as a tumour suppressor mechanism. Some rare cancer cells, however, manage to adapt to avoid senescence and continue to proliferate. One well-documented mode of adaptation involves increased production of antioxidants often associated with inactivation of the KEAP1 tumour suppressor gene and the resulting upregulation of the NRF2 transcription factor. In this review, we detail an alternative mode of adaptation to oxidative DNA damage induced by ROS: the increased activity of the base excision repair (BER) pathway, achieved through the enhanced expression of BER enzymes and DNA repair accessory factors. These proteins, exemplified here by the CUT domain proteins CUX1, CUX2, and SATB1, stimulate the activity of BER enzymes. The ensued accelerated repair of oxidative DNA damage enables cancer cells to avoid senescence despite high ROS levels. As a by-product of this adaptation, these cancer cells exhibit increased resistance to genotoxic treatments including ionizing radiation, temozolomide, and cisplatin. Moreover, considering the intrinsic error rate associated with DNA repair and translesion synthesis, the elevated number of oxidative DNA lesions caused by high ROS leads to the accumulation of mutations in the cancer cell population, thereby contributing to tumour heterogeneity and eventually to the acquisition of resistance, a major obstacle to clinical treatment.

Mllt11 Regulates Migration and Neurite Outgrowth of Cortical Projection Neurons during Development

The formation of connections within the mammalian neocortex is highly regulated by both extracellular guidance mechanisms and intrinsic gene expression programs. There are two types of cortical projection neurons (CPNs): those that project locally and interhemispherically and those that project to subcerebral structures such as the thalamus, hindbrain, and spinal cord. The regulation of cortical projection morphologies is not yet fully understood at the molecular level. Here, we report a role for Mllt11 (Myeloid/lymphoid or mixed-lineage leukemia; translocated to chromosome 11/All1 Fused Gene From Chromosome 1q) in the migration and neurite outgrowth of callosal projection neurons during mouse brain formation. We show that Mllt11 expression is exclusive to developing neurons and is enriched in the developing cortical plate (CP) during the formation of the superficial cortical layers. In cultured primary cortical neurons, Mllt11 is detected in varicosities and growth cones as well as the soma. Using conditional loss-of-function and gain-of-function analysis we show that Mllt11 is required for neuritogenesis and proper migration of upper layer CPNs. Loss of Mllt11 in the superficial cortex of male and female neonates leads to a severe reduction in fibers crossing the corpus callosum (CC), a progressive loss in the maintenance of upper layer projection neuron gene expression, and reduced complexity of dendritic arborization. Proteomic analysis revealed that Mllt11 associates with stabilized microtubules, and Mllt11 loss affected microtubule staining in callosal axons. Taken together, our findings support a role for Mllt11 in promoting the formation of mature upper-layer neuron morphologies and connectivity in the cerebral cortex.SIGNIFICANCE STATEMENT The regulation of cortical projection neuron (CPN) morphologies is an area of active investigation since the time of Cajal. Yet the molecular mechanisms of how the complex dendritic and axonal morphologies of projection neurons are formed remains incompletely understood. Although conditional mutagenesis analysis in the mouse, coupled with overexpression assays in the developing fetal brain, we show that a novel protein called Mllt11 is sufficient and necessary to regulate the dendritic and axonal characteristics of callosal projection neurons in the developing mammalian neocortex. Furthermore, we show that Mllt11 interacts with microtubules, likely accounting for its role in neuritogenesis.

Development of the mammalian cortical hem and its derivatives: the choroid plexus, Cajal-Retzius cells and hippocampus

The dorsal medial region of the developing mammalian telencephalon plays a central role in the patterning of the adjacent brain regions. This review describes the development of this specialized region of the vertebrate brain, called the cortical hem, and the formation of the various cells and structures it gives rise to, including the choroid plexus, Cajal–Retzius cells and the hippocampus. We highlight the ontogenic processes that create these different forebrain derivatives from their shared embryonic origin and discuss the key signalling pathways and molecules that influence the patterning of the cortical hem. These include BMP, Wnt, FGF and Shh signalling pathways acting with Homeobox factors to carve the medial telencephalon into district progenitor regions, which in turn give rise to the choroid plexus, dentate gyrus and hippocampus. We then link the formation of the lateral ventricle choroid plexus with embryonic and postnatal neurogenesis in the hippocampus.

Synthetic PreImplantation Factor (sPIF) reduces inflammation and prevents preterm birth

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality and spontaneous PTB is a major contributor. The preceding inflammation/infection contributes not only to spontaneous PTB but is associated with neonatal morbidities including impaired brain development. Therefore, control of exaggerated immune response during pregnancy is an attractive strategy. A potential candidate is synthetic PreImplantation Factor (sPIF) as sPIF prevents inflammatory induced fetal loss and has neuroprotective properties. Here, we tested maternal sPIF prophylaxis in pregnant mice subjected to a lipopolysaccharides (LPS) insult, which results in PTB. Additionally, we evaluated sPIF effects in placental and microglial cell lines. Maternal sPIF application reduced the LPS induced PTB rate significantly. Consequently, sPIF reduced microglial activation (Iba-1 positive cells) and preserved neuronal migration (Cux-2 positive cells) in fetal brains. In fetal brain lysates sPIF decreased IL-6 and INFγ concentrations. In-vitro, sPIF reduced Iba1 and TNFα expression in microglial cells and reduced the expression of pro-apoptotic (Bad and Bax) and inflammatory (IL-6 and NLRP4) genes in placental cell lines. Together, maternal sPIF prophylaxis prevents PTB in part by controlling exaggerated immune response. Given the sPIF`FDA Fast Track approval in non-pregnant subjects, we envision sPIF therapy in pregnancy.

Modeling Herpes Simplex Virus 1 Infections in Human Central Nervous System Neuronal Cells Using Two- and Three-Dimensional Cultures Derived from Induced Pluripotent Stem Cells

Herpes simplex virus 1 (HSV-1) establishes latency in both peripheral nerve ganglia and the central nervous system (CNS). The outcomes of acute and latent infections in these different anatomic sites appear to be distinct. It is becoming clear that many of the existing culture models using animal primary neurons to investigate HSV-1 infection of the CNS are limited and not ideal, and most do not recapitulate features of CNS neurons. Human induced pluripotent stem cells (hiPSCs) and neurons derived from them are documented as tools to study aspects of neuropathogenesis, but few have focused on modeling infections of the CNS. Here, we characterize functional two-dimensional (2D) CNS-like neuron cultures and three-dimensional (3D) brain organoids made from hiPSCs to model HSV-1-human-CNS interactions. Our results show that (i) hiPSC-derived CNS neurons are permissive for HSV-1 infection; (ii) a quiescent state exhibiting key landmarks of HSV-1 latency described in animal models can be established in hiPSC-derived CNS neurons; (iii) the complex laminar structure of the organoids can be efficiently infected with HSV, with virus being transported from the periphery to the central layers of the organoid; and (iv) the organoids support reactivation of HSV-1, albeit less efficiently than 2D cultures. Collectively, our results indicate that hiPSC-derived neuronal platforms, especially 3D organoids, offer an extraordinary opportunity for modeling the interaction of HSV-1 with the complex cellular and architectural structure of the human CNS.IMPORTANCE This study employed human induced pluripotent stem cells (hiPSCs) to model acute and latent HSV-1 infections in two-dimensional (2D) and three-dimensional (3D) CNS neuronal cultures. We successfully established acute HSV-1 infections and infections showing features of latency. HSV-1 infection of the 3D organoids was able to spread from the outer surface of the organoid and was transported to the interior lamina, providing a model to study HSV-1 trafficking through complex neuronal tissue structures. HSV-1 could be reactivated in both culture systems; though, in contrast to 2D cultures, it appeared to be more difficult to reactivate HSV-1 in 3D cultures, potentially paralleling the low efficiency of HSV-1 reactivation in the CNS of animal models. The reactivation events were accompanied by dramatic neuronal morphological changes and cell-cell fusion. Together, our results provide substantive evidence of the suitability of hiPSC-based neuronal platforms to model HSV-1-CNS interactions in a human context.

Generation of three-dimensional human neuronal cultures: application to modeling CNS viral infections

BACKGROUND

A variety of neurological disorders including neurodegenerative diseases and infection by neurotropic viruses can cause structural and functional changes in the central nervous system (CNS), resulting in long-term neurological sequelae. An improved understanding of the pathogenesis of these disorders is important for developing efficacious interventions. Human induced pluripotent stem cells (hiPSCs) offer an extraordinary window for modeling pathogen-CNS interactions, and other cellular interactions, in three-dimensional (3D) neuronal cultures that can recapitulate several aspects of in vivo brain tissue.

METHODS

Herein, we describe a prototype of scaffold-free hiPSC-based adherent 3D (A-3D) human neuronal cultures in 96-well plates. To test their suitability for drug screening, A-3D neuronal cultures were infected with herpes simplex virus type 1 (HSV-1) with or without acyclovir.

RESULTS

The half maximal inhibitory concentration (IC50) of acyclovir was 3.14 μM and 3.12 μM determined using flow cytometry and the CX7 High Content Screening platform, respectively.

CONCLUSIONS

Our A-3D neuronal cultures provide an unprecedented opportunity for high-content drug screening programs to treat human CNS infections.

The epilepsy phenotypic spectrum associated with a recurrent CUX2 variant

OBJECTIVE

Cut homeodomain transcription factor CUX2 plays an important role in dendrite branching, spine development, and synapse formation in layer II to III neurons of the cerebral cortex. We identify a recurrent de novo CUX2 p.Glu590Lys as a novel genetic cause for developmental and epileptic encephalopathy (DEE).

METHODS

The de novo p.Glu590Lys variant was identified by whole-exome sequencing (n = 5) or targeted gene panel (n = 4). We performed electroclinical and imaging phenotyping on all patients.

RESULTS

The cohort comprised 7 males and 2 females. Mean age at study was 13 years (0.5-21.0). Median age at seizure onset was 6 months (2 months to 9 years). Seizure types at onset were myoclonic, atypical absence with myoclonic components, and focal seizures. Epileptiform activity on electroencephalogram was seen in 8 cases: generalized polyspike-wave (6) or multifocal discharges (2). Seizures were drug resistant in 7 or controlled with valproate (2). Six patients had a DEE: myoclonic DEE (3), Lennox-Gastaut syndrome (2), and West syndrome (1). Two had a static encephalopathy and genetic generalized epilepsy, including absence epilepsy in 1. One infant had multifocal epilepsy. Eight had severe cognitive impairment, with autistic features in 6. The p.Glu590Lys variant affects a highly conserved glutamine residue in the CUT domain predicted to interfere with CUX2 binding to DNA targets during neuronal development.

INTERPRETATION

Patients with CUX2 p.Glu590Lys display a distinctive phenotypic spectrum, which is predominantly generalized epilepsy, with infantile-onset myoclonic DEE at the severe end and generalized epilepsy with severe static developmental encephalopathy at the milder end of the spectrum. Ann Neurol 2018;83:926-934.

The crux of Cux genes in neuronal function and plasticity

Cux1 and Cux2 are the vertebrate members of a family of homeodomain transcription factors (TF) containing Cut repeat DNA-binding sequences. Perturbation of their expression has been implicated in a wide variety of diseases and disorders, ranging from cancer to autism spectrum disorder (ASD). Within the nervous system, both genes are expressed during neurogenesis and in specific neuronal subpopulations. Their role during development and circuit specification is discussed here, with a particular focus on the cortex where their restricted expression in pyramidal neurons of the upper layers appears to be responsible for many of the specialized functions of these cells, and where their functions have been extensively investigated. Finally, we discuss how Cux TF represent a promising avenue for manipulating neuronal function and for reprogramming.

Observations on hippocampal mossy cells in mink (Neovison vison) with special reference to dendrites ascending to the granular and molecular layers

Detailed knowledge about the neural circuitry connecting the hippocampus and entorhinal cortex is necessary to understand how this system contributes to spatial navigation and episodic memory. The two principal cell types of the dentate gyrus, mossy cells and granule cells, are interconnected in a positive feedback loop, by which mossy cells can influence information passing from the entorhinal cortex via granule cells to hippocampal pyramidal cells. Mossy cells, like CA3 pyramidal cells, are characterized by thorny excrescences on their proximal dendrites, postsynaptic to giant terminals of granule cell axons. In addition to disynaptic input from the entorhinal cortex and perforant path via granule cells, mossy cells may also receive monosynaptic input from the perforant path via special dendrites ascending to the molecular layer. We here report qualitative and quantitative descriptions of Golgi-stained hippocampal mossy cells in mink, based on light microscopic observations and three-dimensional reconstructions. The main focus is on the location, branching pattern, and length of dendrites, particularly those ascending to the granular and molecular layers. In mink, the latter dendrites are more numerous than in rat, but fewer than in primates. They form on average 12% (and up to 29%) of the total dendritic length, and appear to cover the terminal fields of both the lateral and medial perforant paths. In further contrast to rat, the main mossy cell dendrites in mink branch more extensively with distal dendrites encroaching upon the CA3 field. The dendritic arbors extend both along and across the septotemporal axis of the dentate gyrus, not conforming to the lamellar pattern of the hippocampus. The findings suggest that the afferent input to the mossy cells becomes more complex in species closer to primates.

CUX2 protein functions as an accessory factor in the repair of oxidative DNA damage

CUX1 and CUX2 proteins are characterized by the presence of three highly similar regions called Cut repeats 1, 2, and 3. Although CUX1 is ubiquitously expressed, CUX2 plays an important role in the specification of neuronal cells and continues to be expressed in postmitotic neurons. Cut repeats from the CUX1 protein were recently shown to stimulate 8-oxoguanine DNA glycosylase 1 (OGG1), an enzyme that removes oxidized purines from DNA and introduces a single strand break through its apurinic/apyrimidinic lyase activity to initiate base excision repair. Here, we investigated whether CUX2 plays a similar role in the repair of oxidative DNA damage. Cux2 knockdown in embryonic cortical neurons increased levels of oxidative DNA damage. In vitro, Cut repeats from CUX2 increased the binding of OGG1 to 7,8-dihydro-8-oxoguanine-containing DNA and stimulated both the glycosylase and apurinic/apyrimidinic lyase activities of OGG1. Genetic inactivation in mouse embryo fibroblasts or CUX2 knockdown in HCC38 cells delayed DNA repair and increased DNA damage. Conversely, ectopic expression of Cut repeats from CUX2 accelerated DNA repair and reduced levels of oxidative DNA damage. These results demonstrate that CUX2 functions as an accessory factor that stimulates the repair of oxidative DNA damage. Neurons produce a high level of reactive oxygen species because of their dependence on aerobic oxidation of glucose as their source of energy. Our results suggest that the persistent expression of CUX2 in postmitotic neurons contributes to the maintenance of genome integrity through its stimulation of oxidative DNA damage repair.