Eukaryotic cells and their cell bodies: Cell Theory revised

BACKGROUND: Cell Theory, also known as cell doctrine, states that all eukaryotic organisms are composed of cells, and that cells are the smallest independent units of life. This Cell Theory has been influential in shaping the biological sciences ever since, in 1838/1839, the botanist Matthias Schleiden and the zoologist Theodore Schwann stated the principle that cells represent the elements from which all plant and animal tissues are constructed. Some 20 years later, in a famous aphorism Omnis cellula e cellula, Rudolf Virchow annunciated that all cells arise only from pre-existing cells. General acceptance of Cell Theory was finally possible only when the cellular nature of brain tissues was confirmed at the end of the 20th century. Cell Theory then rapidly turned into a more dogmatic cell doctrine, and in this form survives up to the present day. In its current version, however, the generalized Cell Theory developed for both animals and plants is unable to accommodate the supracellular nature of higher plants, which is founded upon a super-symplasm of interconnected cells into which is woven apoplasm, symplasm and super-apoplasm. Furthermore, there are numerous examples of multinucleate coenocytes and syncytia found throughout the eukaryote superkingdom posing serious problems for the current version of Cell Theory. SCOPE: To cope with these problems, we here review data which conform to the original proposal of Daniel Mazia that the eukaryotic cell is composed of an elemental Cell Body whose structure is smaller than the cell and which is endowed with all the basic attributes of a living entity. A complement to the Cell Body is the Cell Periphery Apparatus, which consists of the plasma membrane associated with other periphery structures. Importantly, boundary structures of the Cell Periphery Apparatus, although capable of some self-assembly, are largely produced and maintained by Cell Body activities and can be produced from it de novo. These boundary structures serve not only as mechanical support for the Cell Bodies but they also protect them from the hostile external environment and from inappropriate interactions with adjacent Cell Bodies within the organism. CONCLUSIONS: From the evolutionary perspective, Cell Bodies of eukaryotes are proposed to represent vestiges of hypothetical, tubulin-based 'guest' proto-cells. After penetrating the equally hypothetical actin-based 'host' proto-cells, tubulin-based 'guests' became specialized for transcribing, storing and partitioning DNA molecules via the organization of microtubules. The Cell Periphery Apparatus, on the other hand, represents vestiges of the actin-based 'host' proto-cells which have become specialized for Cell Body protection, shape control, motility and for actin-mediated signalling across the plasma membrane.     

Time and cell systems as variables in fusion experiments with polyethylene glycol

Summary Cell hybridization was done between a monolayer of B14-150 Chinese hamster cells and a suspension of either mouse leukemia cells or normal human lymphocytes. Cell contact was obtained by centrifugation of the suspension cells onto the monolayer cells in a culture plate. Cell fusion was done by means of polyethylene glycol (PEG). The optimum time for PEG exposure as well as the yield of hybrid cells differed markedly with the different combinations.     

Asymmetric cell division of a triangular halophilic archaebacterium

Abstract The cell division of the halophilic archaebacterium, Haloarcula japonicus , which has a characteristic triangular shape in high salt concentration media, was analysed by time lapse microscopic cinematography. Cell division on an agar medium occured on average every 3.7 h. Cell plates were laid down asymmetrically, generating triangular or rhomboid shape daughter cells which then separated. Cell plate formation was clearly observed because the cells are flat and thin enough to see through using a conventional light microscope.     

Uncapping the potential of renal stem cells

In this issue of Cell Stem Cell, McMahon and coworkers (Kobayashi et al., 2008) characterize a subset of progenitor cells in the developing kidney. six2-expressing mesenchymal cells exhibit hallmark stem cell traits, in that they appear to self-renew and are clonally multipotent for a range of nephron epithelial cell types.     

Sensitivity of the mosquito Aedes aegypti (Culicidae) labral apical chemoreceptors to blood plasma components

The phagostimulants from the cellular fraction of blood induce gorging of Aedes aegypti (L.), and this process is enhanced by some plasma components. This project examines the responses of the labral apical chemoreceptors to plasma components enhancing phagostimulation. From the electrophysiological responses of the labral apical chemoreceptors four cells were identified by the waveform of their action potentials. Three of the cells (Cell 2, Cell 3 and Cell 4) responded in a dose dependent manner to NaCl. The responses of Cell 2 and Cell 3 to NaCl concentrations from 1 to 500 mmol/l can be described by a logarithmic equation. The response of Cell 2 to 150 mmol/l NaCl is modulated when a buffer is added. The magnitude of the modulation of the response is determined by the nature of the buffer: NaHCO(3) inhibits while Na(2)HPO(4) enhances the response. High osmotic pressure inhibits the response of Cell 4, regardless of how it is achieved. Cell 4 responds with a high frequency to the presence of L-alanine, the C-terminal amino acid of albumin, but shows a reduced response to the same concentration of albumin. From these results it can be concluded that labral apical chemoreceptors of A. aegypti are capable of detecting the plasma components involved in blood recognition.     

Connecting cancer to the asymmetric division of stem cells

Two studies, one in this issue of Cell and the other in Developmental Cell show that the cell-fate determinant Brain Tumor (Brat) suppresses self-renewal in one of the daughter cells that arise from the asymmetric division of a neural stem cell. This work suggests a mechanism by which loss of polarity in stem cells may lead to tumorigenesis.     

Defining the pathways of early adult hematopoiesis

The journeys that hematopoietic cells take to differentiate from long-term stem cells into committed cells have recently been a topic of debate. In this issue of Cell Stem Cell, Arinobu et al. (2007) and Pronk et al. (2007) provide new insights into the paths traveled by hematopoietic progenitors.     

Stem Cell Epigenetics: Is It All Downhill from Here?

In this issue of Cell Stem Cell, Fasano et al. (2007) investigate the role of Bmi-1 in neural stem cells in vitro and in vivo. They find a progressively increasing requirement for Bmi-1 function in stem cells during development that, surprisingly, seems to involve regulation of the cell-cycle inhibitor p21.     

Stem cells remember their grade

The stem cell state is understood based on what cells do in performance assays, crude measures of a highly refined state. In this issue of Cell Stem Cell, Dykstra et al. (2007) reveal stem cell gradation and the extent to which that gradation is retained in stem cell daughters of hematopoietic stem cells.     

Waste management and adult neurogenesis

Dying cells are common in adult neurogenic niches, but how these cells are cleared remains uncertain. In this issue of Cell Stem Cell, Sierra et al. (2010) show that unactivated microglia assume the role of waste managers to eliminate cellular debris from apoptosing newborn cells in the hippocampus.     

Myeloproliferative disorder by TKO

In this issue of Cell Stem Cell, Viatour et al. (2008) delete all three members of the retinoblastoma tumor suppressor gene family in hematopoietic stem cells, resulting in a myeloproliferative disorder. The disease was cell autonomous and resulted from alterations in the primitive hematopoietic cells.     

Cancer: Inappropriate Expression of Stem Cell Programs?

Cancer stem cells (CSCs) are a subpopulation of cancer cells that possess characteristics, including self-renewal, associated with normal stem cells. In this issue of Cell Stem Cell, Wong et al. (2008) define a core embryonic stem cell (ESC)-like gene expression program that may be important for CSC function in multiple epithelial cancers.     

细胞药物的种类及生物学特性——细胞药物连载之一

细胞药物是以不同细胞为基础的用于疾病治疗的制剂、药物或产品的统称,是继放疗、化疗之后又一种临床有效的治疗手段,可实施个性化治疗。细胞药物的种类很多,按其生物学特性可分为传统体细胞、免疫细胞以及各种不同的干细胞等。经体外操作过的细胞群,如肝细胞、胰岛细胞、软骨细胞、树突状细胞、细胞因子诱导的杀伤细胞、淋巴因子激活的杀伤细胞、体外加工的骨髓或造血干细胞和体外处理的肿瘤细胞(瘤苗)等。细胞药物已在一些难治性疾病中得到应用,包括血液系统疾病、心血管系统疾病、消化系统疾病、神经系统疾病、免疫系统疾病和抗衰老等。细胞治疗涉及的细胞种类很多,且不同细胞或不同治疗方法各有特点。运用不同的细胞药物来修复病变细胞,以重建受损的功能细胞和组织,恢复其生物学功能,为细胞丢失或损伤性疾病的防治提供了崭新的思路。     

Chemotherapy and cancer stem cells

Cancer stem cells are subsets of tumor cells defined through the capacity to initiate tumors and have been linked to therapeutic resistance. In this issue of Cell Stem Cell, Todaro et al. (2007) demonstrate that targeting tumor IL-4 sensitizes colon cancer stem cells to chemotherapy.     

Changing places: a novel type of niche and stem cell coordination in the Drosophila ovary

The Drosophila ovary has been a favorite model for the study of stem cells within their niche. In this issue of Cell Stem Cell, Nystul and Spradling (2007) study somatic stem cells within a novel kind of niche and reveal the complexity and coordination of stem cell behavior.     

Generation of transplantable striatal projection neurons from human ESCs

In this issue of Cell Stem Cell, Ma et?al. (2012) report a differentiation protocol for generating striatal projection neurons from human embryonic stem cells with high efficiency. The cells survive transplantation, reconnect striatal circuitry, and restore motor function in a mouse model of striatal neurodegeneration that mimics the central pathohology of Huntington's disease.     

沉默FOXQ1可逆转SW480细胞的上皮-间质转化

FOXQ1是FOX家族的的重要成员之一,其参与了多种人类肿瘤的上皮间质转化(epithelial- mesenchymal transition,EMT).本研究设计合成了FOXQ1基因的shRNA（short hairpin RNA）,用此转染SW480细胞,通过显微镜观察细胞形态,Transwell小室、细胞黏附试验检测转移能力及黏附能力,以探索FOXQ1与结直肠癌细胞EMT的关系.结果显示,沉默FOXQ1后,SW480细胞顶底极性及细胞间紧密连接增加,侵袭、迁移的细胞数目减少,同种黏附能力增加,异种黏附能力降低.进一步的机制研究表明,沉默FOXQ1基因可以导致SW480细胞的上皮标志因子E-cadherin表达显著增高,而间质细胞标志因子N-cadherin、Vimentin及MMP2表达均降低.以上结果表明,沉默FOXQ1基因可以逆转SW480细胞EMT,其机制可能与E-cadherin的上调和N cadherin、Vimentin、MMP2的下调有关,这为进一步研究FOXQ1在结直肠癌发生发展中的作用提供实验基础.     

Cellular Differentiation in a Highly Specialized Insect Secretory Organ

The colleterial glands of insects are accessory reproductive structures which produce secretions that are applied to eggs after fertilization and which serve a number of protective functions. The colleterial glands of lepidoptera are of particular interest in the study of the events of cellular differentiation because they undergo rapid development, generally during the pupal adult transformation, and contain highly specialized cells which produce large amounts of a restricted variety of secretory products. The extreme specialization of these organs facilitates parallel studies of differentiation at the biochemical and morphological level. This communication describes the changes in the ultrastructure of cells which will form the protein-secreting segment of the colleterial gland of the moth Actias luna during the period of transition from the undifferentiated state to the acquisition of secretory ability.
An initial stage of general cellular proliferation by mitosis in the presumptive colleterial tissue mass is followed by differentiation of the cells in the absence of further mitosis. Four distinctive cell types are recognized during the phase of differentiation. These types include a chitogenous cell which forms the chitin lining of the main duct, and three cells which cooperate in the formation of a secretory apparatus. Cell A forms two temporary flagella-like structures which assist in the formation of a ductule, which eventually leads from the secretory cell to the main duct. Near the end of the differentiative phase, Cell A degenerates and is phagocitized by Cell B. Cell B becomes the actual secretory element, and acquires cytoplasmic features such as extensive rough endoplasmic reticulum and Golgi apparatus which are associated with synthesis and secretion of protein. The final element, Cell C, remains associated with the ductule which it helps to construct and which traverses its cytoplasm.