Disruption of the Extracellular Matrix Progressively Impairs Central Nervous System Vascular Maturation Downstream of β-Catenin Signaling.

Objective- The Wnt/β-catenin pathway orchestrates development of the blood-brain barrier, but the downstream mechanisms involved at different developmental windows and in different central nervous system (CNS) tissues have remained elusive. Approach and Results- Here, we create a new mouse model allowing spatiotemporal investigations of Wnt/β-catenin signaling by induced overexpression of Axin1, an inhibitor of β-catenin signaling, specifically in endothelial cells ( Axin1 - ). AOE (Axin1 overexpression) in Axin1 - mice at stages following the initial vascular invasion of the CNS did not impair angiogenesis but led to premature vascular regression followed by progressive dilation and inhibition of vascular maturation resulting in forebrain-specific hemorrhage 4 days post-AOE.

Gene expression profiles of brain endothelial cells during embryonic development at bulk and single-cell levels.

The blood-brain barrier is a dynamic interface that separates the brain from the circulatory system, and it is formed by highly specialized endothelial cells. To explore the molecular mechanisms defining the unique nature of vascular development and differentiation in the brain, we generated high-resolution gene expression profiles of mouse embryonic brain endothelial cells using translating ribosome affinity purification and single-cell RNA sequencing. We compared the brain vascular translatome with the vascular translatomes of other organs and analyzed the vascular translatomes of the brain at different time points during embryonic development.

Apolipoprotein C-I mediates Wnt/Ctnnb1 signaling during neural border formation and is required for neural crest development.

In vertebrates, the neural crest and placodes originate in the neural border, which is located between the neural plate and epidermal ectoderm. The neural crest and placodes give rise to a vast array of cell types. Formation of neural crest is a multi-step process, in which Wnt signals are used reiteratively, but it is currently not clear if a Wnt signal is required for neural border formation.

Evaluation of TRAP-sequencing technology with a versatile conditional mouse model.

Gene expression profiling of various cell lineages has provided invaluable insights into the molecular mechanisms regulating cellular development and differentiation. However, in vivo molecular profiling of rare and interspersed cell populations, such as endothelial cells, has remained challenging. We have generated a versatile floxed translating ribosome affinity purification (TRAP) mouse model, mCherryTRAP, for Cre-dependent translational profiling of distinct cell lineages from intact tissues.

Canonical Wnt signaling regulates organ-specific assembly and differentiation of CNS vasculature.

Every organ depends on blood vessels for oxygen and nutrients, but the vasculature associated with individual organs can be structurally and molecularly diverse. The central nervous system (CNS) vasculature consists of a tightly sealed endothelium that forms the blood-brain barrier, whereas blood vessels of other organs are more porous. Wnt7a and Wnt7b encode two Wnt ligands produced by the neuroepithelium of the developing CNS coincident with vascular invasion.

Mouse brain organization revealed through direct genome-scale TF expression analysis.

In the developing brain, transcription factors (TFs) direct the formation of a diverse array of neurons and glia. We identifed 1445 putative TFs in the mouse genome. We used in situ hybridization to map the expression of over 1000 of these TFs and TF-coregulator genes in the brains of developing mice.

Sequential phases of cortical specification involve Neurogenin-dependent and -independent pathways.

Neocortical projection neurons, which segregate into six cortical layers according to their birthdate, have diverse morphologies, axonal projections and molecular profiles, yet they share a common cortical regional identity and glutamatergic neurotransmission phenotype. Here we demonstrate that distinct genetic programs operate at different stages of corticogenesis to specify the properties shared by all neocortical neurons. Ngn1 and Ngn2 are required to specify the cortical (regional), glutamatergic (neurotransmitter) and laminar (temporal) characters of early-born (lower-layer) neurons, while simultaneously repressing an alternative subcortical, GABAergic neuronal phenotype.

Tlx controls proliferation and patterning of lateral telencephalic progenitor domains.

We showed previously that the orphan nuclear receptor Tlx is required for the correct establishment of the pallio-subpallial boundary. Loss of Tlx results in a dorsal expansion of ventral markers (e.g.