RESUMO
The neocortex consists of a vast number of diverse neurons that form distinct layers and intricate circuits at the single-cell resolution to support complex brain functions1. Diverse cell-surface molecules are thought to be key for defining neuronal identity, and they mediate interneuronal interactions for structural and functional organization2-6. However, the precise mechanisms that control the fine neuronal organization of the neocortex remain largely unclear. Here, by integrating in-depth single-cell RNA-sequencing analysis, progenitor lineage labelling and mosaic functional analysis, we report that the diverse yet patterned expression of clustered protocadherins (cPCDHs)-the largest subgroup of the cadherin superfamily of cell-adhesion molecules7-regulates the precise spatial arrangement and synaptic connectivity of excitatory neurons in the mouse neocortex. The expression of cPcdh genes in individual neocortical excitatory neurons is diverse yet exhibits distinct composition patterns linked to their developmental origin and spatial positioning. A reduction in functional cPCDH expression causes a lateral clustering of clonally related excitatory neurons originating from the same neural progenitor and a significant increase in synaptic connectivity. By contrast, overexpression of a single cPCDH isoform leads to a lateral dispersion of clonally related excitatory neurons and a considerable decrease in synaptic connectivity. These results suggest that patterned cPCDH expression biases fine spatial and functional organization of individual neocortical excitatory neurons in the mammalian brain.
Assuntos
Regulação da Expressão Gênica , Neocórtex , Protocaderinas , Animais , Camundongos , Interneurônios/metabolismo , Neocórtex/anatomia & histologia , Neocórtex/citologia , Neocórtex/metabolismo , Neurônios/metabolismo , Protocaderinas/genética , Protocaderinas/metabolismo , Sinapses/metabolismo , Transmissão SinápticaRESUMO
The neurons of the three cerebellar nuclei (CN) are the primary output neurons of the cerebellum. The excitatory neurons (e) of the medial (m) CN (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 mouse embryonic eCNm using single-cell RNA-sequencing and spatial expression analysis, showing that they evolve during embryogenesis to prefigure the adult. Furthermore, eCNm are transcriptionally divergent from cells in the other nuclei by embryonic day 14.5. We previously showed that loss of the homeobox genes En1 and En2 leads to loss of approximately half of the embryonic eCNm. We demonstrate that mutation of En1/2 in the embryonic eCNm results in death of specific posterior eCNm molecular subdomains and downregulation of TBR2 (EOMES) in an anterior embryonic 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 other excitatory neurons (granule and unipolar brush cells). Thus, our work defines embryonic eCNm molecular diversity and reveals conserved roles for EN1/2 in the cerebellar excitatory neuron lineage.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio , Neurônios , Animais , Proteínas de Homeodomínio/metabolismo , Proteínas de Homeodomínio/genética , Camundongos , Neurônios/metabolismo , Neurônios/citologia , Sobrevivência Celular/genética , Diferenciação Celular/genética , Cerebelo/embriologia , Cerebelo/metabolismo , Cerebelo/citologia , Proteínas com Domínio T/metabolismo , Proteínas com Domínio T/genética , Núcleos Cerebelares/metabolismo , Núcleos Cerebelares/embriologia , Núcleos Cerebelares/citologia , Análise de Célula Única , Proteínas do Tecido NervosoRESUMO
Modeling has led to proposals 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 distinct critical period during which the folding amount diverges between the two 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 varies regionally during the critical period alongside corresponding changes in wavelength. The number of SHH-expressing Purkinje cells predicts the folding amount, but 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 the thickness of the EGL. Cell division angle is likely a tunable mechanism whereby both the level of differential expansion along the perimeter and the thickness of the EGL are regionally tuned to set the amount and wavelength of folding.
Assuntos
Cerebelo , Células de Purkinje , Camundongos , Animais , Divisão CelularRESUMO
Radial glial progenitor cells (RGPs) are the major neural progenitor cells that generate neurons and glia in the developing mammalian cerebral cortex1-4. In RGPs, the centrosome is positioned away from the nucleus at the apical surface of the ventricular zone of the cerebral cortex5-8. However, the molecular basis and precise function of this distinctive subcellular organization of the centrosome are largely unknown. Here we show in mice that anchoring of the centrosome to the apical membrane controls the mechanical properties of cortical RGPs, and consequently their mitotic behaviour and the size and formation of the cortex. The mother centriole in RGPs develops distal appendages that anchor it to the apical membrane. Selective removal of centrosomal protein 83 (CEP83) eliminates these distal appendages and disrupts the anchorage of the centrosome to the apical membrane, resulting in the disorganization of microtubules and stretching and stiffening of the apical membrane. The elimination of CEP83 also activates the mechanically sensitive yes-associated protein (YAP) and promotes the excessive proliferation of RGPs, together with a subsequent overproduction of intermediate progenitor cells, which leads to the formation of an enlarged cortex with abnormal folding. Simultaneous elimination of YAP suppresses the cortical enlargement and folding that is induced by the removal of CEP83. Together, these results indicate a previously unknown role of the centrosome in regulating the mechanical features of neural progenitor cells and the size and configuration of the mammalian cerebral cortex.
Assuntos
Centrossomo/metabolismo , Córtex Cerebral/citologia , Córtex Cerebral/embriologia , Células Ependimogliais/citologia , Células-Tronco Neurais/citologia , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Proteínas de Ciclo Celular/metabolismo , Membrana Celular/metabolismo , Membrana Celular/patologia , Proliferação de Células , Centríolos/metabolismo , Córtex Cerebral/patologia , Feminino , Masculino , Camundongos , Proteínas Associadas aos Microtúbulos/deficiência , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Microtúbulos/metabolismo , Microtúbulos/patologia , Neurogênese , Proteínas de Sinalização YAPRESUMO
The cerebellum has a simple cytoarchitecture consisting of a folded cortex with three cell layers that surrounds a nuclear structure housing the output neurons. The excitatory neurons are generated from a unique progenitor zone, the rhombic lip, whereas the inhibitory neurons and astrocytes are generated from the ventricular zone. The growth phase of the cerebellum is driven by lineage-restricted progenitor populations derived from each zone. Research during the past decade has uncovered the importance of cell-to-cell communication between the lineages through largely unknown signaling mechanisms for regulating the scaling of cell numbers and cell plasticity during mouse development and following injury in the neonatal (P0-P14) cerebellum. This Review focuses on how the interplay between cell types is key to morphogenesis, production of robust neural circuits and replenishment of cells after injury, and ends with a discussion of the implications of the greater complexity of the human cerebellar progenitor zones for development and disease.
Assuntos
Cerebelo , Neurônios , Animais , Astrócitos , Humanos , Camundongos , Morfogênese , Neurônios/metabolismo , Células de PurkinjeRESUMO
Study of the origin and development of cerebellar tumours has been hampered by the complexity and heterogeneity of cerebellar cells that change over the course of development. Here we use single-cell transcriptomics to study more than 60,000 cells from the developing mouse cerebellum and show that different molecular subgroups of childhood cerebellar tumours mirror the transcription of cells from distinct, temporally restricted cerebellar lineages. The Sonic Hedgehog medulloblastoma subgroup transcriptionally mirrors the granule cell hierarchy as expected, while group 3 medulloblastoma resembles Nestin+ stem cells, group 4 medulloblastoma resembles unipolar brush cells, and PFA/PFB ependymoma and cerebellar pilocytic astrocytoma resemble the prenatal gliogenic progenitor cells. Furthermore, single-cell transcriptomics of human childhood cerebellar tumours demonstrates that many bulk tumours contain a mixed population of cells with divergent differentiation. Our data highlight cerebellar tumours as a disorder of early brain development and provide a proximate explanation for the peak incidence of cerebellar tumours in early childhood.
Assuntos
Neoplasias Cerebelares/genética , Neoplasias Cerebelares/patologia , Evolução Molecular , Feto/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Regulação Neoplásica da Expressão Gênica , Transcrição Gênica , Animais , Neoplasias Cerebelares/classificação , Cerebelo/citologia , Cerebelo/embriologia , Cerebelo/metabolismo , Criança , Feminino , Feto/citologia , Glioma/classificação , Glioma/genética , Glioma/patologia , Humanos , Meduloblastoma/classificação , Meduloblastoma/genética , Meduloblastoma/patologia , Camundongos , Análise de Sequência de RNA , Análise de Célula Única , Fatores de Tempo , Transcriptoma/genéticaRESUMO
Magnetic Resonance Imaging (MRI) resolution continues to improve, making it important to understand the cellular basis for different MRI contrast mechanisms. Manganese-enhanced MRI (MEMRI) produces layer-specific contrast throughout the brain enabling in vivo visualization of cellular cytoarchitecture, particularly in the cerebellum. Due to the unique geometry of the cerebellum, especially near the midline, 2D MEMRI images can be acquired from a relatively thick slice by averaging through areas of uniform morphology and cytoarchitecture to produce very high-resolution visualization of sagittal planes. In such images, MEMRI hyperintensity is uniform in thickness throughout the anterior-posterior axis of sagittal sections and is centrally located in the cerebellar cortex. These signal features suggested that the Purkinje cell layer, which houses the cell bodies of the Purkinje cells and the Bergmann glia, is the source of hyperintensity. Despite this circumstantial evidence, the cellular source of MRI contrast has been difficult to define. In this study, we quantified the effects of selective ablation of Purkinje cells or Bergmann glia on cerebellar MEMRI signal to determine whether signal could be assigned to one cell type. We found that the Purkinje cells, not the Bergmann glia, are the primary of source of the enhancement in the Purkinje cell layer. This cell-ablation strategy should be useful for determining the cell specificity of other MRI contrast mechanisms.
Assuntos
Cerebelo , Manganês , Humanos , Manganês/metabolismo , Cerebelo/patologia , Células de Purkinje/metabolismo , Células de Purkinje/patologia , Neuroglia/metabolismo , Imageamento por Ressonância Magnética/métodosRESUMO
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 using 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 uses available lines expressing tTA/rTA to control the 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.
Assuntos
Modelos Animais de Doenças , Regulação da Expressão Gênica/efeitos dos fármacos , Expressão Gênica/efeitos dos fármacos , Técnicas de Transferência de Genes , Transgenes , Animais , Cerebelo , Embrião de Galinha , Doxiciclina/farmacologia , Extremidades , Feminino , Masculino , Camundongos , Camundongos Transgênicos , Regiões Promotoras Genéticas , Transativadores/genética , Transcrição GênicaRESUMO
Catch-up growth after insults to growing organs is paramount to achieving robust body proportions. In fly larvae, injury to individual tissues is followed by local and systemic compensatory mechanisms that allow the damaged tissue to regain normal proportions with other tissues. In vertebrates, local catch-up growth has been described after transient reduction of bone growth, but the underlying cellular responses are controversial. We developed an approach to study catch-up growth in foetal mice in which mosaic expression of the cell cycle suppressor p21 is induced in the cartilage cells (chondrocytes) that drive long-bone elongation. By specifically targeting p21 expression to left hindlimb chondrocytes, the right limb serves as an internal control. Unexpectedly, left-right limb symmetry remained normal, revealing deployment of compensatory mechanisms. Above a certain threshold of insult, an orchestrated response was triggered involving local enhancement of bone growth and systemic growth reduction that ensured that body proportions were maintained. The local response entailed hyperproliferation of spared left limb chondrocytes that was associated with reduced chondrocyte density. The systemic effect involved impaired placental function and IGF signalling, revealing bone-placenta communication. Therefore, vertebrates, like invertebrates, can mount coordinated local and systemic responses to developmental insults that ensure that normal body proportions are maintained.
Assuntos
Desenvolvimento Ósseo/fisiologia , Animais , Evolução Biológica , Padronização Corporal/genética , Padronização Corporal/fisiologia , Desenvolvimento Ósseo/genética , Cartilagem/citologia , Cartilagem/embriologia , Cartilagem/metabolismo , Comunicação Celular/genética , Comunicação Celular/fisiologia , Contagem de Células , Pontos de Checagem do Ciclo Celular/genética , Pontos de Checagem do Ciclo Celular/fisiologia , Proliferação de Células , Condrócitos/citologia , Condrócitos/metabolismo , Inibidor de Quinase Dependente de Ciclina p21/genética , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Epífises/citologia , Epífises/embriologia , Epífises/metabolismo , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Membro Posterior/citologia , Membro Posterior/embriologia , Membro Posterior/metabolismo , Fator de Crescimento Insulin-Like II/genética , Fator de Crescimento Insulin-Like II/metabolismo , Masculino , Camundongos , Camundongos Transgênicos , Mosaicismo , Gravidez , Transdução de SinaisRESUMO
The main cell of origin of the Sonic hedgehog (SHH) subgroup of medulloblastoma (MB) is granule cell precursors (GCPs), a SHH-dependent transient amplifying population in the developing cerebellum. SHH-MBs can be further subdivided based on molecular and clinical parameters, as well as location because SHH-MBs occur preferentially in the lateral cerebellum (hemispheres). Our analysis of adult patient data suggests that tumors with Smoothened (SMO) mutations form more specifically in the hemispheres than those with Patched 1 (PTCH1) mutations. Using sporadic mouse models of SHH-MB with the two mutations commonly seen in adult MB, constitutive activation of Smo (SmoM2) or loss-of-Ptch1, we found that regardless of timing of induction or type of mutation, tumors developed primarily in the hemispheres, with SmoM2-mutants indeed showing a stronger specificity. We further uncovered that GCPs in the hemispheres are more susceptible to high-level SHH signaling compared with GCPs in the medial cerebellum (vermis), as more SmoM2 or Ptch1-mutant hemisphere cells remain undifferentiated and show increased tumorigenicity when transplanted. Finally, we identified location-specific GCP gene-expression profiles, and found that deletion of the genes most highly expressed in the hemispheres (Nr2f2) or vermis (Engrailed1) showed opposing effects on GCP differentiation. Our studies thus provide insights into intrinsic differences within GCPs that impact on SHH-MB progression.
Assuntos
Neoplasias Cerebelares/patologia , Cerebelo/patologia , Proteínas Hedgehog/metabolismo , Meduloblastoma/patologia , Receptor Patched-1/metabolismo , Receptor Smoothened/metabolismo , Adulto , Animais , Diferenciação Celular , Neoplasias Cerebelares/genética , Neoplasias Cerebelares/metabolismo , Cerebelo/metabolismo , Proteínas Hedgehog/genética , Humanos , Lactente , Meduloblastoma/genética , Meduloblastoma/metabolismo , Camundongos , Receptor Patched-1/genética , Transdução de Sinais , Receptor Smoothened/genética , TranscriptomaRESUMO
The cerebellum 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 cerebellum 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 cerebellum. Using mouse models, we found that the Hippo pathway transcriptional co-activator YAP1 (Yes-associated protein 1) but not TAZ (transcriptional coactivator with PDZ binding motif, or WWTR1) is required in NEPs for full recovery of cerebellar growth following irradiation one day after birth. Although Yap1 plays only a minor role during normal development in differentiation of NEPs or GCPs, the size of the cerebellum, and in particular the internal granule cell layer produced by GCPs, is significantly reduced in Yap1 mutants after irradiation, and the organization of Purkinje cells and Bergmann glial fibers is disrupted. The initial proliferative response of Yap1 mutant NEPs to irradiation is normal and the cells migrate to the GCP niche, but subsequently there is increased cell death of GCPs and altered migration of granule cells, possibly due to defects in Bergmann glia. Moreover, loss of Taz along with Yap1 in NEPs does not abrogate regeneration or alter development of the cerebellum. Our study provides new insights into the molecular signaling underlying postnatal cerebellar development and regeneration.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Proteínas de Ciclo Celular/fisiologia , Cerebelo/citologia , Células-Tronco Neurais/fisiologia , Aciltransferases , Proteínas Adaptadoras de Transdução de Sinal/genética , Animais , Encéfalo/efeitos da radiação , Lesões Encefálicas , Regeneração do Cérebro/fisiologia , Proteínas de Ciclo Celular/genética , Morte Celular , Movimento Celular , Cerebelo/crescimento & desenvolvimento , Cerebelo/lesões , Deleção de Genes , Camundongos , Nestina , Neuroglia/metabolismo , Transdução de Sinais , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas de Sinalização YAPRESUMO
PURPOSE: Genetically engineered mouse models of sporadic cancers are critical for studying tumor biology and for preclinical testing of therapeutics. We present an MRI-based pipeline designed to produce high resolution, quantitative information about tumor progression and response to novel therapies in mouse models of medulloblastoma (MB). METHODS: Sporadic MB was modeled in mice by inducing expression of an activated form of the Smoothened gene (aSmo) in a small number of cerebellar granule cell precursors. aSmo mice were imaged and analyzed at defined time-points using a 3D manganese-enhanced MRI-based pipeline optimized for high-throughput. RESULTS: A semi-automated segmentation protocol was established that estimates tumor volume in a time-frame compatible with a high-throughput pipeline. Both an empirical, volume-based classifier and a linear discriminant analysis-based classifier were tested to distinguish progressing from nonprogressing lesions at early stages of tumorigenesis. Tumor centroids measured at early stages revealed that there is a very specific location of the probable origin of the aSmo MB tumors. The efficacy of the manganese-enhanced MRI pipeline was demonstrated with a small-scale experimental drug trial designed to reduce the number of tumor associated macrophages and microglia. CONCLUSION: Our results revealed a high level of heterogeneity between tumors within and between aSmo MB models, indicating that meaningful studies of sporadic tumor progression and response to therapy could not be conducted without an imaging-based pipeline approach.
Assuntos
Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética , Meduloblastoma/diagnóstico por imagem , Algoritmos , Animais , Cerebelo/metabolismo , Análise Discriminante , Modelos Animais de Doenças , Progressão da Doença , Imageamento Tridimensional , Modelos Lineares , Camundongos , Reconhecimento Automatizado de Padrão , Transdução de Sinais , Receptor Smoothened/genéticaRESUMO
The mammalian cerebellum consists of folds of different sizes and shapes that house distinct neural circuits. A crucial factor underlying foliation is the generation of granule cells (gcs), the most numerous neuron type in the brain. We used clonal analysis to uncover global as well as folium size-specific cellular behaviors that underlie cerebellar morphogenesis. Unlike most neural precursors, gc precursors divide symmetrically, accounting for their massive expansion. We found that oriented cell divisions underlie an overall anteroposteriorly polarized growth of the cerebellum and gc clone geometry. Clone geometry is further refined by mediolateral oriented migration and passive dispersion of differentiating gcs. Most strikingly, the base of each fissure acts as a boundary for gc precursor dispersion, which we propose allows each folium to be regulated as a developmental unit. Indeed, the geometry and size of clones in long and short folia are distinct. Moreover, in engrailed 1/2 mutants with shorter folia, clone cell number and geometry are most similar to clones in short folia of wild-type mice. Thus, the cerebellum has a modular mode of development that allows the plane of cell division and number of divisions to be differentially regulated to ensure that the appropriate number of cells are partitioned into each folium.
Assuntos
Divisão Celular/fisiologia , Proliferação de Células/fisiologia , Cerebelo/embriologia , Interneurônios/citologia , Células-Tronco Neurais/fisiologia , Organogênese/fisiologia , Animais , Linhagem da Célula/fisiologia , Polaridade Celular/fisiologia , Imageamento Tridimensional , Imuno-Histoquímica , Camundongos , Microscopia de Fluorescência , Compostos de FenilureiaRESUMO
The hedgehog (HH) pathway is well known for its mitogenic and morphogenic functions during development, and HH signaling continues in discrete populations of cells within many adult mammalian tissues. Growing evidence indicates that HH regulates diverse quiescent stem cell populations, but the exact roles that HH signaling plays in adult organ homeostasis and regeneration remain poorly understood. Here, we review recently identified functions of HH in modulating the behavior of tissue-specific adult stem and progenitor cells during homeostasis, regeneration and disease. We conclude that HH signaling is a key factor in the regulation of adult tissue homeostasis and repair, acting via multiple different routes to regulate distinct cellular outcomes, including maintenance of plasticity, in a context-dependent manner.
Assuntos
Células-Tronco Adultas/fisiologia , Camadas Germinativas/metabolismo , Proteínas Hedgehog/metabolismo , Homeostase/fisiologia , Modelos Biológicos , Transdução de Sinais/fisiologia , Adulto , HumanosRESUMO
The prostate gland plays an important role in male reproduction, and is also an organ prone to diseases such as benign prostatic hyperplasia (BPH) and prostate cancer. The prostate consists of ducts with an inner layer of epithelium surrounded by stroma. Reciprocal signaling between these two cell compartments is instrumental to normal prostatic development, homeostasis, regeneration, as well as tumor formation. Hedgehog (HH) signaling is a master regulator in numerous developmental processes. In many organs, HH plays a key role in epithelial-mesenchymal signaling that regulates organ growth and tissue differentiation, and abnormal HH signaling has been implicated in the progression of various epithelial carcinomas. In this review, we focus on recent studies exploring the multipotency of endogenous postnatal and adult epithelial and stromal stem cells and studies addressing the role of HH in prostate development and cancer. We discuss the implications of the results for a new understanding of prostate development and disease. Insight into the cellular and molecular mechanisms underlying epithelial-mesenchymal growth regulation should provide a basis for devising innovative therapies to combat diseases of the prostate.
Assuntos
Células-Tronco Adultas/metabolismo , Transição Epitelial-Mesenquimal/fisiologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Proteínas Hedgehog/metabolismo , Próstata/embriologia , Próstata/crescimento & desenvolvimento , Neoplasias da Próstata/fisiopatologia , Transdução de Sinais/fisiologia , Animais , Humanos , Masculino , Camundongos , Próstata/metabolismo , Neoplasias da Próstata/metabolismo , Especificidade da EspécieRESUMO
The development of the mammalian cerebellum is orchestrated by both cell-autonomous programs and inductive environmental influences. Here, we describe the main processes of cerebellar ontogenesis, highlighting the neurogenic strategies used by developing progenitors, the genetic programs involved in cell fate specification, the progressive changes of structural organization, and some of the better-known abnormalities associated with developmental disorders of the cerebellum.
Assuntos
Cerebelo/embriologia , Cerebelo/crescimento & desenvolvimento , Animais , Cerebelo/citologia , Cerebelo/fisiopatologia , Consenso , Humanos , Neurogênese/fisiologia , Neurônios/citologia , Neurônios/fisiologiaRESUMO
Determining the cellular basis of brain growth is an important problem in developmental neurobiology. In the mammalian brain, the cerebellum is particularly amenable to studies of growth because it contains only a few cell types, including the granule cells, which are the most numerous neuronal subtype. Furthermore, in the mouse cerebellum granule cells are generated from granule cell precursors (gcps) in the external granule layer (EGL), from 1 day before birth until about 2 weeks of age. The complexity of the underlying cellular processes (multiple cell behaviors, three spatial dimensions, time-dependent changes) requires a quantitative framework to be fully understood. In this paper, a differential equation-based model is presented, which can be used to estimate temporal changes in granule cell numbers in the EGL. The model includes the proliferation of gcps and their differentiation into granule cells, as well as the process by which granule cells leave the EGL. Parameters describing these biological processes were derived from fitting the model to histological data. This mathematical model should be useful for understanding altered gcp and granule cell behaviors in mouse mutants with abnormal cerebellar development and cerebellar cancers.
Assuntos
Cerebelo/citologia , Cerebelo/crescimento & desenvolvimento , Neurônios/citologia , Algoritmos , Animais , Animais Recém-Nascidos , Diferenciação Celular , Cerebelo/embriologia , Simulação por Computador , Conceitos Matemáticos , Camundongos , Camundongos Mutantes Neurológicos , Modelos Neurológicos , Células-Tronco Neurais/citologia , Neurônios/classificaçãoRESUMO
The adult mouse prostate has a seemingly endless capacity for regeneration, and sonic hedgehog (SHH) signaling has been implicated in this stem cell-driven process. However, it is not clear whether SHH acts on the epithelium or stromal cells that secrete factors required for epithelial expansion. Because little is known about stromal stem cells compared with their epithelial counterparts, we used in vivo mouse genetics tools to characterize four prostate stromal subtypes and their stem cells. Using knockin reporter alleles, we uncovered that SHH signals from prostate basal epithelial cells to adjacent stromal cells. Furthermore, the SHH target gene Gli1 is preferentially expressed in subepithelial fibroblast-like cells, one of four prostate stromal subtypes and the subtype closest to the epithelial source of SHH. Using Genetic Inducible Fate Mapping to mark adult Gli1- or Smooth muscle actin-expressing cells and follow their fate during regeneration, we uncovered that Gli1-expressing cells exhibit long-term self-renewal capacity during multiple rounds of androgen-mediated regeneration after castration-induced involution, and depleted smooth muscle cells are mainly replenished by preexisting smooth muscle cells. Based on our Genetic Inducible Fate Mapping studies, we propose a model where SHH signals to multiple stromal stem cells, which are largely unipotent in vivo.
Assuntos
Proteínas Hedgehog/metabolismo , Modelos Biológicos , Próstata/metabolismo , Regeneração/fisiologia , Transdução de Sinais/fisiologia , Células-Tronco/metabolismo , Animais , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Proteínas Hedgehog/genética , Fatores de Transcrição Kruppel-Like/genética , Fatores de Transcrição Kruppel-Like/metabolismo , Masculino , Camundongos , Próstata/citologia , Células-Tronco/citologia , Células Estromais/citologia , Células Estromais/metabolismo , Proteína GLI1 em Dedos de ZincoRESUMO
Over the past two decades, the secreted protein sonic hedgehog (SHH) has emerged as a critical morphogen during embryonic lung development, regulating the interaction between epithelial and mesenchymal cell populations in the airway and alveolar compartments. There is increasing evidence that the SHH pathway is active in adult lung diseases such as pulmonary fibrosis, asthma, chronic obstructive pulmonary disease, and lung cancer, which raises two questions: (1) What role does SHH signaling play in these diseases? and (2) Is it a primary driver of the disease or a response (perhaps beneficial) to the primary disturbance? In this review we aim to fill the gap between the well-studied period of embryonic lung development and the adult diseased lung by reviewing the hedgehog (HH) pathway during the postnatal period and in adult uninjured and injured lungs. We elucidate the similarities and differences in the epithelial-mesenchymal interplay during the fibrosis response to injury in lung compared with other organs and present a critical appraisal of tools and agents available to evaluate HH signaling.