FOXG1 targets BMP repressors and cell cycle inhibitors in human neural progenitor cells.

FOXG1 is a critical transcription factor in human brain where loss-of-function mutations cause a severe neurodevelopmental disorder, while increased FOXG1 expression is frequently observed in glioblastoma. FOXG1 is an inhibitor of cell patterning and an activator of cell proliferation in chordate model organisms but different mechanisms have been proposed as to how this occurs. To identify genomic targets of FOXG1 in human neural progenitor cells (NPCs), we engineered a cleavable reporter construct in endogenous FOXG1 and performed chromatin immunoprecipitation (ChIP) sequencing. We also performed deep RNA sequencing of NPCs from two females with loss-of-function mutations in FOXG1 and their healthy biological mothers. Integrative analyses of RNA and ChIP sequencing data showed that cell cycle regulation and Bone Morphogenic Protein (BMP) repression gene ontology categories were over-represented as FOXG1 targets. Using engineered brain cell lines, we show that FOXG1 specifically activates SMAD7 and represses CDKN1B. Activation of SMAD7 which inhibits BMP signaling may be one way that FOXG1 patterns the forebrain, while repression of cell cycle regulators such as CDKN1B may be one way that FOXG1 expands the NPC pool to ensure proper brain size. Our data reveal novel mechanisms on how FOXG1 may control forebrain patterning and cell proliferation in human brain development.

Kabuki syndrome stem cell models reveal locus specificity of histone methyltransferase 2D (KMT2D/MLL4).

Kabuki syndrome is frequently caused by loss-of-function mutations in one allele of histone 3 lysine 4 (H3K4) methyltransferase KMT2D and is associated with problems in neurological, immunological and skeletal system development. We generated heterozygous KMT2D knockout and Kabuki patient-derived cell models to investigate the role of reduced dosage of KMT2D in stem cells. We discovered chromosomal locus-specific alterations in gene expression, specifically a 110 Kb region containing Synaptotagmin 3 (SYT3), C-Type Lectin Domain Containing 11A (CLEC11A), Chromosome 19 Open Reading Frame 81 (C19ORF81) and SH3 And Multiple Ankyrin Repeat Domains 1 (SHANK1), suggesting locus-specific targeting of KMT2D. Using whole genome histone methylation mapping, we confirmed locus-specific changes in H3K4 methylation patterning coincident with regional decreases in gene expression in Kabuki cell models. Significantly reduced H3K4 peaks aligned with regions of stem cell maps of H3K27 and H3K4 methylation suggesting KMT2D haploinsufficiency impact bivalent enhancers in stem cells. Preparing the genome for subsequent differentiation cues may be of significant importance for Kabuki-related genes. This work provides a new insight into the mechanism of action of an important gene in bone and brain development and may increase our understanding of a specific function of a human disease-relevant H3K4 methyltransferase family member.

Evidence That Substantia Nigra Pars Compacta Dopaminergic Neurons Are Selectively Vulnerable to Oxidative Stress Because They Are Highly Metabolically Active.

There are 400-500 thousand dopaminergic cells within each side of the human substantia nigra pars compacta (SNpc) making them a minuscule portion of total brain mass. These tiny clusters of cells have an outsized impact on motor output and behavior as seen in disorders such as Parkinson's disease (PD). SNpc dopaminergic neurons are more vulnerable to oxidative stress compared to other brain cell types, but the reasons for this are not precisely known. Here we provide evidence to support the hypothesis that this selective vulnerability is because SNpc neurons sustain high metabolic rates compared to other neurons. A higher baseline requirement for ATP production may lead to a selective vulnerability to impairments in oxidative phosphorylation (OXPHOS) or genetic insults that impair Complex I of the electron transport chain. We suggest that the energy demands of the unique morphological and electrophysiological properties of SNpc neurons may be one reason these cells produce more ATP than other cells. We further provide evidence to support the hypothesis that transcription factors (TFs) required to drive induction, differentiation, and maintenance of midbrain dopaminergic neural progenitor cells which give rise to terminally differentiated SNpc neurons are uniquely involved in both developmental patterning and metabolism, a dual function unlike other TFs that program neurons in other brain regions. The use of these TFs during induction and differentiation may program ventral midbrain progenitor cells metabolically to higher ATP levels, allowing for the development of those specialized cell processes seen in terminally differentiated cells. This paper provides a cellular and developmental framework for understanding the selective vulnerability of SNpc dopaminergic cells to oxidative stress.

FOXG1 dose tunes cell proliferation dynamics in human forebrain progenitor cells.

Heterozygous loss-of-function mutations in Forkhead box G1 (FOXG1), a uniquely brain-expressed gene, cause microcephaly, seizures, and severe intellectual disability, whereas increased FOXG1 expression is frequently observed in glioblastoma. To investigate the role of FOXG1 in forebrain cell proliferation, we modeled FOXG1 syndrome using cells from three clinically diagnosed cases with two sex-matched healthy parents and one unrelated sex-matched control. Cells with heterozygous FOXG1 loss showed significant reduction in cell proliferation, increased ratio of cells in G0/G1 stage of the cell cycle, and increased frequency of primary cilia. Engineered loss of FOXG1 recapitulated this effect, while isogenic repair of a patient mutation reverted output markers to wild type. An engineered inducible FOXG1 cell line derived from a FOXG1 syndrome case demonstrated that FOXG1 dose-dependently affects all cell proliferation outputs measured. These findings provide strong support for the critical importance of FOXG1 levels in controlling human brain cell growth in health and disease.

The BDNF val66met polymorphism is associated with decreased use of landmarks and decreased fMRI activity in the hippocampus during virtual navigation.

People can navigate in a new environment using multiple strategies dependent on different memory systems. A series of studies have dissociated between hippocampus-dependent 'spatial' navigation and habit-based 'response' learning mediated by the caudate nucleus. The val66met polymorphism of the brain-derived neurotrophic factor (BDNF) gene leads to decreased secretion of BDNF in the brain, including the hippocampus. Here, we aim to investigate the role of the BDNF val66met polymorphism on virtual navigation behaviour and brain activity in healthy older adults. A total of 139 healthy older adult participants (mean age = 65.8 ± 4.4 years) were tested in this study. Blood samples were collected, and BDNF val66met genotyping was performed. Participants were divided into two genotype groups: val homozygotes and met carriers. Participants were tested on virtual dual-solution navigation tasks in which they could use either a hippocampus-dependent spatial strategy or a caudate nucleus-dependent response strategy to solve the task. A subset of the participants (n = 66) were then scanned in a 3T functional magnetic resonance imaging (fMRI) scanner while engaging in another dual-solution navigation task. BDNF val/val individuals and met carriers did not differ in learning performance. However, the two BDNF groups differed in learning strategy. BDNF val/val individuals relied more on landmarks to remember target locations (i.e., increased use of flexible spatial learning), while met carriers relied more on sequences and patterns to remember target locations (i.e., increased use of inflexible response learning). Additionally, BDNF val/val individuals had more fMRI activity in the hippocampus compared with BDNF met carriers during performance on the navigation task. This is the first study to show in older adults that BDNF met carriers use alternate learning strategies from val/val individuals and to identify differential brain activation of this behavioural difference between the two groups.