Abnormal cerebellar development and Purkinje cell defects in Lgl1-Pax2 conditional knockout mice

Role of LGL1 in cerebellar primordium of embryonic mice

Lethal giant larvae 1 (LGL1) is originally recognized as a tumor suppressor, implicated in maintaining cell polarity in Drosophila and mammalian cells. Cell polarity plays a crucial role in tumorigenesis. We previously established Pax2-LGL1 -/- conditional knockout mice but did not focus on the tumorigenesis in cerebellar primordium. HE staining was used to detect the morphological structure of the cerebellar primordium during early embryonic development in Pax2-LGL1 -/- mice. Immunofluorescence assays were used to detect the expression of polar molecules. TUNEL staining assessed tissue apoptosis. Our findings reveal that deletion of LGL1 leads to the emergence of neuroblastoma-like tissues within the cerebellum primordium during early embryogenesis. This outcome can be attributed to alterations in expression patterns of polar molecules Cdc42 and β-catenin following early deletion of LGL1, resulting in loss of cell polarity among neuroepithelial cells and subsequent formation of tumor-like tissues. However, further histological examination demonstrated that these tumor-like tissues disappear from embryonic day 15.5 onwards within the cerebellar primordium of Pax2-LGL1 -/- mice due to apoptosis-mediated cellular compensation. Our data emphasize the importance of LGL1 in maintaining neuroepithelial cell polarity and reveal a novel role for LGL1 in regulating tumorigenesis and ablation in the cerebellar primordium.

Developmental and foliation changes due to dysregulation of adenosine kinase in the cerebellum

Adenosine kinase (ADK), the major adenosine-metabolizing enzyme, plays a key role in brain development and disease. In humans, mutations in the Adk gene have been linked to developmental delay, stunted growth, and intellectual disability. To better understand the role of ADK in brain development, it is important to dissect the specific roles of the two isoforms of the enzyme expressed in the cytoplasm (ADK-S) and cell nucleus (ADK-L). We, therefore, studied brain development in Adk-tg transgenic mice, which only express ADK-S in the absence of ADK-L throughout development. In the mutant animals, we found a reduction in the overall brain, body size, and weight during fetal and postnatal development. As a major developmental abnormality, we found a profound change in the foliation pattern of the cerebellum. Strikingly, our results indicated aberrant Purkinje cells arborization at P9 and accelerated cell death at P6 and P9. We found defects in cerebellar cell proliferation and migration using a bromodeoxyuridine (BrdU)-based cell proliferation assay at postnatal day 7. Our data demonstrate that dysregulation of ADK expression during brain development profoundly affects brain growth and differentiation.

Targeted Deletion of Loxl3 by Col2a1-Cre Leads to Progressive Hearing Loss

Collagens are major constituents of the extracellular matrix (ECM) that play an essential role in the structure of the inner ear and provide elasticity and rigidity when the signals of sound are received and transformed into electrical signals. LOXL3 is a member of the lysyl oxidase (LOX) family that are copper-dependent amine oxidases, generating covalent cross-links to stabilize polymeric elastin and collagen fibers in the ECM. Biallelic missense variant of LOXL3 was found in Stickler syndrome with mild conductive hearing loss. However, available information regarding the specific roles of LOXL3 in auditory function is limited. In this study, we showed that the Col2a1-Cre-mediated ablation of Loxl3 in the inner ear can cause progressive hearing loss, degeneration of hair cells and secondary degeneration of spiral ganglion neurons. The abnormal distribution of type II collagen in the spiral ligament and increased inflammatory responses were also found in Col2a1–Loxl3^–/– mice. Amino oxidase activity exerts an effect on collagen; thus, Loxl3 deficiency was expected to result in the instability of collagen in the spiral ligament and the basilar membrane, which may interfere with the mechanical properties of the organ of Corti and induce the inflammatory responses that are responsible for the hearing loss. Overall, our findings suggest that Loxl3 may play an essential role in maintaining hearing function.

A Microfluidic System to Measure Neonatal Lung Compliance Over Late Stage Development as a Functional Measure of Lung Tissue Mechanics

Premature birth interrupts the development of the lung, resulting in functional deficiencies and the onset of complex pathologies, like bronchopulmonary dysplasia (BPD), that further decrease the functional capabilities of the immature lung. The dysregulation of molecular targets has been implicated in the presentation of BPD, but there is currently no method to correlate resultant morphological changes observed in tissue histology with these perturbations to differences in function throughout saccular and alveolar lung development. Lung compliance is an aggregate measure of the lung's mechanical properties that is highly sensitive to a number of molecular, cellular, and architectural characteristics, but little is known about compliance in the neonatal mouse lung due to measurement challenges. We have developed a novel method to quantify changes in lung volume and pressure to determine inspiratory and expiratory compliance throughout neonatal mouse lung development. The compliance measurements obtained were validated against compliance values from published studies using mature lungs following enzymatic degradation of the extracellular matrix (ECM). The system was then used to quantify changes in compliance that occurred over the entire span of neonatal mouse lung development. These methods fill a critically important gap connecting powerful mouse models of development and disease to measures of functional lung mechanics critical to respiration and enable insights into the genetic, molecular, and cellular underpinnings of BPD pathology to improve lung function in premature infants.

Lgl1 deficiency disrupts hippocampal development and impairs cognitive performance in mice

Cellular polarity is crucial for brain development and morphogenesis. Lethal giant larvae 1 (Lgl1) plays a crucial role in the establishment of cell polarity from Drosophila to mammalian cells. Previous studies have found the importance of Lgl1 in the development of cerebellar, olfactory bulb, and cerebral cortex. However, the role of Lgl1 in hippocampal development during the embryonic stage and function in adult mice is still unknown. In our study, we created Lgl1-deficient hippocampus mice by using Emx1-Cre mice. Histological analysis showed that the Emx1-Lgl1^-/- mice exhibited reduced size of the hippocampus with severe malformations of hippocampal cytoarchitecture. These defects mainly originated from the disrupted hippocampal neuroepithelium, including increased cell proliferation, abnormal interkinetic nuclear migration, reduced differentiation, increased apoptosis, gradual disruption of adherens junctions, and abnormal neuronal migration. The radial glial scaffold was disorganized in the Lgl1-deficient hippocampus. Thus, Lgl1 plays a distinct role in hippocampal neurogenesis. In addition, the Emx1-Lgl1^-/- mice displayed impaired behavioral performance in the Morris water maze and fear conditioning test.

Early trigeminal ganglion afferents enter the cerebellum before the Purkinje cells are born and target the nuclear transitory zone

In the standard model for the development of climbing and mossy fiber afferent pathways to the cerebellum, the ingrowing axons target the embryonic Purkinje cell somata (around embryonic ages (E13-E16 in mice). In this report, we describe a novel earlier stage in afferent development. Immunostaining for a neurofilament-associated antigen (NAA) reveals the early axon distributions with remarkable clarity. Using a combination of DiI axon tract tracing, analysis of neurogenin1 null mice, which do not develop trigeminal ganglia, and mouse embryos maintained in vitro, we show that the first axons to innervate the cerebellar primordium as early as E9 arise from the trigeminal ganglion. Therefore, early trigeminal axons are in situ before the Purkinje cells are born. Double immunostaining for NAA and markers of the different domains in the cerebellar primordium reveal that afferents first target the nuclear transitory zone (E9-E10), and only later (E10-E11) are the axons, either collaterals from the trigeminal ganglion or a new afferent source (e.g., vestibular ganglia), seen in the Purkinje cell plate. The finding that the earliest axons to the cerebellum derive from the trigeminal ganglion and enter the cerebellar primordium before the Purkinje cells are born, where they seem to target the cerebellar nuclei, reveals a novel stage in the development of the cerebellar afferents.

Loss of Lgl1 Disrupts the Radial Glial Fiber-guided Cortical Neuronal Migration and Causes Subcortical Band Heterotopia in Mice

Radial glial cells (RGCs) are neuronal progenitors and function as scaffolds for neuronal radial migration in the developing cerebral cortex. These functions depend on a polarized radial glial scaffold, which is of fundamental importance for brain development. Lethal giant larvae 1 (Lgl1), a key regulator for cell polarity from Drosophila to mammals, plays a key role in tumorigenesis and brain development. To overcome neonatal lethality in Lgl1-null mice and clarify the role of Lgl1 in mouse cerebral cortex development and function, we created Lgl1 dorsal telencephalon-specific knockout mice mediated by Emx1-Cre. Lgl1^Emx1 conditional knockout (CKO) mice had normal life spans and could be used for function research. Histology results revealed that the mutant mice displayed an ectopic cortical mass in the dorsolateral hemispheric region between the normotopic cortex and the subcortical white matter, resembling human subcortical band heterotopia (SBH). The Lgl1^Emx1 CKO cortex showed disrupted adherens junctions (AJs), which were accompanied by ectopic RGCs and intermediate progenitors, and disorganization of the radial glial fiber system. The early- and late-born neurons failed to reach the destined position along the disrupted radial glial fiber scaffold and instead accumulated in ectopic positions and formed SBH. Additionally, the absence of Lgl1 led to severe abnormalities in RGCs, including hyperproliferation, impaired differentiation, and increased apoptosis. Lgl1^Emx1 CKO mice also displayed deficiencies in anxiety-related behaviors. We concluded that Lgl1 is essential for RGC development and neural migration during cerebral cortex development.

A compartmentalized phosphoinositide signaling axis at cilia is regulated by INPP5E to maintain cilia and promote Sonic Hedgehog medulloblastoma

Sonic Hedgehog (SHH) signaling at primary cilia drives the proliferation and progression of a subset of medulloblastomas, the most common malignant paediatric brain tumor. Severe side effects associated with conventional treatments and resistance to targeted therapies has led to the need for new strategies. SHH signaling is dependent on primary cilia for signal transduction suggesting the potential for cilia destabilizing mechanisms as a therapeutic target. INPP5E is an inositol polyphosphate 5-phosphatase that hydrolyses PtdIns(4,5)P₂ and more potently, the phosphoinositide (PI) 3-kinase product PtdIns(3,4,5)P₃. INPP5E promotes SHH signaling during embryonic development via PtdIns(4,5)P₂ hydrolysis at cilia, that in turn regulates the cilia recruitment of the SHH suppressor GPR161. However, the role INPP5E plays in cancer is unknown and the contribution of PI3-kinase signaling to cilia function is little characterized. Here, we reveal INPP5E promotes SHH signaling in SHH medulloblastoma by negatively regulating a cilia-compartmentalized PI3-kinase signaling axis that maintains primary cilia on tumor cells. Conditional deletion of Inpp5e in a murine model of constitutively active Smoothened-driven medulloblastoma slowed tumor progression, suppressed cell proliferation, reduced SHH signaling and promoted tumor cell cilia loss. PtdIns(3,4,5)P₃, its effector pAKT and the target pGSK3β, which when non-phosphorylated promotes cilia assembly/stability, localized to tumor cell cilia. The number of PtdIns(3,4,5)P₃/pAKT/pGSK3β-positive cilia was increased in cultured Inpp5e-null tumor cells relative to controls. PI3-kinase inhibition or expression of wild-type, but not catalytically inactive HA-INPP5E partially rescued cilia loss in Inpp5e-null tumor cells in vitro. INPP5E mRNA and copy number were reduced in human SHH medulloblastoma compared to other molecular subtypes and consistent with the murine model, reduced INPP5E was associated with improved overall survival. Therefore our study identifies a compartmentalized PtdIns(3,4,5)P₃/AKT/GSK3β signaling axis at cilia in SHH-dependent medulloblastoma that is regulated by INPP5E to maintain tumor cell cilia, promote SHH signaling and thereby medulloblastoma progression.

Molecular Programs Underlying Asymmetric Stem Cell Division and Their Disruption in Malignancy

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two unequal daughter cells. One retains its stem cell identity while the other becomes specialized through a differentiation program and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell in order to direct their destiny. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and non-canonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer.

Loss of Lysyl Oxidase-like 3 Attenuates Embryonic Lung Development in Mice

Lysyl oxidase-like 3 (LOXL3), a human disease gene candidate, is a member of the lysyl oxidase (LOX) family and is indispensable for mouse palatogenesis and vertebral column development. Our previous study showed that the loss of LOXL3 resulted in a severe cleft palate and spinal deformity. In this study, we investigated a possible role for LOXL3 in mouse embryonic lung development. LOXL3-deficient mice displayed reduced lung volumes and weights, diminished saccular spaces, and deformed and smaller thoracic cavities. Excess elastic fibres were detected in LOXL3-deficient lungs, which might be related to the increased LOXL4 expression. Increased transforming growth factor β1 (TGFβ1) expression might be involved in the up-regulation of LOXL4 in LOXL3-deficient lungs. We concluded that the loss of LOXL3 attenuates mouse embryonic lung development.

Lgl1 Is Required for Olfaction and Development of Olfactory Bulb in Mice

Lethal giant larvae 1 (Lgl1) was initially identified as a tumor suppressor in Drosophila and functioned as a key regulator of epithelial polarity and asymmetric cell division. In this study, we generated Lgl1 conditional knockout mice mediated by Pax2-Cre, which is expressed in olfactory bulb (OB). Next, we examined the effects of Lgl1 loss in the OB. First, we determined the expression patterns of Lgl1 in the neurogenic regions of the embryonic dorsal region of the LGE (dLGE) and postnatal OB. Furthermore, the Lgl1 conditional mutants exhibited abnormal morphological characteristics of the OB. Our behavioral analysis exhibited greatly impaired olfaction in Lgl1 mutant mice. To elucidate the possible mechanisms of impaired olfaction in Lgl1 mutant mice, we investigated the development of the OB. Interestingly, reduced thickness of the MCL and decreased density of mitral cells (MCs) were observed in Lgl1 mutant mice. Additionally, we observed a dramatic loss in SP8⁺ interneurons (e.g. calretinin and GABAergic/non-dopaminergic interneurons) in the GL of the OB. Our results demonstrate that Lgl1 is required for the development of the OB and the deletion of Lgl1 results in impaired olfaction in mice.

LKB1 Regulates Cerebellar Development by Controlling Sonic Hedgehog-mediated Granule Cell Precursor Proliferation and Granule Cell Migration

The Liver Kinase B1 (LKB1) gene plays crucial roles in cell differentiation, proliferation and the establishment of cell polarity. We created LKB1 conditional knockout mice (LKB1^Atoh1 CKO) to investigate the function of LKB1 in cerebellar development. The LKB1^Atoh1 CKO mice displayed motor dysfunction. In the LKB1^Atoh1 CKO cerebellum, the overall structure had a larger volume and morelobules. LKB1 inactivationled to an increased proliferation of granule cell precursors (GCPs), aberrant granule cell migration and overproduction of unipolar brush cells. To investigate the mechanism underlying the abnormal foliation, we examined sonic hedgehog signalling (Shh) by testing its transcriptional mediators, the Gli proteins, which regulate the GCPs proliferation and cerebellar foliation during cerebellar development. The expression levels of Gli genes were significantly increased in the mutant cerebellum. In vitro assays showed that the proliferation of cultured GCPs from mutant cerebellum significantly increased, whereas the proliferation of mutant GCPs significantly decreased in the presence of a Shh inhibitor GDC-0049. Thus, LKB1 deficiency in the LKB1^Atoh1 CKO mice enhanced Shh signalling, leading to the excessive GCP proliferation and the formation of extra lobules. We proposed that LKB1 regulates cerebellar development by controlling GCPs proliferation through Shh signalling during cerebellar development.

Cancer stem cell division: when the rules of asymmetry are broken

Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two daughter cells and simultaneously directs the differential fate of both: one retains its stem cell identity while the other becomes specialized and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and noncanonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer. The universe is asymmetric and I am persuaded that life, as it is known to us, is a direct result of the asymmetry of the universe or of its indirect consequences. The universe is asymmetric. -Louis Pasteur.