Islet1 Precursors Contribute to Mature Interneuron Subtypes in Mouse Neocortex.

Cortical interneurons (GABAergic cells) arise during embryogenesis primarily from the medial and caudal ganglionic eminences (MGE and CGE, respectively) with a small population generated from the preoptic area (POA). Progenitors from the lateral ganglionic eminence (LGE) are thought to only generate GABAergic medium spiny neurons that populate the striatum and project to the globus pallidus. Here, we report evidence that neuronal precursors that express the LGE-specific transcription factor Islet1 (Isl1) can give rise to a small population of cortical interneurons. Lineage tracing and homozygous deletion of Nkx2.1 in Isl1 fate-mapped mice showed that neighboring MGE/POA-specific Nkx2.1 cells and LGE-specific Isl1 cells make both common and distinct lineal contributions towards cortical interneuron fate. Although the majority of cells had overlapping transcriptional domains between Nkx2.1 and Isl1, a population of Isl1-only derived cells also contributed to the adult cerebral cortex. The data indicate that Isl1-derived cells may originate from both the LGE and the adjacent LGE/MGE boundary regions to generate diverse neuronal progeny. Thus, a small population of neocortical interneurons appear to originate from Isl-1-positive precursors.

Malformation of the Posterior Cerebellar Vermis Is a Common Neuroanatomical Phenotype of Genetically Engineered Mice on the C57BL/6 Background.

C57BL/6 mice exhibit spontaneous cerebellar malformations consisting of heterotopic neurons and glia in the molecular layer of the posterior vermis, indicative of neuronal migration defect during cerebellar development. Recognizing that many genetically engineered (GE) mouse lines are produced from C57BL/6 ES cells or backcrossed to this strain, we performed histological analyses and found that cerebellar heterotopia were a common feature present in the majority of GE lines on this background. Furthermore, we identify GE mouse lines that will be valuable in the study of cerebellar malformations including diverse driver, reporter, and optogenetic lines. Finally, we discuss the implications that these data have on the use of C57BL/6 mice and GE mice on this background in studies of cerebellar development or as models of disease.

Stem Cell Therapy for the Central Nervous System in Lysosomal Storage Diseases.

Neurological diseases with genetic etiologies result in the loss or dysfunction of neural cells throughout the CNS. At present, few treatment options exist for the majority of neurogenetic diseases. Stem cell transplantation (SCT) into the CNS has the potential to be an effective treatment modality because progenitor cells may replace lost cells in the diseased brain, provide multiple trophic factors, or deliver missing proteins. This review focuses on the use of SCT in lysosomal storage diseases (LSDs), a large group of monogenic disorders with prominent CNS disease. In most patients the CNS disease results in intellectual disability that is refractory to current standard-of-care treatment. A large amount of preclinical work on brain-directed SCT has been performed in rodent LSD models. Cell types that have been used for direct delivery into the CNS include neural stem cells, embryonic and induced pluripotent stem cells, and mesenchymal stem cells. Hematopoietic stem cells have been an effective therapy for the CNS in a few LSDs and may be augmented by overexpression of the missing gene. Current barriers and potential strategies to improve SCT for translation into effective patient therapies are discussed.

Fate mapping by piggyBac transposase reveals that neocortical GLAST+ progenitors generate more astrocytes than Nestin+ progenitors in rat neocortex.

Progenitors within the neocortical ventricular zone (VZ) first generate pyramidal neurons and then astrocytes. We applied novel piggyBac transposase lineage tracking methods to fate-map progenitor populations positive for Nestin or glutamate and aspartate transpoter (GLAST) promoter activities in the rat neocortex. GLAST+ and Nestin+ progenitors at embryonic day 13 (E13) produce lineages containing similar rations of neurons and astrocytes. By E15, the GLAST+ progenitor population diverges significantly to produce lineages with 5-10-fold more astrocytes relative to neurons than generated by the Nestin+ population. To determine when birth-dated progeny within GLAST+ and Nestin+ populations diverge, we used a Cre/loxP fate-mapping system in which plasmids are lost after a cell division. By E18, birth-dated progeny of GLAST+ progenitors give rise to 2-3-fold more neocortical astrocytes than do Nestin+ progenitors. Finally, we used a multicolor clonal labeling method to show that the GLAST+ population labeled at E15 generates astrocyte progenitors that produce larger, spatially restricted, clonal clusters than the Nestin+ population. This study provides in vivo evidence that by mid-corticogenesis (E15), VZ progenitor populations have significantly diversified in terms of their potential to generate astrocytes and neurons.

The role of DCX and LIS1 in migration through the lateral cortical stream of developing forebrain.

During forebrain development the lateral cortical stream (LCS) supplies neurons to structures in the ventral telencephalon including the amygdala and piriform cortex. In the current study, we used spatially directed in utero electroporation and RNAi to investigate mechanisms of migration to the ventral telencephalon. Cells labeled by in utero electroporation of the lateral ventricular zone migrated into the LCS, and entered the lateral neocortex, piriform cortex and amygdala, where they differentiated primarily as pyramidal neurons. RNAi of DCX or LIS1 disrupted migration into amygdala and piriform cortex and caused many neurons to accumulate in the external and amygdalar capsules. RNAi of LIS1 and DCX had similar as well as distinguishable effects on the pattern of altered migration. Combinatorial RNAi of LIS1 and DCX further suggested interaction in the functions of LIS1 and DCX on the morphology and migration of migrating neurons in the LCS. Together, these results confirm that the LCS contributes pyramidal neurons to ventral forebrain structures and reveals that DCX and LIS1 have important functions in this major migratory pathway in the developing forebrain.

Fusion of microglia with pyramidal neurons after retroviral infection.

The neurogenic potential of the postnatal neocortex has not been tested previously with a combination of both retroviral and bromodeoxyuridine (BrdU) labeling. Here we report that injections of enhanced green fluorescent protein (eGFP) retrovirus into 134 postnatal rats resulted in GFP labeling of 642 pyramidal neurons in neocortex. GFP-labeled neocortical pyramidal neurons, however, unlike GFP-labeled glia, did not incorporate BrdU. Closer inspection of retrovirally labeled neurons revealed microglia fused to the apical dendrites of labeled pyramidal neurons. Retroviral infection of mixed cultures of cortical neurons and glia confirmed the presence of specific neuronal-microglial fusions. Microglia did not fuse to other glial cell types, and cultures not treated with retrovirus lacked microglial-neuronal fusion. Furthermore, activation of microglia by lipopolysaccharide greatly increased the virally induced fusion of microglia to neurons in culture. These results indicate a novel form of specific cell fusion between neuronal dendrites and microglia and further illustrate the need for caution when interpreting evidence for neuronogenesis in the postnatal brain.

Brain atrophy in mild or moderate traumatic brain injury: a longitudinal quantitative analysis.

BACKGROUND AND PURPOSE: Although mild or moderate traumatic brain injury (TBI) is known to cause persistent neurologic sequelae, the underlying structural changes remain elusive. Our purpose was to assess decreases in the volume of brain parenchyma (VBP) in patients with TBI and to determine if clinical parameters are predictors of the extent of atrophy. METHODS: We retrospectively assessed the total VBP in 14 patients with mild or moderate TBI at more than 3 months after injury and in seven patients at two time points more than 3 months apart. VBP was calculated from whole-brain MR images and then normalized by calculating the percent VBP (%VBP) to correct for intraindividual variations in cranial size. Clinical parameters at the time of trauma were evaluated for potential predictors of atrophy. Findings were compared with those of control subjects of similar ages. RESULTS: In the single time-point analysis, brain volumes, CSF volumes, and %VBP were not significantly different between patients and control subjects. In the longitudinal analysis, the rate of decline in %VBP (0.02 versus 0.0064 U/day, P =.05) and the change in %VBP between the first and second time points (-4.16 +/- 1.68 versus -1.49 +/- 1.7, P =.022 [mean +/-SD]) were significantly greater in patients. Change in %VBP was significantly greater in patients with loss of consciousness (LOC) than in those without LOC (P =.023). CONCLUSION: Whole-brain atrophy occurs after mild or moderate TBI and is evident at an average of 11 months after trauma. Injury that produces LOC leads to more atrophy. These findings may help elucidate an etiology for the persistent or new neurologic deficits that occur months after injury.