Pharmacogenomic identification of small molecules for lineage specific manipulation of subventricular zone germinal activity.

Strategies for promoting neural regeneration are hindered by the difficulty of manipulating desired neural fates in the brain without complex genetic methods. The subventricular zone (SVZ) is the largest germinal zone of the forebrain and is responsible for the lifelong generation of interneuron subtypes and oligodendrocytes. Here, we have performed a bioinformatics analysis of the transcriptome of dorsal and lateral SVZ in early postnatal mice, including neural stem cells (NSCs) and their immediate progenies, which generate distinct neural lineages. We identified multiple signaling pathways that trigger distinct downstream transcriptional networks to regulate the diversity of neural cells originating from the SVZ. Next, we used a novel in silico genomic analysis, searchable platform-independent expression database/connectivity map (SPIED/CMAP), to generate a catalogue of small molecules that can be used to manipulate SVZ microdomain-specific lineages. Finally, we demonstrate that compounds identified in this analysis promote the generation of specific cell lineages from NSCs in vivo, during postnatal life and adulthood, as well as in regenerative contexts. This study unravels new strategies for using small bioactive molecules to direct germinal activity in the SVZ, which has therapeutic potential in neurodegenerative diseases.

Neonatal brain injury unravels transcriptional and signaling changes underlying the reactivation of cortical progenitors.

Germinal activity persists throughout life within the ventricular-subventricular zone (V-SVZ) of the postnatal forebrain due to the presence of neural stem cells (NSCs). Accumulating evidence points to a recruitment for these cells following early brain injuries and suggests their amenability to manipulations. We used chronic hypoxia as a rodent model of early brain injury to investigate the reactivation of cortical progenitors at postnatal times. Our results reveal an increased proliferation and production of glutamatergic progenitors within the dorsal V-SVZ. Fate mapping of V-SVZ NSCs demonstrates their contribution to de novo cortical neurogenesis. Transcriptional analysis of glutamatergic progenitors shows parallel changes in methyltransferase 14 (Mettl14) and Wnt/ß-catenin signaling. In agreement, manipulations through genetic and pharmacological activation of Mettl14 and the Wnt/ß-catenin pathway, respectively, induce neurogenesis and promote newly-formed cell maturation. Finally, labeling of young adult NSCs demonstrates that pharmacological NSC activation has no adverse effects on the reservoir of V-SVZ NSCs and on their germinal activity.

Transcriptional Dysregulation in Postnatal Glutamatergic Progenitors Contributes to Closure of the Cortical Neurogenic Period.

Progenitors of cortical glutamatergic neurons (Glu progenitors) are usually thought to switch fate before birth to produce astrocytes. We used fate-mapping approaches to show that a large fraction of Glu progenitors persist in the postnatal forebrain after closure of the cortical neurogenesis period. Postnatal Glu progenitors do not accumulate during embryonal development but are produced by embryonal radial glial cells that persist after birth in the dorsal subventricular zone and continue to give rise to cortical neurons, although with low efficiency. Single-cell RNA sequencing reveals a dysregulation of transcriptional programs, which parallels changes in m6A methylation and correlates with the gradual decline in cortical neurogenesis observed in vivo. Rescuing experiments show that postnatal progenitors are partially permissive to genetic and pharmacological manipulations. Our study provides an in-depth characterization of postnatal Glu progenitors and identifies potential therapeutic targets for promoting brain repair.

Nkd1 functions as a passive antagonist of Wnt signaling.

Wnt signaling is involved in many aspects of development and in the homeostasis of stem cells. Its importance is underscored by the fact that misregulation of Wnt signaling has been implicated in numerous diseases, especially colorectal cancer. However, how Wnt signaling regulates itself is not well understood. There are several Wnt negative feedback regulators, which are active antagonists of Wnt signaling, but one feedback regulator, Nkd1, has reduced activity compared to other antagonists, yet is still a negative feedback regulator. Here we describe our efforts to understand the role of Nkd1 using Wnt signaling compromised zebrafish mutant lines. In several of these lines, Nkd1 function was not any more active than it was in wild type embryos. However, we found that Nkd1's ability to antagonize canonical Wnt/ß-catenin signaling was enhanced in the Wnt/Planar Cell Polarity mutants silberblick (slb/wnt11) and trilobite (tri/vangl2). While slb and tri mutants do not display alterations in canonical Wnt signaling, we found that they are hypersensitive to it. Overexpression of the canonical Wnt/ß-catenin ligand Wnt8a in slb or tri mutants resulted in dorsalized embryos, with tri mutants being much more sensitive to Wnt8a than slb mutants. Furthermore, the hyperdorsalization caused by Wnt8a in tri could be rescued by Nkd1. These results suggest that Nkd1 functions as a passive antagonist of Wnt signaling, functioning only when homeostatic levels of Wnt signaling have been breached or when Wnt signaling becomes destabilized.