TEAD switches interacting partners along neural progenitor lineage progression to execute distinct functions

The TEAD family of transcription factors are best known as the DNA-binding factor in the Hippo pathway, where they act by interacting with transcriptional coactivators YAP and TAZ (YAP/TAZ). Despite the importance of the Hippo pathway, the in vivo functions of TEAD in mammals have not been well established. By comparing mouse mutants lacking TEAD1 and TEAD2 (TEAD1/2) to those lacking YAP/TAZ, we found that TEAD1/2 have both YAP/TAZ-dependent and -independent functions during ventral telencephalon development. TEAD1/2 loss and YAP/TAZ loss similarly disrupt neuroepithelial apical junctions. However, the impacts of their losses on progenitor lineage progression are essentially opposite: Whereas YAP/TAZ loss depletes early progenitors and increases later progenitors-consistent with their established function in promoting progenitor self-renewal and proliferation, TEAD1/2 loss expands early progenitors and reduces late progenitors, indicating that TEAD1/2 promote lineage progression. We further show that TEAD1/2 promote neural progenitor lineage progression by, at least in part, inhibiting Notch signaling and by cooperating with Insulinoma-associated 1 (INSM1). Orthologs of TEAD and INSM1 have been shown to cooperatively regulate neuronal cell fate decisions in worms and flies. Our study reveals a remarkable evolutionary conservation of the function of this transcription factor complex during metazoan neural development.

Neurogenesis in Caenorhabditis elegans

Animals rely on their nervous systems to process sensory inputs, integrate these with internal signals, and produce behavioral outputs. This is enabled by the highly specialized morphologies and functions of neurons. Neuronal cells share multiple structural and physiological features, but they also come in a large diversity of types or classes that give the nervous system its broad range of functions and plasticity. This diversity, first recognized over a century ago, spurred classification efforts based on morphology, function, and molecular criteria. Caenorhabditis elegans, with its precisely mapped nervous system at the anatomical level, an extensive molecular description of most of its neurons, and its genetic amenability, has been a prime model for understanding how neurons develop and diversify at a mechanistic level. Here, we review the gene regulatory mechanisms driving neurogenesis and the diversification of neuron classes and subclasses in C. elegans. We discuss our current understanding of the specification of neuronal progenitors and their differentiation in terms of the transcription factors involved and ensuing changes in gene expression and chromatin landscape. The central theme that has emerged is that the identity of a neuron is defined by modules of gene batteries that are under control of parallel yet interconnected regulatory mechanisms. We focus on how, to achieve these terminal identities, cells integrate information along their developmental lineages. Moreover, we discuss how neurons are diversified postembryonically in a time-, genetic sex-, and activity-dependent manner. Finally, we discuss how the understanding of neuronal development can provide insights into the evolution of neuronal diversity.

The Drosophila Hippo pathway transcription factor Scalloped and its co-factors alter each other's chromatin binding dynamics and transcription in vivo

The Hippo pathway is an important regulator of organ growth and cell fate. The major mechanism by which Hippo is known to control transcription is by dictating the nucleo-cytoplasmic shuttling rate of Yorkie, a transcription co-activator, which promotes transcription with the DNA binding protein Scalloped. The nuclear biophysical behavior of Yorkie and Scalloped, and whether this is regulated by the Hippo pathway, remains unexplored. Using multiple live-imaging modalities on Drosophila tissues, we found that Scalloped interacts with DNA on a broad range of timescales, and enrichment of Scalloped at sites of active transcription is mediated by longer DNA dwell times. Further, Yorkie increased Scalloped's DNA dwell time, whereas the repressors Nervous fingers 1 (Nerfin-1) and Tondu-domain-containing growth inhibitor (Tgi) decreased it. Therefore, the Hippo pathway influences transcription not only by controlling nuclear abundance of Yorkie but also by modifying the DNA binding kinetics of the transcription factor Scalloped.

NMY-2, TOE-2 and PIG-1 regulate Caenorhabditis elegans asymmetric cell divisions

Asymmetric cell division is an important mechanism that generates cellular diversity during development. Not only do asymmetric cell divisions produce daughter cells of different fates, but many can also produce daughters of different sizes, which we refer to as Daughter Cell Size Asymmetry (DCSA). In Caenorhabditis elegans, apoptotic cells are frequently produced by asymmetric divisions that exhibit DCSA, where the smaller daughter dies. We focus here on the divisions of the Q.a and Q.p neuroblasts, which produce larger surviving cells and smaller apoptotic cells and divide with opposite polarity using both distinct and overlapping mechanisms. Several proteins regulate DCSA in these divisions. Previous studies showed that the PIG-1/MELK and TOE-2 proteins regulate DCSA in both the Q.a and Q.p divisions, and the non-muscle myosin NMY-2 regulates DCSA in the Q.a division but not the Q.p division. In this study, we examined endogenously tagged NMY-2, TOE-2, and PIG-1 reporters and characterized their distribution at the cortex during the Q.a and Q.p divisions. In both divisions, TOE-2 localized toward the side of the dividing cell that produced the smaller daughter, whereas PIG-1 localized toward the side that produced the larger daughter. As previously reported, NMY-2 localized to the side of Q.a that produced the smaller daughter and did not localize asymmetrically in Q.p. We used temperature-sensitive nmy-2 mutants to determine the role of nmy-2 in these divisions and were surprised to find that these mutants only displayed DCSA defects in the Q.p division. We generated double mutant combinations between the nmy-2 mutations and mutations in toe-2 and pig-1. Because previous studies indicate that DCSA defects result in the transformation of cells fated to die into their sister cells, the finding that the nmy-2 mutations did not significantly alter the Q.a and Q.p DCSA defects of toe-2 and pig-1 mutants but did alter the number of daughter cells produced by Q.a and Q.p suggests that nmy-2 plays a role in specifying the fates of the Q.a and Q.p that is independent of its role in DCSA.

Control of successive unequal cell divisions by neural cell fate regulators determines embryonic neuroblast cell size

Asymmetric cell divisions often generate daughter cells of unequal size in addition to different fates. In some contexts, daughter cell size asymmetry is thought to be a key input to specific binary cell fate decisions. An alternative possibility is that unequal division is a mechanism by which a variety of cells of different sizes are generated during embryonic development. We show here that two unequal cell divisions precede neuroblast formation in the C lineage of Caenorhabditis elegans. The equalisation of these divisions in a pig-1/MELK mutant background has little effect on neuroblast specification. Instead, we demonstrate that let-19/MDT13 is a regulator of the proneural basic helix-loop-helix transcription factor hlh-14/ASCL1 and find that both are required to concomitantly regulate the acquisition of neuroblast identity and neuroblast cell size. Thus, embryonic neuroblast cell size in this lineage is progressively regulated in parallel with identity by key neural cell fate regulators. We propose that key cell fate determinants have a previously unappreciated function in regulating unequal cleavage, and therefore cell size, of the progenitor cells whose daughter cell fates they then go on to specify.

A plant flavonol and genetic suppressors rescue a pathogenic mutation associated with kinesin in neurons

KIF1A, a microtubule-based motor protein responsible for axonal transport, is linked to a group of neurological disorders known as KIF1A-associated neurological disorder (KAND). Current therapeutic options for KAND are limited. Here, we introduced the clinically relevant KIF1A(R11Q) variant into the Caenorhabditis elegans homolog UNC-104, resulting in uncoordinated animal behaviors. Through genetic suppressor screens, we identified intragenic mutations in UNC-104's motor domain that rescued synaptic vesicle localization and coordinated movement. We showed that two suppressor mutations partially recovered motor activity in vitro by counteracting the structural defect caused by R11Q at KIF1A's nucleotide-binding pocket. We found that supplementation with fisetin, a plant flavonol, improved KIF1A(R11Q) worms' movement and morphology. Notably, our biochemical and single-molecule assays revealed that fisetin directly restored the ATPase activity and processive movement of human KIF1A(R11Q) without affecting wild-type KIF1A. These findings suggest fisetin as a potential intervention for enhancing KIF1A(R11Q) activity and alleviating associated defects in KAND.

Mechanisms of lineage specification in Caenorhabditis elegans

The studies of cell fate and lineage specification are fundamental to our understanding of the development of multicellular organisms. Caenorhabditis elegans has been one of the premiere systems for studying cell fate specification mechanisms at single cell resolution, due to its transparent nature, the invariant cell lineage, and fixed number of somatic cells. We discuss the general themes and regulatory mechanisms that have emerged from these studies, with a focus on somatic lineages and cell fates. We next review the key factors and pathways that regulate the specification of discrete cells and lineages during embryogenesis and postembryonic development; we focus on transcription factors and include numerous lineage diagrams that depict the expression of key factors that specify embryonic founder cells and postembryonic blast cells, and the diverse somatic cell fates they generate. We end by discussing some future perspectives in cell and lineage specification.

Impairing one sensory modality enhances another by reconfiguring peptidergic signalling in Caenorhabditis elegans

Animals that lose one sensory modality often show augmented responses to other sensory inputs. The mechanisms underpinning this cross-modal plasticity are poorly understood. We probe such mechanisms by performing a forward genetic screen for mutants with enhanced O₂ perception in Caenorhabditis elegans. Multiple mutants exhibiting increased O₂ responsiveness concomitantly show defects in other sensory responses. One mutant, qui-1, defective in a conserved NACHT/WD40 protein, abolishes pheromone-evoked Ca²⁺ responses in the ADL pheromone-sensing neurons. At the same time, ADL responsiveness to pre-synaptic input from O₂-sensing neurons is heightened in qui-1, and other sensory defective mutants, resulting in enhanced neurosecretion although not increased Ca²⁺ responses. Expressing qui-1 selectively in ADL rescues both the qui-1 ADL neurosecretory phenotype and enhanced escape from 21% O₂. Profiling ADL neurons in qui-1 mutants highlights extensive changes in gene expression, notably of many neuropeptide receptors. We show that elevated ADL expression of the conserved neuropeptide receptor NPR-22 is necessary for enhanced ADL neurosecretion in qui-1 mutants, and is sufficient to confer increased ADL neurosecretion in control animals. Sensory loss can thus confer cross-modal plasticity by changing the peptidergic connectome.

The transcriptional corepressor CTBP-1 acts with the SOX family transcription factor EGL-13 to maintain AIA interneuron cell identity in Caenorhabditis elegans

Cell identity is characterized by a distinct combination of gene expression, cell morphology, and cellular function established as progenitor cells divide and differentiate. Following establishment, cell identities can be unstable and require active and continuous maintenance throughout the remaining life of a cell. Mechanisms underlying the maintenance of cell identities are incompletely understood. Here, we show that the gene ctbp-1, which encodes the transcriptional corepressor C-terminal binding protein-1 (CTBP-1), is essential for the maintenance of the identities of the two AIA interneurons in the nematode Caenorhabditis elegans. ctbp-1 is not required for the establishment of the AIA cell fate but rather functions cell-autonomously and can act in later larval stage and adult worms to maintain proper AIA gene expression, morphology and function. From a screen for suppressors of the ctbp-1 mutant phenotype, we identified the gene egl-13, which encodes a SOX family transcription factor. We found that egl-13 regulates AIA function and aspects of AIA gene expression, but not AIA morphology. We conclude that the CTBP-1 protein maintains AIA cell identity in part by utilizing EGL-13 to repress transcriptional activity in the AIAs. More generally, we propose that transcriptional corepressors like CTBP-1 might be critical factors in the maintenance of cell identities, harnessing the DNA-binding specificity of transcription factors like EGL-13 to selectively regulate gene expression in a cell-specific manner.

Comparison of differentiation gene batteries for migratory mechanosensory neurons across bilaterians

In embryos of distantly related bilaterian phyla, their lateral neural borders give rise to the peripheral nervous system elements, including various mechanosensory cells derived from migratory precursors, such as hair cells and dorsal root ganglion (DRG) neurons in vertebrates, bipolar tail neuron (BTN) in Ciona, chordotonal organ in Drosophila, and AVM/PVM in Caenorhabditis elegans. Developmental genetics studies had revealed a couple of transcription factors (TFs) regulating differentiation of mechanosensory cells shared by vertebrates and arthropods. However, unbiased systematic profiling of regulators is needed to demonstrate conservation of differentiation gene batteries for mechanosensory cells across bilaterians. At first, we observed that in both C. elegans Q neuroblasts and Drosophila lateral neuroectoderm, conserved NPB specifier Msx/vab-15 regulates Atoh1/lin-32, supporting the homology of mechanosensory neuron development in lateral neural border lineage of Ecdysozia. So we used C. elegans as a protostomia model. Single-cell resolution expression profiling of TFs and genetic analysis revealed a differentiation gene battery (Atonh1/lin-32, Drg11/alr-1, Gfi1/pag-3, Lhx5/mec-3, and Pou4/unc-86) for AVM/PVM mechanosensory neurons. The worm-gene battery significantly overlaps with both that of placode-derived Atonh1/lin-32-dependent hair cells and that of NPB-derived Neurogenin-dependent DRG neurons in vertebrates, supporting the homology of molecular mechanisms underlying the differentiation of neural border-derived mechanosensory cells between protostome and deuterostome. At last, Ciona BTN, the homolog of vertebrate DRG, also expresses Atonh1/lin-32, further supporting the homology notion and indicating a common origin of hair cells and DRG in vertebrate lineage.

Effect of STOX1 on recurrent spontaneous abortion by regulating trophoblast cell proliferation and migration via the PI3K/AKT signaling pathway

STOX1 is a transcription factor that is implicated in the high prevalence of human gestational diseases. It has been studied in various types of gestational diseases using different molecular and cellular biological technologies. However, the effect and detailed mechanism of storkhead box 1 (STOX1) in recurrent spontaneous abortion (RSA) remain unknown. This study aimed to explore the effect and detailed mechanism of STOX1 in human trophoblast cells. The result showed that downregulation of STOX1 by short hairpin RNA (shRNA) led to a decrease in proliferation and migration in HTR-8/SVneo cells, while it induced the apoptosis of HTR-8/SVneo cells. Moreover, the result showed that trophoblast cells expressed lower levels of pAKT and p85 subunits after treatment with STOX1 shRNA when compared with control. However, overexpression of STOX1 obviously increased the pAKT and p85 protein expressions. Transfection of pcDNA-AKT plasmid increased cell proliferation and migration in HTR-8/SVneo cells while suppressed the apoptosis of HTR-8/SVneo cells. Furthermore, inhibition of the PI3K/Akt pathway by a specific inhibitor promoted cell apoptosis and aggravatedly suppressed cell proliferation and migration of HTR-8/SVneo cells. On the other hand, upregulation of the PI3K/Akt pathway could increase the relative expression level of Bcl-2 and decrease the relative expression levels of Bax and Bim, while inhibition of the PI3K/Akt pathway led to adverse results. Our results demonstrated that inhibition of STOX1 could suppress trophoblast cell proliferation and migration, while promote apoptosis through inhibiting the PI3K/Akt signaling pathway. These findings might provide a new fundamental mechanism for regulating RSA and could be used to prevent and treat RSA in clinic.

Developmental Control of the Cell Cycle: Insights from Caenorhabditis elegans

During animal development, a single fertilized egg forms a complete organism with tens to trillions of cells that encompass a large variety of cell types. Cell cycle regulation is therefore at the center of development and needs to be carried out in close coordination with cell differentiation, migration, and death, as well as tissue formation, morphogenesis, and homeostasis. The timing and frequency of cell divisions are controlled by complex combinations of external and cell-intrinsic signals that vary throughout development. Insight into how such controls determine in vivo cell division patterns has come from studies in various genetic model systems. The nematode Caenorhabditis elegans has only about 1000 somatic cells and approximately twice as many germ cells in the adult hermaphrodite. Despite the relatively small number of cells, C. elegans has diverse tissues, including intestine, nerves, striated and smooth muscle, and skin. C. elegans is unique as a model organism for studies of the cell cycle because the somatic cell lineage is invariant. Somatic cells divide at set times during development to produce daughter cells that adopt reproducible developmental fates. Studies in C. elegans have allowed the identification of conserved cell cycle regulators and provided insights into how cell cycle regulation varies between tissues. In this review, we focus on the regulation of the cell cycle in the context of C. elegans development, with reference to other systems, with the goal of better understanding how cell cycle regulation is linked to animal development in general.

Inhibition of cell fate repressors secures the differentiation of the touch receptor neurons of Caenorhabditis elegans

Terminal differentiation generates the specialized features and functions that allow postmitotic cells to acquire their distinguishing characteristics. This process is thought to be controlled by transcription factors called 'terminal selectors' that directly activate a set of downstream effector genes. In Caenorhabditis elegans, the differentiation of both the mechanosensory touch receptor neurons (TRNs) and the multidendritic nociceptor FLP neurons uses the terminal selectors UNC-86 and MEC-3. The FLP neurons fail to activate TRN genes, however, because a complex of two transcriptional repressors (EGL-44/EGL-46) prevents their expression. Here, we show that the ZEB family transcriptional factor ZAG-1 promotes TRN differentiation not by activating TRN genes but by preventing the expression of EGL-44/EGL-46. As EGL-44/EGL-46 also inhibits the production of ZAG-1, these proteins form a bistable, negative-feedback loop that regulates the choice between the two neuronal fates.

The Caenorhabditis elegans gene ham-1 regulates daughter cell size asymmetry primarily in divisions that produce a small anterior daughter cell

C. elegans cell divisions that produce an apoptotic daughter cell exhibit Daughter Cell Size Asymmetry (DCSA), producing a larger surviving daughter cell and a smaller daughter cell fated to die. Genetic screens for mutants with defects in apoptosis identified several genes that are also required for the ability of these divisions to produce daughter cells that differ in size. One of these genes, ham-1, encodes a putative transcription factor that regulates a subset of the asymmetric cell divisions that produce an apoptotic daughter cell. In a survey of C. elegans divisions, we found that ham-1 mutations affect primarily anterior/posterior divisions that produce a small anterior daughter cell. The affected divisions include those that generate an apoptotic cell as well as those that generate two surviving cells. Our findings suggest that HAM-1 primarily promotes DCSA in a certain class of asymmetric divisions.

Separate transcriptionally regulated pathways specify distinct classes of sister dendrites in a nociceptive neuron

The dendritic processes of nociceptive neurons transduce external signals into neurochemical cues that alert the organism to potentially damaging stimuli. The receptive field for each sensory neuron is defined by its dendritic arbor, but the mechanisms that shape dendritic architecture are incompletely understood. Using the model nociceptor, the PVD neuron in C. elegans, we determined that two types of PVD lateral branches project along the dorsal/ventral axis to generate the PVD dendritic arbor: (1) Pioneer dendrites that adhere to the epidermis, and (2) Commissural dendrites that fasciculate with circumferential motor neuron processes. Previous reports have shown that the LIM homeodomain transcription factor MEC-3 is required for all higher order PVD branching and that one of its targets, the claudin-like membrane protein HPO-30, preferentially promotes outgrowth of pioneer branches. Here, we show that another MEC-3 target, the conserved TFIIA-like zinc finger transcription factor EGL-46, adopts the alternative role of specifying commissural dendrites. The known EGL-46 binding partner, the TEAD transcription factor EGL-44, is also required for PVD commissural branch outgrowth. Double mutants of hpo-30 and egl-44 show strong enhancement of the lateral branching defect with decreased numbers of both pioneer and commissural dendrites. Thus, HPO-30/Claudin and EGL-46/EGL-44 function downstream of MEC-3 and in parallel acting pathways to direct outgrowth of two distinct classes of PVD dendritic branches.

LIN-32/Atonal Controls Oxygen Sensing Neuron Development in Caenorhabditis elegans

Development of complex nervous systems requires precisely controlled neurogenesis. The generation and specification of neurons occur through the transcriptional and post-transcriptional control of complex regulatory networks. In vertebrates and invertebrates, the proneural basic-helix-loop-helix (bHLH) family of transcription factors has multiple functions in neurogenesis. Here, we identified the LIN-32/Atonal bHLH transcription factor as a key regulator of URXL/R oxygen-sensing neuron development in Caenorhabditis elegans. When LIN-32/Atonal expression is lost, the expression of URX specification and terminal differentiation genes is abrogated. As such, lin-32 mutant animals are unable to respond to increases in environmental oxygen. The URX neurons are generated from a branch of the cell lineage that also produces the CEPDL/R and URADL/R neurons. We found development of these neurons is also defective, suggesting that LIN-32/Atonal regulates neuronal development of the entire lineage. Finally, our results show that aspects of URX neuronal fate are partially restored in lin-32 mutant animals when the apoptosis pathway is inhibited. This suggests that, as in other organisms, LIN-32/Atonal regulates neuronal apoptosis.

Caenorhabditis elegans CES-1 Snail Represses pig-1 MELK Expression To Control Asymmetric Cell Division

Snail-like transcription factors affect stem cell function through mechanisms that are incompletely understood. In the Caenorhabditis elegans neurosecretory motor neuron (NSM) neuroblast lineage, CES-1 Snail coordinates cell cycle progression and cell polarity to ensure the asymmetric division of the NSM neuroblast and the generation of two daughter cells of different sizes and fates. We have previously shown that CES-1 Snail controls cell cycle progression by repressing the expression of cdc-25.2 CDC25. However, the mechanism through which CES-1 Snail affects cell polarity has been elusive. Here, we systematically searched for direct targets of CES-1 Snail by genome-wide profiling of CES-1 Snail binding sites and identified >3000 potential CES-1 Snail target genes, including pig-1, the ortholog of the oncogene maternal embryonic leucine zipper kinase (MELK). Furthermore, we show that CES-1 Snail represses pig-1 MELK transcription in the NSM neuroblast lineage and that pig-1 MELK acts downstream of ces-1 Snail to cause the NSM neuroblast to divide asymmetrically by size and along the correct cell division axis. Based on our results we propose that by regulating the expression of the MELK gene, Snail-like transcription factors affect the ability of stem cells to divide asymmetrically and, hence, to self-renew. Furthermore, we speculate that the deregulation of MELK contributes to tumorigenesis by causing cells that normally divide asymmetrically to divide symmetrically instead.

Conserved gene regulatory module specifies lateral neural borders across bilaterians

The lateral neural plate border (NPB), the neural part of the vertebrate neural border, is composed of central nervous system (CNS) progenitors and peripheral nervous system (PNS) progenitors. In invertebrates, PNS progenitors are also juxtaposed to the lateral boundary of the CNS. Whether there are conserved molecular mechanisms determining vertebrate and invertebrate lateral neural borders remains unclear. Using single-cell-resolution gene-expression profiling and genetic analysis, we present evidence that orthologs of the NPB specification module specify the invertebrate lateral neural border, which is composed of CNS and PNS progenitors. First, like in vertebrates, the conserved neuroectoderm lateral border specifier Msx/vab-15 specifies lateral neuroblasts in Caenorhabditis elegans Second, orthologs of the vertebrate NPB specification module (Msx/vab-15, Pax3/7/pax-3, and Zic/ref-2) are significantly enriched in worm lateral neuroblasts. In addition, like in other bilaterians, the expression domain of Msx/vab-15 is more lateral than those of Pax3/7/pax-3 and Zic/ref-2 in C. elegans Third, we show that Msx/vab-15 regulates the development of mechanosensory neurons derived from lateral neural progenitors in multiple invertebrate species, including C. elegans, Drosophila melanogaster, and Ciona intestinalis We also identify a novel lateral neural border specifier, ZNF703/tlp-1, which functions synergistically with Msx/vab-15 in both C. elegans and Xenopus laevis These data suggest a common origin of the molecular mechanism specifying lateral neural borders across bilaterians.

Comparative genetic, proteomic and phosphoproteomic analysis of C. elegans embryos with a focus on ham-1/STOX and pig-1/MELK in dopaminergic neuron development

Asymmetric cell divisions are required for cellular diversity and defects can lead to altered daughter cell fates and numbers. In a genetic screen for C. elegans mutants with defects in dopaminergic head neuron specification or differentiation, we isolated a new allele of the transcription factor HAM-1 [HSN (Hermaphrodite-Specific Neurons) Abnormal Migration]. Loss of both HAM-1 and its target, the kinase PIG-1 [PAR-1(I)-like Gene], leads to abnormal dopaminergic head neuron numbers. We identified discrete genetic relationships between ham-1, pig-1 and apoptosis pathway genes in dopaminergic head neurons. We used an unbiased, quantitative mass spectrometry-based proteomics approach to characterise direct and indirect protein targets and pathways that mediate the effects of PIG-1 kinase loss in C. elegans embryos. Proteins showing changes in either abundance, or phosphorylation levels, between wild-type and pig-1 mutant embryos are predominantly connected with processes including cell cycle, asymmetric cell division, apoptosis and actomyosin-regulation. Several of these proteins play important roles in C. elegans development. Our data provide an in-depth characterisation of the C. elegans wild-type embryo proteome and phosphoproteome and can be explored via the Encyclopedia of Proteome Dynamics (EPD) - an open access, searchable online database.

Prevention of medulla neuron dedifferentiation by Nerfin-1 requires inhibition of Notch activity

The Drosophila larval central nervous system comprises the central brain, ventral nerve cord and optic lobe. In these regions, neuroblasts (NBs) divide asymmetrically to self-renew and generate differentiated neurons or glia. To date, mechanisms of preventing neuron dedifferentiation are still unclear, especially in the optic lobe. Here, we show that the zinc-finger transcription factor Nerfin-1 is expressed in early-stage medulla neurons and is essential for maintaining their differentiation. Loss of Nerfin-1 activates Notch signaling, which promotes neuron-to-NB reversion. Repressing Notch signaling largely rescues dedifferentiation in nerfin-1 mutant clones. Thus, we conclude that Nerfin-1 represses Notch activity in medulla neurons and prevents them from dedifferentiation.

Size Matters: How C. elegans Asymmetric Divisions Regulate Apoptosis

Apoptosis is a form of programmed cell death used by metazoans to eliminate abnormal cells, control cell number, and shape the development of organs. The use of the nematode Caenorhabditis elegans as a model for the study of apoptosis has led to important insights into how cells die and how their corpses are removed. Eighty percent of these apoptotic cell deaths occur during nervous system development and in daughters of neuroblasts that divide asymmetrically. Pioneering work defined a conserved apoptosis pathway that is initiated in C. elegans by the BH3-only protein EGL-1 and that leads to the activation of the caspase CED-3. While the execution of the apoptotic fate is well understood, much less is known about the mechanisms that specify the apoptotic fate of particular cells. In some cells fated to die, this regulation occurs at the level of the egl-1 gene transcription, and investigators have identified several lineage-specific transcription factors that both positively and negatively regulate egl-1. In this review, we focus on a second set of molecules that appear to influence apoptosis by controlling the position of the cleavage plane in divisions that produce apoptotic cells.

Hippo kinases maintain polarity during directional cell migration in Caenorhabditis elegans

Precise positioning of cells is crucial for metazoan development. Despite immense progress in the elucidation of the attractive cues of cell migration, the repulsive mechanisms that prevent the formation of secondary leading edges remain less investigated. Here, we demonstrate that Caenorhabditis elegans Hippo kinases promote cell migration along the anterior-posterior body axis via the inhibition of dorsal-ventral (DV) migration. Ectopic DV polarization was also demonstrated in gain-of-function mutant animals for C. elegans RhoG MIG-2. We identified serine 139 of MIG-2 as a novel conserved Hippo kinase phosphorylation site and demonstrated that purified Hippo kinases directly phosphorylate MIG-2^S139 Live imaging analysis of genome-edited animals indicates that MIG-2^S139 phosphorylation impedes actin assembly in migrating cells. Intriguingly, Hippo kinases are excluded from the leading edge in wild-type cells, while MIG-2 loss induces uniform distribution of Hippo kinases. We provide evidence that Hippo kinases inhibit RhoG activity locally and are in turn restricted to the cell body by RhoG-mediated polarization. Therefore, we propose that the Hippo-RhoG feedback regulation maintains cell polarity during directional cell motility.

Stox1 as a novel transcriptional suppressor of Math1 during cerebellar granule neurogenesis and medulloblastoma formation

Cerebellar granule neuronal progenitors (GNPs) are the precursors of cerebellar granule cells (CGCs) and are believed to be the cell of origin for medulloblastoma (MB), yet the molecular mechanisms governing GNP neurogenesis are poorly elucidated. Here, we demonstrate that storkhead box 1 (Stox1), a forkhead transcriptional factor, has a pivotal role in cerebellar granule neurogenesis and MB suppression. Expression of Stox1 is upregulated along with GNP differentiation and repressed by activation of sonic hedgehog (SHH) signaling. Stox1 exerts its neurogenic and oncosuppressing effect via direct transcriptional repression of Math1, a basic helix-loop-helix transcription activator essential for CGC genesis. This study illustrates a SHH-Stox1-Math1 regulatory axis in normal cerebellar development and MB formation.

A map of terminal regulators of neuronal identity in Caenorhabditis elegans

Our present day understanding of nervous system development is an amalgam of insights gained from studying different aspects and stages of nervous system development in a variety of invertebrate and vertebrate model systems, with each model system making its own distinctive set of contributions. One aspect of nervous system development that has been among the most extensively studied in the nematode Caenorhabditis elegans is the nature of the gene regulatory programs that specify hardwired, terminal cellular identities. I first summarize a number of maps (anatomical, functional, and molecular) that describe the terminal identity of individual neurons in the C. elegans nervous system. I then provide a comprehensive summary of regulatory factors that specify terminal identities in the nervous system, synthesizing these past studies into a regulatory map of cellular identities in the C. elegans nervous system. This map shows that for three quarters of all neurons in the C. elegans nervous system, regulatory factors that control terminal identity features are known. In-depth studies of specific neuron types have revealed that regulatory factors rarely act alone, but rather act cooperatively in neuron-type specific combinations. In most cases examined so far, distinct, biochemically unlinked terminal identity features are coregulated via cooperatively acting transcription factors, termed terminal selectors, but there are also cases in which distinct identity features are controlled in a piecemeal fashion by independent regulatory inputs. The regulatory map also illustrates that identity-defining transcription factors are reemployed in distinct combinations in different neuron types. However, the same transcription factor can drive terminal differentiation in neurons that are unrelated by lineage, unrelated by function, connectivity and neurotransmitter deployment. Lastly, the regulatory map illustrates the preponderance of homeodomain transcription factors in the control of terminal identities, suggesting that these factors have ancient, phylogenetically conserved roles in controlling terminal neuronal differentiation in the nervous system. WIREs Dev Biol 2016, 5:474-498. doi: 10.1002/wdev.233 For further resources related to this article, please visit the WIREs website.

C. elegans HAM-1 functions in the nucleus to regulate asymmetric neuroblast division

All 302 neurons in the C. elegans hermaphrodite arise through asymmetric division of neuroblasts. During embryogenesis, the C. elegans ham-1 gene is required for several asymmetric neuroblast divisions in lineages that generate both neural and apoptotic cells. By antibody staining, endogenous HAM-1 is found exclusively at the cell cortex in many cells during embryogenesis and is asymmetrically localized in dividing cells. Here we show that in transgenic embryos expressing a functional GFP::HAM-1 fusion protein, GFP expression is also detected in the nucleus, in addition to the cell cortex. Consistent with the nuclear localization is the presence of a putative DNA binding winged-helix domain within the N-terminus of HAM-1. Through a deletion analysis we determined that the C-terminus of the protein is required for nuclear localization and we identified two nuclear localization sequences (NLSs). A subcellular fractionation experiment from wild type embryos, followed by Western blotting, revealed that endogenous HAM-1 is primarily found in the nucleus. Our analysis also showed that the N-terminus is necessary for cortical localization. While ham-1 function is essential for asymmetric division in the lineage that generates the PLM mechanosensory neuron, we showed that cortical localization may not required. Thus, our results suggest that there is a nuclear function for HAM-1 in regulating asymmetric neuroblast division and that the requirement for cortical localization may be lineage dependent.

Anillin Regulates Neuronal Migration and Neurite Growth by Linking RhoG to the Actin Cytoskeleton

Neuronal migration and neurite growth are essential events in neural development, but it remains unclear how guidance cues are transduced through receptors to the actin cytoskeleton, which powers these processes. We report that a cytokinetic scaffold protein, Anillin, is redistributed to the leading edge of the C. elegans Q neuroblast during cell migration and neurite growth. To bypass the requirement for Anillin in cytokinesis, we used the somatic CRISPR-Cas9 technique to generate conditional mutations in Anillin. We demonstrate that Anillin regulates cell migration and growth cone extension by stabilizing the F-actin network at the leading edge. Our biochemical analysis shows that the actin-binding domain of Anillin is sufficient to stabilize F-actin by antagonizing the F-actin severing activity of Cofilin. We further uncover that the active form of RhoG/MIG-2 directly binds to Anillin and recruits it to the leading edge. Our results reveal a novel pathway in which Anillin transduces the RhoG signal to the actin cytoskeleton during neuronal migration and neurite growth.

Transcription factor STOX1 regulates proliferation of inner ear epithelial cells via the AKT pathway

OBJECTIVES

Storkhead box 1 (STOX1) belongs to the forkhead family of transcription factors, and is reported to be involved in apoptosis of Caenorhabditis elegans. However, up to now the precise role of STOX1 in mammalian epithelial development has not been established. Here, we report that it plays an important role in regulation of proliferation of inner ear epithelial cells.

MATERIALS AND METHODS

Immunohistochemistry and reverse transcription-PCR assays were used to determine expression pattern of STOX1 in the mouse inner ear. Furthermore, its overexpression and knockdown effects on mouse inner ear epithelial cells were studied using RT-PCR, immunofluorescence, MTT assay, BrdU labelling and western blotting.

RESULTS

Storkhead box 1 was selectively expressed in epithelial cells, but not in stromal cells of the inner ear. Its over-expression enhanced cell proliferation and sphere formation, however, STOX1 knockdown inhibited cell proliferation and sphere formation in purified utricular epithelial cells in culture. Consistently, several cell cycle regulatory genes such as for PCNA, cyclin A and cyclin E, were up-regulated by STOX1 over-expression. Furthermore, biochemical analyses indicated that proliferation-promoting effects induced by STOX1 were mediated via phosphorylation of AKT in these cells.

CONCLUSIONS

Taken together, we demonstrate that STOX1 is a novel stimulatory factor for inner ear epithelial cell proliferation and might be an important target to be considered in regeneration or repair of inner ear epithelium.

A novel role for the zinc-finger transcription factor EGL-46 in the differentiation of gas-sensing neurons in Caenorhabditis elegans

Oxygen (O2) and carbon dioxide (CO2) provoke distinct olfactory behaviors via specialized sensory neurons across metazoa. In the nematode C. elegans, the BAG sensory neurons are specialized to sense changes in both O2 and CO2 levels in the environment. The precise functionality of these neurons is specified by the coexpression of a membrane-bound receptor-type guanylyl cyclase GCY-9 that is required for responses to CO2 upshifts and the soluble guanylyl cyclases GCY-31 and GCY-33 that mediate responses to downshifts in O2. Expression of these gas-sensing molecules in the BAG neurons is partially, although not completely, controlled by ETS-5, an ETS-domain-containing transcription factor, and EGL-13, a Sox transcription factor. We report here the identification of EGL-46, a zinc-finger transcription factor, which regulates BAG gas-sensing fate in partially parallel pathways to ETS-5 and EGL-13. Thereby, three conserved transcription factors collaborate to ensure neuron type-specific identity features of the BAG gas-sensing neurons.

Guangshuo Ou: New perspectives on Q cell biology

Ou studies asymmetric stem cell division and differentiation in C. elegans Q neuroblasts.

Conditional knockouts generated by engineered CRISPR-Cas9 endonuclease reveal the roles of coronin in C. elegans neural development

Conditional gene knockout animals are valuable tools for studying the mechanisms underlying cell and developmental biology. We developed a conditional knockout strategy by spatiotemporally manipulating the expression of an RNA-guided DNA endonuclease, CRISPR-Cas9, in Caenorhabditis elegans somatic cell lineages. We showed that this somatic CRISPR-Cas9 technology provides a quick and efficient approach to generate conditional knockouts in various cell types at different developmental stages. Furthermore, we demonstrated that this method outperforms our recently developed somatic TALEN technique and enables the one-step generation of multiple conditional knockouts. By combining these techniques with live-cell imaging, we showed that an essential embryonic gene, Coronin, which is associated with human neurobehavioral dysfunction, regulates actin organization and cell morphology during C. elegans postembryonic neuroblast migration and neuritogenesis. We propose that the somatic CRISPR-Cas9 platform is uniquely suited for conditional gene editing-based biomedical research.

A proneural gene controls C. elegans neuroblast asymmetric division and migration

Proneural genes control the generation of neuroblasts from the neuroepithelium, but their functions in neuroblast asymmetric division and migration remain elusive. Here, we identified Caenorhabditiselegans mutants of a proneural transcription factor (TF) lin-32, in which Q neuroblasts are produced. We showed that LIN-32 functions in parallel with a storkhead TF, HAM-1, to regulate Q neuroblast asymmetric division, and that Q neuroblast migration is inhibited in lin-32 alleles. Consistently, lin-32 is expressed throughout Q neuroblast lineage, suggesting that LIN-32 may promote different target gene expression. Our studies thus uncovered previously unknown functions of a proneural gene in neuroblast development.