Biology subjects

Joyner, A. L.

Publications and source records attributed to Joyner, A. L..

At least 19 recordsLinked to original sources

bioRxiv2026

A Rare Nestin-Expressing Granule Cell Precursor Subpopulation Underlies SHH Medulloblastoma Formation

Granule cell precursors (GCPs) drive the major postnatal expansion of the cerebellum and are the cells of origin of sonic hedgehog medulloblastoma (SHH MB). Although GCPs are often treated as a uniform population, increasing evidence suggests they are heterogeneous, and whether specific subpopulations show distinct tumorigenic competence remains unclear. Here, we identified a rare Nestin-expressing GCP subpopulation in the normal early postnatal cerebellum and showed that it is spatially restricted, molecularly distinct and highly competent to form tumors. These cells are enriched in the posterior external granule layer and co-express Atoh1. Using different SHH MB mouse models, we showed that when this rare subpopulation of GCPs is targeted they can give rise to SHH MB with an efficiency comparable to targeting a larger number of Atoh1-expressing GCPs and that tumors derived from Nestin-expressing GCPs arise in the posterior-lateral cerebellum. Single cell RNA sequencing revealed that Nestin-expressing GCP have a transcriptome indicating reduced neuronal differentiation and enrichment for stem cell genes compared to bulk GCPs and more closely align with SHH MB cells. Together, our findings reveal functionally important heterogeneity within the GCP lineage and suggest that SHH MB arises preferentially from a small subpopulation of GCPs that express Nestin.

cancer biology↗

bioRxiv2025

Dose-dependent NFI regulation of progenitor lifespan and output underlying human neocortical malformation

Nuclear Factor I (NFI) misexpressions in humans are associated with severe brain malformations, yet the underlying mechanisms remain poorly understood. Here we show that NFIs regulate the broad lineage progression and lifespan of radial glial progenitors (RGPs), and consequently neocortical development in a dose-dependent manner. Human cerebral organoids carrying patient-mimicking NFI mutations exhibit expression level-dependent bidirectional impairments in RGP temporal development, coinciding with patient phenotypes. In mouse models, selective removal of NFIs leads to a dramatic protraction of RGP lineage progression and lifespan, excessive progeny output, and neocortical overgrowth and abnormal folding, whereas overexpression of NFIs accelerates RGP lineage progression, resulting in developmental stage-dependent precocious productions of diverse neural progenies. Moreover, NFIs exhibit a positive auto-regulation and progressive increase in expression, and regulate distinct temporal-specific targets underlying RGP lineage progression. These results suggest that NFIs act as evolutionarily conserved key global temporal regulators of RGP lineage progression and neocortical development. HIGHLIGHTSO_LINFIs affect human RGP temporal development coinciding with patient phenotypes. C_LIO_LINFI removal protracts RGP lineage progression and lifespan with excessive progeny output. C_LIO_LINFI overexpression accelerates RGP lineage progression with precocious progeny output. C_LIO_LINFIs regulate distinct temporal-specific targets underlying RGP lineage progression. C_LI

neuroscience↗

bioRxiv2025

The regenerative potential of adult Nestin+ cerebellar astroglia is limited compared to in neonates

There is a crucial need for strategies that stimulate repair in the adult brain. The neonatal mouse cerebellum can regenerate via the adaptive reprogramming of nestin (Nes)-expressing progenitors (NEPs). However, analysis of Nes+ cells of the adult cerebellum is limited. Using reporter lines and genetic inducible fate mapping, we show that adult Nes+ cells are mainly Bergmann glia (Nes+ Bg) that have in vitro sphere-forming ability. Following injury, Nes+ Bg increase in number due to upregulation of Nes in Hopx-expressing Bg, but the cells exhibit limited regeneration. ATAC-seq of Nes+ Bg reveals that silencing of developmental genes compared to neonatal NEPs contributes to the impaired regeneration. Activating sonic hedgehog signalling augments the number of Nes+ Bg after injury but not neurogenesis, showing additional cues are required. Our results demonstrate an age-dependent decline in the regenerative potential of NEPs and highlight Nes+ Bg as potential injury-responsive cells that could facilitate regeneration.

developmental biology↗

bioRxiv2025

PTEN restrains SHH medulloblastma growth through cell autonomous and nonautonomous mechanisms

A third of patients with the pediatric cerebellar tumor Medulloblastoma (MB) have mutations that activate Sonic hedgehog (SHH) signaling (SHH-MB subgroup). The contribution of secondary mutations to tumor severity, however is not clear. PTEN mutations are enriched in the SHH-1 subtype that has the lowest survival rate. Widespread heterozygous loss of Pten in two SHH-MB mouse models increases penetrance and excellerates onset of differentiated tumors. We delineated cellular and transcriptional changes that accelerate tumor growth and cause differentiation using a sporadic SHH-MB mouse model expressing oncogenic SmoM2 in rare cerebellar granule cell precursors (GCPs) and scRNA-seq analysis. Homozygous but not heterozygous sporadic loss of Pten resulted in rapid acceleration of tumor growth and end stage disease by 40 days, compared to [~]25% survival in control SmoM2 mice at 100 days. Heterozygous PTEN mutations therefore should negatively impact disease outcome primarily with germline mutations. Loss of Pten in normal or SmoM2-expressing GCPs increased proliferation and enhanced progenitor state initially but by 12 days Pten mutant SmoM2 tumors were highly differentiated due to increased survival of non-proliferating GCPs. Furthermore, macrophage infiltration and cytotoxicity appeared reduced in differentiated regions of tumors lacking Pten, indicating cell nonautonomous changes could also contribute to accelerated tumor growth.

cancer biology↗

bioRxiv2025

Transcription factors SP5 and SP8 drive primary cilia formation

While specific transcription factors are known to regulate cell fate decisions, the degree to which they can stimulate formation of specific cell organelles is less clear. We used a multi-omics comparison of the transcriptomes of ciliated and non-ciliated embryonic cells to identify transcription factors upregulated in ciliated cells, and conditional genetics in mouse embryos and stem cells to demonstrate that SP5/8 regulate cilia formation and gene expression. In Sp5/8 mutant embryos primary and motile cilia are shorter than normal and reduced in number across cell types, contributing to situs inversus and hydrocephalus. Moreover, expression of SP8 is sufficient to induce primary cilia in unciliated cells. This work opens new avenues for studying cilia assembly using stem cell models and offers new insights into human ciliopathies.

developmental biology↗

bioRxiv2024

An increase in reactive oxygen species underlies neonatal cerebellum repair

The neonatal mouse cerebellum shows remarkable regenerative potential upon injury at birth, wherein a subset of Nestin-expressing progenitors (NEPs) undergoes adaptive reprogramming to replenish granule cell progenitors that die. Here, we investigate how the microenvironment of the injured cerebellum changes upon injury and contributes to the regenerative potential of normally gliogenic-NEPs and their adaptive reprogramming. Single cell transcriptomic and bulk chromatin accessibility analyses of the NEPs from injured neonatal cerebella compared to controls show a temporary increase in cellular processes involved in responding to reactive oxygen species (ROS), a known damage-associated molecular pattern. Analysis of ROS levels in cerebellar tissue confirm a transient increased one day after injury at postanal day 1, overlapping with the peak cell death in the cerebellum. In a transgenic mouse line that ubiquitously overexpresses human mitochondrial catalase (mCAT), ROS is reduced 1 day after injury to the granule cell progenitors, and we demonstrate that several steps in the regenerative process of NEPs are curtailed leading to reduced cerebellar growth. We also provide preliminary evidence that microglia are involved in one step of adaptive reprogramming by regulating NEP replenishment of the granule cell precursors. Collectively, our results highlight that changes in the tissue microenvironment regulate multiple steps in adaptative reprogramming of NEPs upon death of cerebellar granule cell progenitors at birth, highlighting the instructive roles of microenvironmental signals during regeneration of the neonatal brain.

developmental biology↗

bioRxiv2024

Cerebellar output neurons impair non-motor behaviors by altering development of extracerebellar connectivity

The capacity of the brain to compensate for insults during development depends on the type of cell loss, whereas the consequences of genetic mutations in the same neurons are difficult to predict. We reveal powerful compensation from outside the cerebellum when the excitatory cerebellar output neurons are ablated embryonically and demonstrate that the minimum requirement for these neurons is for motor coordination and not learning and social behaviors. In contrast, loss of the homeobox transcription factors Engrailed1/2 (EN1/2) in the cerebellar excitatory lineage leads to additional deficits in adult learning and spatial working memory, despite half of the excitatory output neurons being intact. Diffusion MRI indicates increased thalamo-cortico-striatal connectivity in En1/2 mutants, showing that the remaining excitatory neurons lacking En1/2 exert adverse effects on extracerebellar circuits regulating motor learning and select non-motor behaviors. Thus, an absence of cerebellar output neurons is less disruptive than having cerebellar genetic mutations.

neuroscience↗

bioRxiv2023

Engrailed transcription factors direct excitatory cerebellar neuron diversity and survival

The excitatory neurons of the three cerebellar nuclei (eCN) form the primary output for the cerebellar circuit. The medial eCN (eCNm) were recently divided into molecularly defined subdomains in the adult, however how they are established during development is not known. We define molecular subdomains of the eCNm using scRNA-seq and spatial expression analysis and show they evolve during embryogenesis to resemble the adult. Furthermore, the eCNm is transcriptionally divergent from the rest of the eCN by E14.5. We previously showed that loss of the homeobox genes En1 and En2 leads to death of a subset of embryonic eCNm. We demonstrate that mutation of En1/2 in embryonic eCNm results in cell death of specific posterior eCNm molecular subdomains and loss of TBR2 (EOMES) expression in an anterior subdomain, as well as reduced synaptic gene expression. We further reveal a similar function for EN1/2 in mediating TBR2 expression, neuron differentiation and survival in the two other cerebellar excitatory neuron types. Thus, our work defines embryonic eCNm molecular diversity and reveals conserved roles for EN1/2 in the cerebellar excitatory neuron lineage.

developmental biology↗

bioRxiv2023

Cell division angle regulates the tissue mechanics and tunes the amount of cerebellar folding

Modeling has proposed that the amount of neural tissue folding is set by the level of differential-expansion between tissue layers and that the wavelength is set by the thickness of the outer layer. Here we used inbred mouse strains with distinct amounts of cerebellar folding to investigate these predictions. We identified a critical period where the folding amount diverges between the strains. In this period, regional changes in the level of differential-expansion between the external granule layer (EGL) and underlying core correlate with the folding amount in each strain. Additionally, the thickness of the EGL is regionally adjusted during the critical period alongside corresponding changes in wavelength. While the number of SHH-expressing Purkinje cells predicts the folding amount, the proliferation rate in the EGL is the same between the strains. However, regional changes in the cell division angle within the EGL predicts both the tangential-expansion and thickness of the EGL. Cell division angle is likely a tunable mechanism whereby both the level of differential-expansion and thickness of the EGL are regionally tuned to set the amount and wavelength of folding.

developmental biology↗

bioRxiv2022

Childhood cancer mutagenesis caused by a domesticated DNA transposase

Genomic rearrangements are a hallmark of most solid tumors, including medulloblastoma, one of the most common brain tumors in children. Childhood cancers involve dysregulated cell development, but their mutational causes remain largely unknown. One of the most common forms of medulloblastoma is caused by ectopic activation of Sonic Hedgehog (SHH) signaling in cerebellar granule cell progenitors, associated with genetic deletions, amplifications, and other oncogenic chromosomal rearrangements. Here, we show that PiggyBac Transposable Element Derived 5 (Pgbd5) promotes tumor development in multiple developmentally-accurate mouse models of SHH medulloblastoma. Most mice with Pgbd5 deficiency do not develop tumors, while Pgbd5-deficient mice maintain largely normal cerebellar development. Mouse medulloblastomas expressing Pgbd5 exhibit significantly increased numbers of somatic structural DNA rearrangements, with PGBD5-specific transposon sequences at their breakpoints. Similar sequence breakpoints recurrently affect somatic DNA rearrangements of known tumor suppressors and oncogenes in medulloblastomas in 329 children. Therefore, this study identifies PGBD5 as a primary medulloblastoma mutator and provides a genetic mechanism responsible for the generation of somatic oncogenic DNA rearrangements in childhood cancer. One-Sentence SummaryInduction of somatic oncogenic mutations by the DNA transposase PGBD5 in cerebellar progenitor cells promotes medulloblastoma development.

cancer biology↗

bioRxiv2020

ASCL1 drives induction of a transitory cell state required for repair of the injured neonatal brain

The underlying molecular foundation of neural progenitor diversity and plasticity is critical for understanding repair processes. The neonatal cerebellum with multiple progenitor populations has high regenerative potential. Upon ablation of cerebellar granule cell progenitors at birth, a normally gliogenic Nestin-expressing progenitor (NEP) in the Bergmann glia (Bg) layer (BgL-NEPs) undergoes adaptive reprograming to restore granule neuron production while a white matter NEP (WM-NEPs) reduces interneuron production. However, the cellular states and genes regulating the NEP fate switch are not known. Here using scRNA-seq and fate-mapping, we defined the molecular subtypes of NEPs and their lineages under homeostasis and repair. Five NEP populations comprising two molecular subtypes, Hopx-expressing gliogenic- and Ascl1-expressing neurogenic-NEPs were identified in both states. Furthermore, in the WM, distinct NEP populations generate interneurons or astrocytes, and amongst gliogenic-NEPs, astrocyte and Bg lineages are molecularly separable. Importantly, we uncovered that after injury a new transitory cellular state arises from Hopx-NEPs in the BgL that is defined by initiation of expression of the neurogenic gene Ascl1. Moreover, Ascl1 is required for adaptive reprogramming and the full regenerative capacity of the cerebellum. We thus define new populations of NEPs and identifed the transcription factor responsible for inducing a transitory cell critical for a glial to neural switch in vivo following injury.

developmental biology↗

bioRxiv2019

Single-cell profiling and SCOPE-seq reveal the lineage dynamics of adult neurogenesis and NOTUM as a key V-SVZ regulator

Neural stem cells (NSCs) and their progeny reside in specialized niches in the adult mammalian brain where they generate new neurons and glia throughout life. Adult NSCs of the ventricular-subventricular zone (V-SVZ) are prone to rapid exhaustion; thus timely, context-dependent neurogenesis demands adaptive signaling among the vast number of neighboring progenitors nestled between the ventricular surface and nearby blood vessels. To dissect adult neuronal lineage progression and regulation, we profiled >56,000 V-SVZ and olfactory bulb (OB) cells by single-cell RNA-sequencing (scRNA-seq). Our analyses revealed the diversity of V-SVZ-derived OB neurons, the temporal dynamics of lineage progression, and a key intermediate NSC population enriched for expression of Notum, which encodes a secreted WNT antagonist. Single Cell Optical Phenotyping and Expression (SCOPE-seq), a technology linking live cell imaging with scRNA-seq, uncovered dynamic control of cell size concomitant with NSC differentiation with Notum+ NSCs at a critical size poised for cell division, and a preference of NOTUM surface binding to neuronal precursors with active WNT signaling. Finally, in vivo pharmacological inhibition of NOTUM significantly expanded neuronal precursor pools in the V-SVZ. Our findings highlight a critical regulatory state during NSC activation marked by NOTUM, a secreted enzyme that ensures efficient neurogenesis by preventing WNT signaling activation in NSC progeny.

neuroscience↗

bioRxiv2019

A bestiary of genetic mouse lines and related tools for inducible and reversible intersectional misexpression

Thanks to many advances in genetic manipulation, mouse models have become very powerful in their ability to interrogate biological processes. In order to precisely target expression of a gene of interest to particular cell types, intersectional genetic approaches utilizing two promoter/enhancers unique to a cell type are ideal. Within these methodologies, variants that add temporal control of gene expression are the most powerful. We describe the development, validation and application of an intersectional approach that involves three transgenes, requiring the intersection of two promoter/enhancers to target gene expression to precise cell types. Furthermore, the approach utilizes available lines expressing tTA/rTA to control timing of gene expression based on whether doxycycline is absent or present, respectively. We also show that the approach can be extended to other animal models, using chicken embryos. We generated three mouse lines targeted at the Tigre (Igs7) locus with TRE-loxP-tdTomato-loxP upstream of three genes (p21, DTA and Ctgf) and combined them with Cre and tTA/rtTA lines that target expression to the cerebellum and limbs. Our tools will facilitate unraveling biological questions in multiple fields and organisms. Summary statementAhmadzadeh et al. present a collection of four mouse lines and genetic tools for misexpression-mediated manipulation of cellular activity with high spatiotemporal control, in a reversible manner.

molecular biology↗

bioRxiv2019

Disruption of the CSF-1-CSF-1R axis alters cerebellar microglia and is associated with motor and social interaction defects

Microglia, the brain resident macrophages, critically shape forebrain neuronal circuits. However, their precise function in the cerebellum is unknown. Here we show that human and mouse cerebellar microglia express a unique molecular program distinct from forebrain microglia. Cerebellar microglial identity was driven by the CSF-1R ligand CSF-1, independently of the alternate CSF-1R ligand, IL-34. Accordingly, CSF-1 depletion from Nestin+ cells led to severe depletion and transcriptional alterations of cerebellar microglia, while microglia in the forebrain remained intact. Strikingly, CSF-1 deficiency and alteration of cerebellar microglia were associated with reduced Purkinje cells, altered neuronal function, and defects in motor learning and social novelty interactions. These findings reveal a novel CSF-1-CSF-1R signaling-mediated mechanism that contributes to motor function and social behavior.\n\nSummaryMicroglia are a heterogeneous population whose identity and function are dictated by signals from their microenvironment. Kana et al. show that CSF-1 signaling is critical for maintaining cerebellar microglial transcriptional identity and homeostasis, and that altering the CSF-1 - CSF-1R axis leads to motor and behavioral defects.

neuroscience↗

bioRxiv2019

YAP is involved in replenishment of granule cell progenitors following injury to the neonatal cerebellum

The cerebellum (CB) undergoes major rapid growth during the third trimester and early neonatal stage in humans, making it vulnerable to injuries in pre-term babies. Experiments in mice have revealed a remarkable ability of the neonatal CB to recover from injuries around birth. In particular, recovery following irradiation-induced ablation of granule cell precursors (GCPs) involves adaptive reprogramming of Nestin-expressing glial progenitors (NEPs). Sonic hedgehog signaling is required for the initial step in NEP reprogramming; however, the full spectrum of developmental signaling pathways that promote NEP-driven regeneration is not known. Since the growth regulatory Hippo pathway has been implicated in the repair of several tissue types, we tested whether Hippo signaling is involved in regeneration of the CB. Using mouse models, we found that the Hippo pathway transcriptional co-activator YAP (Yes-associated protein) but not TAZ (transcriptional coactivator with PDZ binding motif) is required in NEPs for full recovery of the CB following irradiation one day after birth. The size of the adult CB, and in particular the internal granule cell layer produced by GCPs, is significantly reduced in mutants, and the organization of Purkinje cells and Bergmann glial fibers is disrupted. Surprisingly, the initial proliferative response of Yap mutant NEPs to irradiation is normal and the cells migrate to the GCP niche, but then undergo increased cell death. Loss of Yap in NEPs or GCPs during normal development leads to only mild defects in differentiation. Moreover, loss of Taz does not abrogate regeneration of GCPs by Yap mutant NEPs or alter development of the cerebellum. Our study provides new insights into the molecular signaling underlying postnatal cerebellar development and regeneration.

developmental biology↗

bioRxiv2018

Genetic deletion of genes in the cerebellar rhombic lip lineage can stimulate compensation through adaptive reprogramming of ventricular zone-derived progenitors

BackgroundThe cerebellum is a foliated posterior brain structure involved in coordination of motor movements and cognition. The cerebellum undergoes rapid growth postnataly due to Sonic Hedgehog (SHH) signaling-dependent proliferation of ATOH1+ granule cell precursors (GCPs) in the external granule cell layer (EGL), a key step for generating cerebellar foliation and the correct number of granule cells. Due to its late development, the cerebellum is particularly vulnerable to injury from preterm birth and stress around birth. We recently uncovered an intrinsic capacity of the developing cerebellum to replenish ablated GCPs via adaptive reprogramming of Nestin-expressing progenitors (NEPs). However, whether this compensation mechanism occurs in mouse mutants affecting the developing cerebellum and could lead to mis-interpretation of phenotypes was not known.\n\nMethodsWe used two different approaches to remove the main SHH signaling activator GLI2 in GCPs: 1) our mosaic mutant analysis with spatial and temporal control of recombination (MASTR) technique to delete Gli2 in a small subset of GCPs; 2) An Atohl-Cre transgene to delete Gli2 in most of the EGL. Genetic Inducible Fate Mapping (GIFM) and live imaging were used to analyze the behavior of NEPs after Gli2 deletion.\n\nResultsMosaic analysis demonstrated that SHH-GLI2 signaling is critical for generating the correct pool of granule cells by maintaining GCPs in an undifferentiated proliferative state and promoting their survival. Despite this, inactivation of GLI2 in a large proportion of GCPs in the embryo did not lead to the expected dramatic reduction in the size of the adult cerebellum. GIFM uncovered that NEPs do indeed replenish GCPs in Gli2 conditional mutants, and then expand and partially restore the production of granule cells. Furthermore, the SHH signaling-dependent NEP compensation requires Gli2, demonstrating that the activator side of the pathway is involved.\n\nConclusionWe demonstrate that a mouse conditional mutation that results in loss of SHH signaling in GCPs is not sufficient to induce long term severe cerebellum hypoplasia. The ability of the neonatal cerebellum to regenerate after loss of cells via a response by NEPs must therefore be considered when interpreting the phenotypes of conditional mutants affecting GCPs.

developmental biology↗

bioRxiv2018

Brain folding is initiated by mechanical constraints without a cellular pre-pattern

During human brain development the cerebellum and cerebral cortex fold into robust patterns that increase and compartmentalize neural circuits. Although differential expansion of elastic materials has been proposed to explain brain folding, the cellular and physical processes responsible at the time of folding have not been defined. Here we used the murine cerebellum, with 8-10 folds, as a tractable model to study brain folding. At folding initiation we considered the cerebellum as a bilayer system with a fluidlike outer layer of proliferating precursors and an incompressible core. We discovered that there is no obvious cellular pre-pattern for folding, since when folding initiates, the precursors within the outer layer have uniform sizes, shapes and proliferation, as well as a distribution of glial fibers. Furthermore, although differential expansion is created by the outer layer expanding faster than the core at folding initiation, thickness variations arise in the outer layer that are inconsistent with elastic material models. A multiphase model was applied that includes radial and circumferential tension and mechanical constraints derived from in vivo measurements. Our results demonstrate that cerebellar folding emerges from mechanical forces generated by uniform cell behaviors. We discuss how our findings apply to human cerebral cortex folding.

developmental biology↗

bioRxiv2018

Cerebellar nuclei neurons dictate growth of the cortex through developmental scaling of presynaptic Purkinje cells

Efficient function of neural systems requires the production of specific cell types in the correct proportions. Here we report that reduction of the earliest born neurons of the cerebellum, excitatory cerebellar nuclei neurons (eCN), results in a subsequent reduction in growth of the cerebellar cortex due to an accompanying loss of their presynaptic target Purkinje cells. Conditional knockout of the homeobox genes En1 and En2 (En1/2) in the rhombic lip-derived eCN and granule cell precursors leads to embryonic loss of a subset of medial eCN and cell non-autonomous and location specific loss of Purkinje cells, with subsequent proportional scaling down of cortex growth. We propose that subsets of eCN dictate the survival of their specific Purkinje cell partners, and in turn sonic hedgehog secreted by Purkinje cells scales the expansion of granule cells and interneurons to produce functional local circuits and the proper folded morphology of the cerebellum.

developmental biology↗