A comparative evaluation of the strengths and potential caveats of the microglial inducible CreER mouse models.

The recent proliferation of new Cre and CreER recombinase lines provides researchers with a diverse toolkit to study microglial gene function. To determine how best to apply these lines in studies of microglial gene function, a thorough and detailed comparison of their properties is needed. Here, we examined four different microglial CreER lines (Cx3cr1, Cx3cr1, P2ry12, and Tmem119), focusing on (1) recombination specificity, (2) leakiness (the degree of tamoxifen-independent recombination in microglia and other cells), (3) the efficiency of tamoxifen-induced recombination, (4) extraneural recombination (the degree of recombination in cells outside of the CNS, particularly myelo/monocyte lineages), and (5) off-target effects in the context of neonatal brain development.

Radial glia promote microglial development through integrin αβ -TGFβ1 signaling.

Microglia diversity emerges from interactions between intrinsic genetic programs and environment-derived signals, but how these processes unfold and interact in the developing brain remains unclear. Here, we show that radial glia-expressed integrin beta 8 (ITGB8) expressed in radial glia progenitors activates microglia-expressed TGFβ1, permitting microglial development. Domain-restricted deletion of in these progenitors establishes complementary regions with developmentally arrested "dysmature" microglia that persist into adulthood.

APOE4 impairs the microglial response in Alzheimer's disease by inducing TGFβ-mediated checkpoints.

The APOE4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). The contribution of microglial APOE4 to AD pathogenesis is unknown, although APOE has the most enriched gene expression in neurodegenerative microglia (MGnD). Here, we show in mice and humans a negative role of microglial APOE4 in the induction of the MGnD response to neurodegeneration.

Single cell enhancer activity distinguishes GABAergic and cholinergic lineages in embryonic mouse basal ganglia.

Enhancers integrate transcription factor signaling pathways that drive cell fate specification in the developing brain. We paired enhancer labeling and single-cell RNA-sequencing (scRNA-seq) to delineate and distinguish specification of neuronal lineages in mouse medial, lateral, and caudal ganglionic eminences (MGE, LGE, and CGE) at embryonic day (E)11.5.

A new genetic strategy for targeting microglia in development and disease.

As the resident macrophages of the brain and spinal cord, microglia are crucial for the phagocytosis of infectious agents, apoptotic cells and synapses. During brain injury or infection, bone-marrow derived macrophages invade neural tissue, making it difficult to distinguish between invading macrophages and resident microglia. In addition to circulation-derived monocytes, other non-microglial central nervous system (CNS) macrophage subtypes include border-associated meningeal, perivascular and choroid plexus macrophages.

Lack of Flvcr2 impairs brain angiogenesis without affecting the blood-brain barrier.

Fowler syndrome is a rare autosomal recessive brain vascular disorder caused by mutation in FLVCR2 in humans. The disease occurs during a critical period of brain vascular development, is characterized by glomeruloid vasculopathy and hydrocephalus, and is almost invariably prenatally fatal. Here, we sought to gain insights into the process of brain vascularization and the pathogenesis of Fowler syndrome by inactivating Flvcr2 in mice.

Functionally Distinct Connectivity of Developmentally Targeted Striosome Neurons.

One long-standing model of striatal function divides the striatum into compartments called striosome and matrix. While some anatomical evidence suggests that these populations represent distinct striatal pathways with differing inputs and outputs, functional investigation has been limited by the methods for identifying and manipulating these populations. Here, we utilize hs599 mice as a new tool for targeting striosome projection neurons and testing their functional connectivity.

Genomic Resolution of DLX-Orchestrated Transcriptional Circuits Driving Development of Forebrain GABAergic Neurons.

DLX transcription factors (TFs) are master regulators of the developing vertebrate brain, driving forebrain GABAergic neuronal differentiation. Ablation of Dlx1&2 alters expression of genes that are critical for forebrain GABAergic development. We integrated epigenomic and transcriptomic analyses, complemented with in situ hybridization (ISH), and in vivo and in vitro studies of regulatory element (RE) function.

Mafb and c-Maf Have Prenatal Compensatory and Postnatal Antagonistic Roles in Cortical Interneuron Fate and Function.

Mafb and c-Maf transcription factor (TF) expression is enriched in medial ganglionic eminence (MGE) lineages, beginning in late-secondary progenitors and continuing into mature parvalbumin (PV) and somatostatin (SST) interneurons. However, the functions of Maf TFs in MGE development remain to be elucidated. Herein, Mafb and c-Maf were conditionally deleted, alone and together, in the MGE and its lineages.

Subpallial Enhancer Transgenic Lines: a Data and Tool Resource to Study Transcriptional Regulation of GABAergic Cell Fate.

Elucidating the transcriptional circuitry controlling forebrain development requires an understanding of enhancer activity and regulation. We generated stable transgenic mouse lines that express CreER and GFP from ten different enhancer elements with activity in distinct domains within the embryonic basal ganglia. We used these unique tools to generate a comprehensive regional fate map of the mouse subpallium, including sources for specific subtypes of amygdala neurons.

Disruptions in a cluster of computationally identified enhancers near FOXC1 and GMDS may influence brain development.

Regulatory elements are more evolutionarily conserved and provide a larger mutational target than coding regions of the human genome, suggesting that mutations in non-coding regions contribute significantly to development and disease. Using a computational approach to predict gene regulatory enhancers, we found that many known and predicted embryonic enhancers cluster in genomic loci harboring development-associated genes. One of the densest clusters of predicted enhancers in the human genome is near the genes GMDS and FOXC1.

Olig1 function is required to repress dlx1/2 and interneuron production in Mammalian brain.

Abnormal GABAergic interneuron density, and imbalance of excitatory versus inhibitory tone, is thought to result in epilepsy, neurodevelopmental disorders, and psychiatric disease. Recent studies indicate that interneuron cortical density is determined primarily by the size of the precursor pool in the embryonic telencephalon. However, factors essential for regulating interneuron allocation from telencephalic multipotent precursors are poorly understood.

Fezf2 expression identifies a multipotent progenitor for neocortical projection neurons, astrocytes, and oligodendrocytes.

Progenitor cells in the cerebral cortex sequentially generate distinct classes of projection neurons. Recent work suggests the cortex may contain intrinsically fate-restricted progenitors marked by expression of Cux2. However, the heterogeneity of the neocortical ventricular zone as well as the contribution of lineage-restricted progenitors to the overall cortical neurogenic program remains unclear.

A high-resolution enhancer atlas of the developing telencephalon.

The mammalian telencephalon plays critical roles in cognition, motor function, and emotion. Though many of the genes required for its development have been identified, the distant-acting regulatory sequences orchestrating their in vivo expression are mostly unknown. Here, we describe a digital atlas of in vivo enhancers active in subregions of the developing telencephalon.

Dlx1&2-dependent expression of Zfhx1b (Sip1, Zeb2) regulates the fate switch between cortical and striatal interneurons.

Mammalian pallial (cortical and hippocampal) and striatal interneurons are both generated in the embryonic subpallium, including the medial ganglionic eminence (MGE). Herein we demonstrate that the Zfhx1b (Sip1, Zeb2) zinc finger homeobox gene is required in the MGE, directly downstream of Dlx1&2, to generate cortical interneurons that express Cxcr7, MafB, and cMaf. In its absence, Nkx2-1 expression is not repressed, and cells that ordinarily would become cortical interneurons appear to transform toward a subtype of GABAergic striatal interneurons.

Generation of Cre-transgenic mice using Dlx1/Dlx2 enhancers and their characterization in GABAergic interneurons.

DLX1 and DLX2 transcription factors are necessary for forebrain GABAergic neuron differentiation, migration, and survival. We generated transgenic mice that express Cre-recombinase under the control of two ultra-conserved DNA elements near the Dlx1 and 2 locus termed I12b and URE2. We show that Cre-recombinase is active in a "Dlx-pattern" in the embryonic forebrain of transgenic mice.