Xiangming Wang

Conditional targeted genome editing using somatically expressed TALENs in C. elegans

We have developed a method for the generation of conditional knockouts in Caenorhabditis elegans by expressing transcription activator–like effector nucleases (TALENs) in somatic cells. Using germline transformation with plasmids encoding TALENs under the control of an inducible or tissue-specific promoter, we observed effective gene modifications and resulting phenotypes in specific developmental stages and tissues. We further used this method to bypass the embryonic requirement of cor-1, which encodes the homolog of human severe combined immunodeficiency (SCID) protein coronin, and we determined its essential role in cell migration in larval Q-cell lineages. Our results show that TALENs expressed in the somatic cells of model organisms provide a versatile tool for functional genomics.

Live imaging of cellular dynamics during Caenorhabditis elegans postembryonic development

Postembryonic development is an important process of organismal maturation after embryonic growth. Despite key progress in recent years in understanding embryonic development via fluorescence time-lapse microscopy, comparatively less live-cell imaging of postembryonic development has been done. Here we describe a protocol to image larval development in the nematode Caenorhabditis elegans. Our protocol describes the construction of fluorescent transgenic C. elegans, immobilization of worm larvae and time-lapse microscopy analysis. To improve the throughput of imaging, we developed a C. elegans triple-fluorescence imaging approach with a worm-optimized blue fluorescent protein (TagBFP), green fluorescent protein (GFP) and mCherry. This protocol has been previously applied to time-lapse imaging analysis of Q neuroblast asymmetric division, migration and apoptosis, and we show here that it can also be used to image neuritogenesis in the L1 larvae. Other applications are also possible. The protocol can be completed within 3 h and may provide insights into understanding postembryonic development.

Transmembrane protein MIG-13 links the Wnt signaling and Hox genes to the cell polarity in neuronal migration

Directional cell migration is a fundamental process in neural development. In Caenorhabditis elegans, Q neuroblasts on the left (QL) and right (QR) sides of the animal generate cells that migrate in opposite directions along the anteroposterior body axis. The homeobox (Hox) gene lin-39 promotes the anterior migration of QR descendants (QR.x), whereas the canonical Wnt signaling pathway activates another Hox gene, mab-5, to ensure the QL descendants’ (QL.x) posterior migration. However, the regulatory targets of LIN-39 and MAB-5 remain elusive. Here, we showed that MIG-13, an evolutionarily conserved transmembrane protein, cell-autonomously regulates the asymmetric distribution of the actin cytoskeleton in the leading migratory edge. We identified mig-13 as a cellular target of LIN-39 and MAB-5. LIN-39 establishes QR.x anterior polarity by binding to the mig-13 promoter and promoting mig-13 expression, whereas MAB-5 inhibits QL.x anterior polarity by associating with the lin-39 promoter and downregulating lin-39 and mig-13 expression. Thus, MIG-13 links the Wnt signaling and Hox genes that guide migrations, to the actin cytoskeleton, which executes the motility response in neuronal migration.

Lifespan extension in Caenorhabditis elegans by DMSO is dependent on sir-2.1 and daf-16.

Dimethyl sulfoxide (DMSO) is an important solvent that is widely used in industry and medical studies, as well as in the study of aging, in which it is used as a negative control for lifespan assays; however, our data showed that 0.5% and 2% DMSO extended the lifespan of Caenorhabditis elegans by 24.4% and 23.0% (the first trial), respectively. Treatment with 0.5% DMSO did not affect the progeny number or the lifespan of C. elegans under thermal stress. Using real time reverse transcription-polymerase chain reaction (RT-PCR), we found that the expression levels of hsp-16.2, hsp-70, lys-7, old-1, and sod-5 were enhanced by 2.5, 2.9, 1.3, 2.3, and 4.5-fold, respectively, after treatment with 0.5% DMSO. This suggests that these genes downstream of DAF-16 might function in the lifespan extension properties of DMSO. Using the transgenic strain lys-7::GFP, we found that treatment with 0.5% DMSO also caused expression levels of lys-7 increased by 1.5-fold. Genetic analysis using mutants of aging-related genes showed that lifespan extension in C. elegans by DMSO was dependent on sir-2.1 and daf-16 but not eat-2 or hsf-1. In summary, we report the function and the putative mechanism of DMSO in lifespan extension of C. elegans. This study draws attention to using DMSO as a solvent when conducting aging studies.

Developmental stage-dependent transcriptional regulatory pathways control neuroblast lineage progression

Neuroblasts generate neurons with different functions by asymmetric cell division, cell cycle exit and differentiation. The underlying transcriptional regulatory pathways remain elusive. Here, we performed genetic screens in C. elegans and identified three evolutionarily conserved transcription factors (TFs) essential for Q neuroblast lineage progression. Through live cell imaging and genetic analysis, we showed that the storkhead TF HAM-1 regulates spindle positioning and myosin polarization during asymmetric cell division and that the PAR-1-like kinase PIG-1 is a transcriptional regulatory target of HAM-1. The TEAD TF EGL-44, in a physical association with the zinc-finger TF EGL-46, instructs cell cycle exit after the terminal division. Finally, the Sox domain TF EGL-13 is necessary and sufficient to establish the correct neuronal fate. Genetic analysis further demonstrated that HAM-1, EGL-44/EGL-46 and EGL-13 form three transcriptional regulatory pathways. We have thus identified TFs that function at distinct developmental stages to ensure appropriate neuroblast lineage progression and suggest that their vertebrate homologs might similarly regulate neural development.

The heparan sulfate-modifying enzyme glucuronyl C5-epimerase HSE-5 controls Caenorhabditis elegans Q neuroblast polarization during migration.

Directional cell migration is fundamental for neural development, and extracellular factors are pivotal for this process. Heparan sulfate proteoglycans (HSPGs) that carry long chains of differentially modified sugar residues contribute to extracellular matrix; however, the functions of HSPG in guiding cell migration remain elusive. Here, we used the Caenorhabditis elegans mutant pool from the Million Mutation Project and isolated a mutant allele of the heparan sulfate-modifying enzyme glucuronyl C5-epimerase HSE-5. Loss-of-function of this enzyme resulted in defective Q neuroblast migration. We showed that hse-5 controlled Q cell migration in a cell non-autonomous manner. By performing live cell imaging in hse-5 mutant animals, we found that hse-5 controlled initial polarization during Q neuroblast migration. Furthermore, our genetic epistasis analysis demonstrated that lon-2 might act downstream of hse-5. Finally, rescue of the hse-5 mutant phenotype by expression of human and mouse hse-5 homologs suggested a conserved function for this gene in neural development. Taken together, our results indicated that proper HSPG modification in the extracellular matrix by HSE-5 is essential for neuroblast polarity during migration.

Receptor tyrosine phosphatase CLR-1 acts in skin cells to promote sensory dendrite outgrowth.

Sensory dendrite morphogenesis is directed by intrinsic and extrinsic factors. The extracellular environment plays instructive roles in patterning dendrite growth and branching. However, the molecular mechanism is not well understood. In Caenorhabditis elegans, the proprioceptive neuron PVD forms highly branched sensory dendrites adjacent to the hypodermis. We report that receptor tyrosine phosphatase CLR-1 functions in the hypodermis to pattern the PVD dendritic branches. Mutations in clr-1 lead to loss of quaternary branches, reduced secondary branches and increased ectopic branches. CLR-1 is necessary for the dendrite extension but not for the initial filopodia formation. Its role is dependent on the intracellular phosphatase domain but not the extracellular adhesion domain, indicating that it functions through dephosphorylating downstream factors but not through direct adhesion with neurons. Genetic analysis reveals that clr-1 also functions in parallel with SAX-7/DMA-1 pathway to control PVD primary dendrite development. We provide evidence of a new environmental factor for PVD dendrite morphogenesis.

Effect of Erzhi Pill (二至丸) on Improving Cerebral Nerve Cell Apoptosis in Aging Rats

ObjectiveTo investigate the effects of Erzhi Pill (二至丸,EZP) on nerve cell apoptosis in senescence model rats.MethodsThe rats model of senescence was established by peritoneal D-galactose injection combined with thymusectomy. Forty SD rats were randomized into four groups, the normal control group, the senescence model group, the EZP treated group, and the vitamins treated group, 10 in each group. The rats were made into senescence model except those in the normal group. In the same time of D-galactose injection, the rats were treated respectively with distilled water, EZP 4.32 g/kg, and vitamins E and C 0.06 g/kg daily for 6 weeks via intragastric infusion. The index of main viscera (as brain, testis, etc.), serum levels of superoxide dismutase (SOD) activity, and total anti-oxidation capacity (T-AOC) were measured after a 6-week treatment. Meanwhile, the cerebral cortex neuronal apoptosis proportion and mitochondrial membrane potential (MMP) were detected by flow cytometry.ResultsBoth EZP and vitamins E and C treatments showed effects on increasing testis index and serum level of T-AOC, reducing the percentage of neuronal apoptosis in the cerebral cortex, and elevating MMP in the aging rats model.ConclusionsEZP could inhibit the cerebral cortex neuron apoptosis and maintain the mitochondrial function in the senescent process of rats induced by peritoneal D-galactose injection combined with thymusectomy. It also shows antioxidation effect to some extents.

The Function of a Spindle Checkpoint Gene bub-1 in C. elegans Development

Background The serine/threonine kinase BUB1 (Budding Uninhibited by Benzimidazole 1) was originally identified in yeast as a checkpoint protein, based on its mutants incapacity of delaying the cell cycle in response to loss of microtubules. Our understanding of its function is primarily from studies carried out in yeast S. cerevisiae. It has been shown that it is a component of the mitotic spindle checkpoint and regulates the separation of sister chromatids through its downstream molecules. However, its roles in multi-cellular organisms remain unclear. Methods and Findings In nematode C. elegans, rapid cell divisions primarily occur in embryos and in germline of postembryonic larvae and adults. In addition, a select set of cells undergo a few rounds of cell division postembryonically. One common phenotype associated with impaired cell division is described as Stu (Sterile and Uncoordinated) [1], [2]. We conducted a genetic screen for zygotic mutants that displayed Stu phenotype in C. elegans. We isolated seven Stu mutants that fell into five complementation groups. We report here that two mutations, FanWang5 (fw5) and FanWang8 (fw8) affect the bub-1 gene, a homolog of yeast BUB1. Both mutant alleles of fw5 and fw8 exhibited variable behavioral defects, including developmental arrest, uncoordination and sterility. The number of postembryonically born neurons in the ventral cord decreased and their axon morphology was abnormal. Also, the decrease of neurons in the ventral cord phenotype could not be suppressed by a caspase-3 loss-of-function mutant. In addition, bub-1(fw5 and fw8) mutants showed widespread effects on postembryonic development in many cell lineages. We found that bub-1 functioned maternally in several developmental lineages at the embryonic stage in C. elegans. Studies in yeast have shown that BUB1 functions as a spindle checkpoint protein by regulating the anaphase promoting complex/cyclosome (APC/C). We performed double mutant analysis and observed that bub-1 genetically interacted with several downstream genes, including fzy-1/CDC20, mat-2/APC1 and emb-27/APC6. Conclusions Our results demonstrate a conserved role of bub-1 in cell-cycle regulation and reveal that C. elegans bub-1 is required both maternally and zygotically. Further, our genetic analysis is consistent with that the function of bub-1 in C. elegans is likely similar to its yeast and mammalian homologs.

Dynein and EFF-1 control dendrite morphology by regulating the localization pattern of SAX-7 in epidermal cells

ABSTRACT Our previous work showed that the cell adhesion molecule SAX-7 forms an elaborate pattern in Caenorhabditis elegans epidermal cells, which instructs PVD dendrite branching. However, the molecular mechanism forming the SAX-7 pattern in the epidermis is not fully understood. Here, we report that the dynein light intermediate chain DLI-1 and the fusogen EFF-1 are required in epidermal cells to pattern SAX-7. While previous reports suggest that these two molecules act cell-autonomously in the PVD, our results show that the disorganized PVD dendritic arbors in these mutants are due to the abnormal SAX-7 localization patterns in epidermal cells. Three lines of evidence support this notion. First, the epidermal SAX-7 pattern was severely affected in dli-1 and eff-1 mutants. Second, the abnormal SAX-7 pattern was predictive of the ectopic PVD dendrites. Third, expression of DLI-1 or EFF-1 in the epidermis rescued both the SAX-7 pattern and the disorganized PVD dendrite phenotypes, whereas expression of these molecules in the PVD did not. We also show that DLI-1 functions cell-autonomously in the PVD to promote distal branch formation. These results demonstrate the unexpected roles of DLI-1 and EFF-1 in the epidermis in the control of PVD dendrite morphogenesis. Summary: Dynein and EFF-1 have a non-autonomous function in patterning PVD dendrites in C. elegans through epidermal SAX-7.