Cytoplasmic partitioning of P granule components is not required to specify the germline in C. elegans

Asymmetric segregation of P granules during the first four divisions of the Caenorhabditis elegans embryo is a classic example of cytoplasmic partitioning of germline determinants. It is thought that asymmetric partitioning of P granule components during mitosis is essential to distinguish germline from soma. We have identified a mutant (pptr-1) in which P granules become unstable during mitosis and P granule proteins and RNAs are distributed equally to somatic and germline blastomeres. Despite symmetric partitioning of P granule components, pptr-1 mutants segregate a germline that uniquely expresses P granules during postembryonic development. pptr-1 mutants are fertile, except at high temperatures. Hence, asymmetric partitioning of maternal P granules is not essential to specify germ cell fate. Instead, it may serve to protect the nascent germline from stress.     

Male germline stem cells: from mice to men

The production of functional male gametes is dependent on the continuous activity of germline stem cells. The availability of a transplantation assay system to unequivocally identify male germline stem cells has allowed their in vitro culture, cryopreservation, and genetic modification. Moreover, the system has enabled the identification of conditions and factors involved in stem cell self-renewal, the foundation of spermatogenesis, and the production of spermatozoa. The increased knowledge about these cells is also of great potential practical value, for example, for the possible cryopreservation of stem cells from boys undergoing treatment for cancer to safeguard their germ line.     

Redox regulation of germline and vulval development in Caenorhabditis elegans

In vitro studies have indicated that reactive oxygen species (ROS) and the oxidation of signaling molecules are important mediators of signal transduction. We have identified two pathways by which the altered redox chemistry of the clk-1 mutants of Caenorhabditis elegans acts in vivo on germline development. One pathway depends on the oxidation of an analog of vertebrate low density lipoprotein (LDL) and acts on the germline through the Ack-related tyrosine kinase (ARK-1) kinase and inositol trisphosphate (IP3) signaling. The other pathway is the oncogenic ras signaling pathway, whose action on germline as well as vulval development appears to be modulated by cytoplasmic ROS.     

Translational regulators maintain totipotency in the Caenorhabditis elegans germline

The molecular mechanisms that maintain totipotency of the germline are not well understood. Here, we show that two conserved translational regulators, MEX-3 and GLD-1, are essential for maintaining totipotency in the Caenorhabditis elegans germline. In mex-3 gld-1 mutants, germ cells transdifferentiate into various somatic cell types such as muscles or neurons. Our findings implicate RNA regulation in the maintenance of totipotency, suggest that multiple mechanisms maintain totipotency at different stages of germline development, and establish a genetically tractable model for studying the development of teratomas.     

Male and female Drosophila germline stem cells: two versions of immortality

Drosophila male and female germline stem cells (GSCs) are sustained by niches and regulatory pathways whose common principles serve as models for understanding mammalian stem cells. Despite striking cellular and genetic similarities that suggest a common evolutionary origin, however, male and female GSCs also display important differences. Comparing these two stem cells and their niches in detail is likely to reveal how a common heritage has been adapted to the differing requirements of male and female gamete production.     

Anterior-posterior polarity in C. elegans and Drosophila--PARallels and differences

The eggs of Caenorhabditis elegans and Drosophila bear little similarity to each other, yet both depend on the par genes for control of anterior-posterior polarity. Here we explore possible common roles for the par genes (pars) in converting transient asymmetries into stably polarized axes. Although clear mechanistic parallels remain to be established, par-dependent regulation of microtubule dynamics and protein stability emerge as common themes.     

新生牛雄性生殖干细胞的分离纯化与培养

为建立新生牛雄性生殖干细胞的体外增殖与分化体系,将新生牛睾丸消化成单细胞悬液,分别进行差速贴壁、不连续密度梯度Percoll分选雄性生殖干细胞和支持细胞,对分选生殖干细胞进行体外培养。结果表明,差速贴壁法能有效分选雄性生殖干细胞与支持细胞,2%血清浓度的培养液即可用于雄性生殖干细胞的体外培养,添加100 ng·mL-1的GDNF能显著促进雄性生殖干细胞的增殖,增殖形成的雄性生殖干细胞集落具有一定多能性。     

Neurexin and neuroligin mediate retrograde synaptic inhibition in C. elegans

The synaptic adhesion molecules neurexin and neuroligin alter the development and function of synapses and are linked to autism in humans. Here, we found that Caenorhabditis elegans neurexin (NRX-1) and neuroligin (NLG-1) mediated a retrograde synaptic signal that inhibited neurotransmitter release at neuromuscular junctions. Retrograde signaling was induced in mutants lacking a muscle microRNA (miR-1) and was blocked in mutants lacking NLG-1 or NRX-1. Release was rapid and abbreviated when the retrograde signal was on, whereas release was slow and prolonged when retrograde signaling was blocked. The retrograde signal adjusted release kinetics by inhibiting exocytosis of synaptic vesicles (SVs) that are distal to the site of calcium entry. Inhibition of release was mediated by increased presynaptic levels of tomosyn, an inhibitor of SV fusion.     

Roles for mating and environment in C. elegans sex determination

In Caenorhabditis elegans the two sexes, hermaphrodites and males, are thought to be irreversibly determined at fertilization by the ratio of X chromosomes to sets of autosomes: XX embryos develop as hermaphrodites and XO embryos as males. We show instead that both sex and genotype of C. elegans can be altered postembryonically and that this flexibility requires sexual reproduction. When grown in specific bacterial metabolites, some XX larvae generated by mating males and hermaphrodites develop as males and lose one X chromosome. However, XX larvae produced by hermaphrodite self-fertilization show no such changes. We propose that sexual reproduction increases developmental flexibility of progeny, allowing for better adaptation to changing environments.     

稻种资源的储藏特性与抗氧化代谢的关系

对68份不同进化阶段、不同种皮色稻种资源的储藏特性、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、还原型谷胱甘肽(GSH)、花色苷含量、1,2-二苯基苦基苯肼清除率(SFRC)进行测定,研究稻种储藏过程中体内自由基清除率、抗氧化相关酶类和非酶抗氧化物质的变化.结果表明,稻种资源的储藏特性、自由基清除率(SFRC)、抗氧化相关酶类和非酶抗氧化物质存在显著的基因型差异.老化指数与SFRC、花色苷、GSH、POD呈负相关,SFRC与SOD、CAT呈正相关,与种皮中花色苷含量呈极显著正相关(r=0.641**).随着储藏时间的延长,其体内抗氧化酶(SOD、POD、CAT)活性逐渐降低,GSH、SFRC也呈下降的趋势,而花色苷含量变化不显著.该研究结果为利用稻种资源的有益基因,开展耐储藏专用型水稻品种选育奠定了基础.     

Genome-wide prediction of C. elegans genetic interactions

To obtain a global view of functional interactions among genes in a metazoan genome, we computationally integrated interactome data, gene expression data, phenotype data, and functional annotation data from three model organisms-Saccharomyces cerevisiae, Caenorhabditis elegans, and Drosophila melanogaster-and predicted genome-wide genetic interactions in C. elegans. The resulting genetic interaction network (consisting of 18,183 interactions) provides a framework for system-level understanding of gene functions. We experimentally tested the predicted interactions for two human disease-related genes and identified 14 new modifiers.     

Wolbachia enhance Drosophila stem cell proliferation and target the germline stem cell niche

Wolbachia are widespread maternally transmitted intracellular bacteria that infect most insect species and are able to alter the reproduction of innumerous hosts. The cellular bases of these alterations remain largely unknown. Here, we report that Drosophila mauritiana infected with a native Wolbachia wMau strain produces about four times more eggs than the noninfected counterpart. Wolbachia infection leads to an increase in the mitotic activity of germline stem cells (GSCs), as well as a decrease in programmed cell death in the germarium. Our results suggest that up-regulation of GSC division is mediated by a tropism of Wolbachia for the GSC niche, the cellular microenvironment that supports GSCs.     

Suspended animation in C. elegans requires the spindle checkpoint

In response to environmental signals such as anoxia, many organisms enter a state of suspended animation, an extreme form of quiescence in which microscopically visible movement ceases. We have identified a gene, san-1, that is required for suspended animation in Caenorhabditis elegans embryos. We show that san-1 functions as a spindle checkpoint component in C. elegans. During anoxia-induced suspended animation, embryos lacking functional SAN-1 or a second spindle checkpoint component, MDF-2, failed to arrest the cell cycle, exhibited chromosome missegregation, and showed reduced viability. These data provide a model for how a dynamic biological process is arrested in suspended animation.