Biology subjects

Ghazale, H.

Publications and source records attributed to Ghazale, H..

4 recordsLinked to original sources

bioRxiv2025

Hippo/YAP1 Signaling Regulates the Oligodendrocyte-Astrocyte Fate Switch and Ependymal Gene Expression in Adult Spinal Cord Stem Cells

The adult mammalian spinal cord harbors ependymal cells that retain neural stem-cell properties. Although they possess a latent capacity to generate oligodendrocytes, these cells predominantly differentiate into astrocytes after injury. The molecular cues that govern their lineage commitment toward astrocytic versus oligodendroglial fates remain poorly defined. In this study, we addressed this gap in vitro by investigating the emergence of PDGFRA oligodendrocyte precursor cells (OPCs) in neurosphere cultures derived from adult spinal cord stem cells. We first observed that neurosphere cells exhibited a hybrid identity, co-expressing transcription factors of both astrocytic (NFIA, SOX9) and oligodendrocytic (OLIG1/2, SOX4, NKX2.2, TCF4) lineages. Upon differentiation, oligodendrocytic transcription factors were selectively maintained in OPCs but reduced in other cells. Using PdgfraH2B-GFP mice, we then isolated newly formed PDGFRA OPCs from neurospheres and performed multi-omic profiling. OPC formation was associated with the upregulation of chromatin remodelers and the downregulation of stem-cell markers such as EGFR, HES1, and TNC. Strikingly, OPC specification coincided with reduced expression of YAP1 and its partner TEAD1, key effectors of the Hippo pathway. Functional analyses revealed that YAP1 loss enhanced oligodendrocytic differentiation while reducing astrocytic and ependymal/cilia-associated gene expression. Conversely, constitutive YAP1 activation blocked differentiation into both lineages and promoted an ependymal-like transcriptional program, including upregulation of the ependymal marker CD24a and cilia-related proteins such as CROCC (Rootletin). Collectively, these findings uncover previously unrecognized roles for YAP1 in adult spinal cord stem-cell fate decisions and provide a molecular framework for leveraging these cells in regenerative strategies targeting spinal cord repair.

cell biology↗

bioRxiv2024

NEUROG2 regulates a human-specific neurodevelopmental gene regulatory program

Unique hallmarks of human neocortical development include slower rates of neurogenesis and the establishment of an extracellular matrix-rich, outer-subventricular zone that supports basal neural progenitor cell expansion. How gene regulatory networks have evolved to support these human-specific neurodevelopmental features is poorly understood. Mining single cell data from cerebral organoids and human fetal cortices, we found that NEUROG2 expression is enriched in basal neural progenitor cells. To identify and purify NEUROG2-expressing cells and trace their short-term lineage, we engineered two NEUROG2-mCherry knock-in human embryonic stem cell lines to produce cerebral organoids. Transcriptomic profiling of mCherry-high organoid cells revealed elevated expression of PPP1R17, associated with a fast-evolving human-accelerated regulatory region, oligodendrocyte precursor cell and extracellular matrix-associated gene transcripts. Conversely, only neurogenic gene transcripts were enriched in mCherry-high cortical cells from Neurog2:mCherry knock-in mice. Finally, we show that Neurog2 is sufficient to induce Ppp1r17, which slows human neural progenitor cell division, and Col13a1, an extracellular matrix gene, in P19 cells. NEUROG2 thus regulates a human neurodevelopmental gene regulatory program implicated in supporting a pro-proliferative basal progenitor cell niche and tempering the neurogenic pace. SUMMARY STATEMENTTranscriptomic analyses of NEUROG2-mCherry knock-in human embryonic stem cell-derived cerebral organoids reveal a link between NEUROG2 and extracellular matrix remodeling during human cortical development.

developmental biology↗

bioRxiv2023

Proneural genes form a combinatorial code to diversify neocortical neural progenitor cells

Neocortical neural progenitor cells (NPCs) are molecularly heterogeneous, yet the genes that confer distinct neuronal morphologies and connectivities during development are poorly understood. Here, we determined that a proneural gene combinatorial code diversifies cortical NPCs. By mining scRNA-seq data from murine embryonic and early postnatal cortices and generating trajectory inference models, we found that Neurog2 is predominant, and is transiently co-expressed with Ascl1 and/or Neurog1 during an apical-to-basal NPC transition state in NPCs with early pseudotime identities. To assess whether proneural gene pairs confer distinct properties, we first used Neurog2/Ascl1 reporter mice expressing unique reporters, revealing that NPCs have distinct cell division modes and cell cycle dynamics dependent on their proneural gene profile. To assess Neurog2/Neurog1 interactions, we used double knock-out mice and novel split-Cre transgenics crossed to a Rosa-diptheria-toxin-A line to delete double+ cells, showing Neurog1/Neurog2 are specifically required to generate early-born neurons and to maintain NPCs. Finally, in silico mutation of a cortical Neurog2-gene regulatory network and validation using Neurog1/Neurog2 mutant and deleter mice, identified Bclllb and Nhlh2, expressed in early-born neurons, as dependent on Neurog1/Neurog2. Our data explains how proneural genes act combinatorically to diversify gene regulatory networks, thereby lineage restricting NPCs and creating cortical neuronal diversity.

developmental biology↗

bioRxiv2021

Reaction of ependymal cells to spinal cord injury: a potential role for oncostatin pathway and microglial cells

Ependymal cells with stem cell properties reside in the adult spinal cord around the central canal. They rapidly activate and proliferate after spinal cord injury, constituting a source of new cells. They produce neurons and glial cells in lower vertebrates but they mainly generate glial cells in mammals. The mechanisms underlying their activation and their glial-biased differentiation in mammals remain ill-defined. This represents an obstacle to control these cells. We addressed this issue using RNA profiling of ependymal cells before and after injury. We found that these cells activate STAT3 and ERK/MAPK signaling during injury and downregulate cilia-associated genes and FOXJ1, a central transcription factor in ciliogenesis. Conversely, they upregulate 510 genes, six of them more than 20 fold, namely Crym, Ecm1, Ifi202b, Nupr1, Rbp1, Thbs2 and Osmr. OSMR is the receptor for the inflammatory cytokine oncostatin (OSM) and we studied its regulation and role using neurospheres derived from ependymal cells. We found that OSM induces strong OSMR and p-STAT3 expression together with proliferation reduction and astrocytic differentiation. Conversely, production of oligodendrocyte-lineage OLIG1+ cells was reduced. OSM is specifically expressed by microglial cells and was strongly upregulated after injury. We observed microglial cells apposed to ependymal cells in vivo and co-cultures experiments showed that these cells upregulate OSMR in neurosphere cells. Collectively, these results support the notion that microglial cells and OSMR/OSM pathway regulate ependymal cells in injury. In addition, the generated high throughput data provides a unique molecular resource to study how ependymal cell react to spinal cord lesion.

cell biology↗