Stomatal patterning and differentiation by synergistic interactions of receptor kinases

Coordinated spacing and patterning of stomata allow efficient gas exchange between plants and the atmosphere. Here we report that three ERECTA (ER)-family leucine-rich repeat-receptor-like kinases (LRR-RLKs) together control stomatal patterning, with specific family members regulating the specification of stomatal stem cell fate and the differentiation of guard cells. Loss-of-function mutations in all three ER-family genes cause stomatal clustering. Genetic interactions with a known stomatal patterning mutant too many mouths (tmm) revealed stoichiometric epistasis and combination-specific neomorphism. Our findings suggest that the negative regulation of ER-family RLKs by TMM, which is an LRR receptor-like protein, is critical for proper stomatal differentiation.     

Interconversion between intestinal stem cell populations in distinct niches

Intestinal epithelial stem cell identity and location have been the subject of substantial research. Cells in the +4 niche are slow-cycling and label-retaining, whereas a different stem cell niche located at the crypt base is occupied by crypt base columnar (CBC) cells. CBCs are distinct from +4 cells, and the relationship between them is unknown, though both give rise to all intestinal epithelial lineages. We demonstrate that Hopx, an atypical homeobox protein, is a specific marker of +4 cells. Hopx-expressing cells give rise to CBCs and all mature intestinal epithelial lineages. Conversely, CBCs can give rise to +4 Hopx-positive cells. These findings demonstrate a bidirectional lineage relationship between active and quiescent stem cells in their niches.     

Generalized potential of adult neural stem cells

The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.     

Cell lineage analysis by intracellular injection of fluorescent tracers

Cell lineages during development of the leech are revealed by injection of a fluorescent peptide, rhodamine-D-peptide, into identified embryonic cells. Use of this peptide together with a nuclear stain showed a stereotypic cleavage pattern of stem cells and their progeny. Combined injection of rhodamine-D-peptide and pronase demonstrated the arrest of stem cell production in the pronase-injected teloblast.     

Polarization of the C. elegans embryo by RhoGAP-mediated exclusion of PAR-6 from cell contacts

Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR-6 to contact-free cell surfaces, where PAR-6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein (RhoGAP), PAC-1, which mediates C. elegans radial polarity and gastrulation by excluding PAR-6 from contacted cell surfaces. We show that PAC-1 is recruited to cell contacts, and we suggest that PAC-1 controls radial polarity by restricting active CDC-42 to contact-free surfaces, where CDC-42 binds and recruits PAR-6. Thus, PAC-1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially.     

Passive origins of stomatal control in vascular plants

Carbon and water flow between plants and the atmosphere is regulated by the opening and closing of minute stomatal pores in surfaces of leaves. By changing the aperture of stomata, plants regulate water loss and photosynthetic carbon gain in response to many environmental stimuli, but stomatal movements cannot yet be reliably predicted. We found that the complexity that characterizes stomatal control in seed plants is absent in early-diverging vascular plant lineages. Lycophyte and fern stomata are shown to lack key responses to abscisic acid and epidermal cell turgor, making their behavior highly predictable. These results indicate that a fundamental transition from passive to active metabolic control of plant water balance occurred after the divergence of ferns about 360 million years ago.     

Cytokinin signaling and its inhibitor AHP6 regulate cell fate during vascular development

The cell lineages that form the transporting tissues (xylem and phloem) and the intervening pluripotent procambial tissue originate from stem cells near the root tip. We demonstrate that in Arabidopsis, cytokinin phytohormones negatively regulate protoxylem specification. AHP6, an inhibitory pseudophosphotransfer protein, counteracts cytokinin signaling, allowing protoxylem formation. Conversely, cytokinin signaling negatively regulates the spatial domain of AHP6 expression. Thus, by controlling the identity of cell lineages, the reciprocal interaction of cytokinin signaling and its spatially specific modulator regulates proliferation and differentiation of cell lineages during vascular development, demonstrating a previously unrecognized regulatory circuit underlying meristem organization.     

Multilineage potential of adult human mesenchymal stem cells

Human mesenchymal stem cells are thought to be multipotent cells, which are present in adult marrow, that can replicate as undifferentiated cells and that have the potential to differentiate to lineages of mesenchymal tissues, including bone, cartilage, fat, tendon, muscle, and marrow stroma. Cells that have the characteristics of human mesenchymal stem cells were isolated from marrow aspirates of volunteer donors. These cells displayed a stable phenotype and remained as a monolayer in vitro. These adult stem cells could be induced to differentiate exclusively into the adipocytic, chondrocytic, or osteocytic lineages. Individual stem cells were identified that, when expanded to colonies, retained their multilineage potential.     

Intestinal stem cell replacement follows a pattern of neutral drift

With the capacity for rapid self-renewal and regeneration, the intestinal epithelium is stereotypical of stem cell-supported tissues. Yet the pattern of stem cell turnover remains in question. Applying analytical methods from population dynamics and statistical physics to an inducible genetic labeling system, we showed that clone size distributions conform to a distinctive scaling behavior at short times. This result demonstrates that intestinal stem cells form an equipotent population in which the loss of a stem cell is compensated by the multiplication of a neighbor, leading to neutral drift dynamics in which clones expand and contract at random until they either take over the crypt or they are lost. Combined with long-term clonal fate data, we show that the rate of stem cell replacement is comparable to the cell division rate, implying that neutral drift and symmetrical cell divisions are central to stem cell homeostasis.     

麦类和黍类作物光合器官细胞形态和光合性能的比较（综述）

本文比较了麦类和黍类作物在光合器官细胞形态和光合性能方面的异同点。与黍类作物相比,麦类作物的叶肉细胞较大,且形态和组成较复杂;叶片的气孔密度较低;叶片的细胞形态随叶位上升逐步复杂化的趋势较明显,规律性也较强。黍类作物的光合速率一般高于麦类作物。麦类和黍类作物光合作用的日变化形式也有不同。麦类作物除叶片以外的绿色器官,具有与叶肉细胞类似的光合细胞,且有较强的光合功能,而黍类作物的这一特点不明显。     

Dynamic imaging of T cell-dendritic cell interactions in lymph nodes

T cell immune responses begin within organized lymphoid tissues. The pace, topology, and outcomes of the cellular interactions that underlie these responses have, so far, been inferred from static imaging of sectioned tissue or from studies of cultured cells. Here we report dynamic visualization of antigen-specific T cells interacting with dendritic cells within intact explanted lymph nodes. We observed immunological synapse formation and prolonged interactions between these two cell types, followed by the activation, dissociation, and rapid migration of T cells away from the antigenic stimulus. This high-resolution spatiotemporal analysis provides insight into the nature of cell interactions critical to early immune responses within lymphoid structures.     

鳞毛蕨科8种蕨类植物叶表皮特征的比较形态学研究

利用光学显微镜对鳞毛蕨科6种鳞毛蕨属植物和2种耳蕨属植物叶表皮特征进行比较观察和分析.结果表明:8种蕨类植物的叶片表面无附属物;气孔器类型具多型现象,鳞毛蕨属植物气孔器类型主要为不等细胞型和极细胞型,耳蕨属植物气孔器类型多为无规则四细胞型;气孔均为下生型,不下陷,多沿叶脉方向排列,且叶脉间分布较密集;鳞毛蕨属植物气孔器较耳蕨属狭长,表皮细胞为不规则型,垂周壁呈波状或不规则凹凸状,而耳蕨属植物表皮细胞狭长,垂周壁为浅波状;6种鳞毛蕨气孔器指数总体上较耳蕨属大,而气孔器密度差异不大.由此得出结论,表皮的整体特征可以作为划分鳞毛蕨科植物的特征;可据细胞大小、气孔器大小与气孔器指数来区别鳞毛蕨属和耳蕨属植物,为鳞毛蕨属植物的分类鉴定提供了新的形态学依据.     

B cell ligand discrimination through a spreading and contraction response

B cells recognize foreign antigens by virtue of cell surface immunoglobulin receptors and are most effectively activated by membrane-bound ligands. Here, we show that in the early stages of this process, B cells exhibit a two-phase response in which they first spread over the antigen-bearing membrane and then contract, thereby collecting bound antigen into a central aggregate. The extent of this response, which is both signaling- and actin-dependent, determines the quantity of antigen accumulated and hence the degree of B cell activation. Brownian dynamic simulations reproduce essential features of the antigen collection process and suggest a possible basis for affinity discrimination. We propose that dynamic spreading is an important step of the immune response.     

Control of stomatal distribution on the Arabidopsis leaf surface

Stomata regulate gas exchange and are distributed across the leaf epidermis with characteristic spacing. Arabidopsis stomata are produced by asymmetric cell divisions. Mutations in the gene TOO MANY MOUTHS (TMM) disrupt patterning by randomizing the plane of formative asymmetric divisions and by permitting ectopic divisions. TMM encodes a leucine-rich repeat-containing receptor-like protein expressed in proliferative postprotodermal cells. TMM appears to function in a position-dependent signaling pathway that controls the plane of patterning divisions as well as the balance between stem cell renewal and differentiation in stomatal and epidermal development.     

大鼠心肌条件培养基在昆明白小鼠胚胎干细胞分离培养中的效果

采用大鼠心肌条件培养基对昆明白小鼠胚胎干细胞进行分离、消化传代、培养鉴定等,研究大鼠心肌条件培养基在昆明白小鼠胚胎干细胞分离培养中的作用效果。结果显示,SD大鼠心肌条件培养基在昆明白小鼠3.5d囊胚胚胎干细胞集落分离中,所分离的昆明白小鼠胚胎干细胞集落具有岛屿状生长,隆起于饲养层上;碱性磷酸酶染色为强阳性;体外分化可形成类胚体状结构,贴壁的类胚体周边会出现许多分化的上皮样细胞或单个散在的细胞;经过常规冻存传代的胚胎干细胞集落具有较为一致的生长形态,并呈现胚胎干细胞集落所特有的岛屿状生长形态;对传至第5代的小鼠胚胎干细胞集落进行核型分析,小鼠胚胎干细胞核型正常率大于75%。试验证实,SD大鼠心肌条件培养基在昆明白小鼠胚胎干细胞分离培养过程中效果较好。     

Cadherin cell adhesion receptors as a morphogenetic regulator

Cadherins are a family of cell adhesion receptors that are crucial for the mutual association of vertebrate cells. Through their homophilic binding interactions, cadherins play a role in cell-sorting mechanisms, conferring adhesion specificities on cells. The regulated expression of cadherins also controls cell polarity and tissue morphology. Cadherins are thus considered to be important regulators of morphogenesis. Moreover, pathological examinations suggest that the down-regulation of cadherin expression is associated with the invasiveness of tumor cells.     

The molecular control of blood cell development

The establishment of a cell culture system for the clonal development of blood cells has made it possible to identify the proteins that regulate the growth and differentiation of different blood cell lineages and to discover the molecular basis of normal and abnormal cell development in blood forming tissues. A model system with myeloid blood cells has shown that (i) normal blood cells require different proteins to induce cell multiplication (growth inducers) and cell differentiation (differentiation inducers), (ii) there is a hierarchy of growth inducers as cells become more restricted in their developmental program, and (iii) a cascade of interactions between proteins determines the correct balance between immature and mature cells in normal blood cell development. Gene cloning has shown that there is a family of different genes for these proteins. Normal protein regulators of blood cell development can control the abnormal growth of certain types of leukemic cells and suppress malignancy by inducing differentiation to mature nondividing cells. Chromosome abnormalities that give rise to malignancy in these leukemic cells can be bypassed and their effects nullified by inducing differentiation, which stops cells from multiplying. These blood cell regulatory proteins are active in culture and in the body, and they can be used clinically to correct defects in blood cell development.     

Mathematical modeling of planar cell polarity to understand domineering nonautonomy

Planar cell polarity (PCP) signaling generates subcellular asymmetry along an axis orthogonal to the epithelial apical-basal axis. Through a poorly understood mechanism, cell clones that have mutations in some PCP signaling components, including some, but not all, alleles of the receptor frizzled, cause polarity disruptions of neighboring wild-type cells, a phenomenon referred to as domineering nonautonomy. Here, a contact-dependent signaling hypothesis, derived from experimental results, is shown by reaction-diffusion, partial differential equation modeling and simulation to fully reproduce PCP phenotypes, including domineering nonautonomy, in the Drosophila wing. The sufficiency of this model and the experimental validation of model predictions reveal how specific protein-protein interactions produce autonomy or domineering nonautonomy.     

百合叶表皮微形态观察

利用光学显微镜对4种野生百合和14个百合品种叶片上、下表皮进行研究,并测量气孔的大小、密度及表皮细胞大小、侧向垂周壁长及式样等性状。结果表明：百合气孔多为椭圆形,均分布于叶片的下表皮;保卫细胞为肾形,无副卫细胞;叶表皮细胞近似于长方形,垂周壁式样分为平直、浅波状、深波状三种。所得数据通过SPSS13.0软件进行聚类分析,聚类结果较好反映出试验材料的亲缘关系。