Ultrastructure of the Fusion Area during Conjugation in the Suctorian Heliphrya erhardi (Rieder) Matthes*

SYNOPSIS. The suctorian Heliophrya erhardi (Rieder) Matthes is attached to the substrate by the flattened ventral side of the cell body. The dorsal is covered by a pellicle composed of 3 unit membranes. Below the pellicle is a 0.4–0.8-μm thick epiplasm composed of 6–8-nm thick fibrils. Microtubules form a network beneath the epiplasm. The epipalsm is penetrated by tube-like pellicular pits, which are lined by the cell membrane and end beneath the epiplasm in a saccule-like enlargement. During conjugation, 2 neighboring organisms form cytoplasmic processes which come into contact and fuse, thus forming a cytoplasmic bridge between the 2 cells. Around the bridge the pellicles of both organisms fuse, and the partners become united by a continuous common membrane system. Across the entire conjugation bridge the 2 fused epiplasms form a septum. Tube-like structures can be seen lying partly in the epiplasmic septum and partly in the adjacent cytoplasm. These structures are open at both ends and represent remnants of the pellicular pits. No trace of the original pellicular membranes can be found at the fusion area within the epiplasmic septum. The cytoplasm of the conjugation partners is separated only by the fused epiplasms forming the epiplasmic septum.     

Histopathology of roots of Glycine max (L.) Merrill induced by root-knot nematode (Meloidogyne incognita)

In Glycine max, the second-stage juveniles of Meloidogyne incognita entered the roots through the apical meristem or elongation zone. The juveniles induced giant cells in the zone of vascular strands. Near the head of the nematode and adjacent to the giant cells, the vascular strands exhibited abnormalities in their shapes and structures; both xylem and phloem were found to be affected. The giant cells had dense and granular cytoplasm, and large nuclei with large nucleoli. Some parenchyma cells exhibited hypertrophy, while others exhibited hyperplasia. The distinctive feature of the study is reporting the occurrence of abnormal xylem, abnormal phloem and abnormal parenchyma.     

The role of unequal cleavage and the polar lobe in the segregation of developmental potential during first cleavage in the embryo of Chætopterus variopedatus

Summary The inequality of the first cleavage division of the Chætopterus embryo is caused by the production of a small polar lobe and the internal shifting of the first cleavage spindle. This division produces a two-celled embryo containing a small AB and a large CD blastomere. These blastomeres have different morphogenetic potentials. Only the larvae resulting from isolated CD blastomeres are able to form bioluminescent photocytes, eyes and lateral hooked bristles. The removal of the polar lobe during first cleavage does not have a great effect on development. These lobeless embryos display a normal pattern of cleavages through the time of mesentoblast formation. The resulting larvae are essentially normal, however they do not form functional photocytes. If the CD cell is isolated after the removal of the first polar lobe, the resulting larva is virtually identical to those formed by the intact CD cell except it lacks the photocyte cells. These results indicate that two separate pathways are involved in the segregation of developmental or morphogenetic potential which takes place during first cleavage. One set of factors, which are necessary for photocyte formation, are associated with the first polar lobe. Other factors that are necessary for the formation of the eyes and lateral hooked bristles are segregated by the unequal cleavage which results from an internal shifting of the cleavage spindle. The removal of a large portion of the vegetal region of the embryo during first cleavage leads to the production of larvae which display a decreased ability to form eyes and lateral hooked bristles. These embryos frequently display an abnormal pattern of cleavages. They do not form the primary somatoblast or the mesentoblast. These results indicate that the vegetal region of the CD cell of Chætopterus is analogous to polar lobes which have been studied in other species, and is therefore important in the specification of the D quadrant. These features of the first cleavage of Chætopterus are a combination of those displayed by forms with direct unequal cleavage and other forms which cleave unequally through the production of large polar lobes. The significance of these findings is discussed relative to the origins of these different types of unequal cleavage.     

Relationship Between Spatial Pattern of Basal Bodies and Membrane Skeleton (Epiplasm) During the Cell Cycle of Tetrahymena: cdaA Mutant and Anti-Membrane Skeleton Immunostaining

Microtubular basal bodies and epiplasm (membrane skeleton) are the main components of the cortical skeleton of Tetrahymena. The aim of this report was to study functional interactions of basal bodies and epiplasm during the cell cycle. The cortex of Tetrahymena cells was stained with anti-epiplasm antibody. This staining produced a bright epiplasmic layer with a dark pattern of unstained microtubular structures. The fluorescence of the anti-epiplasm antibody disappeared at sites of newly formed microtubular structures, so the new basal body domains and epiplasmic layer could be followed throughout the cell cycle. Different patterns of deployment of new basal bodies were observed in early and advanced dividers. In advanced dividers the fluorescence of the epiplasmic layer diminished locally within the forming fission line where the polymerization of new basal bodies largely extincted. In wild type Tetrahymena, the completion of the micronuclear metaphase/anaphase transition was associated with a transition from the pattern of new basal body deployment and epiplasm staining of the early divider to the pattern of the advanced dividers. The signal for the fission line formation in Tetrahymena (absent in cdaA1 Tetrahymena mutationally arrested in cytokinesis) brings about 1) transition of patterns of deployment of basal bodies and epiplasmic layer on both sides of the fission line; and 2) coordination of cortical divisional morphogenesis with the micronuclear mitotic cycle.     

The occurrence of multinucleate giant cells in yeasts

Summary The spontaneous occurrence of giant cells has been observed in young cultures ofLipomyces lipofer and three different genotypes ofSaccharomyces. Stained preparations of all abnormal cultures revealed that the giant cells characteristically contained more than one nucleus, the number ranging from one to six. In both genera the phenomenon was found to be transient, for rapidlygrowing cultures arising from isolated giant cells reverted, at varying rates, to populations of small uninucleate cells which appeared normal in all respects.     

Guanylate requirement for patterning the postcephalic body region of the brine shrimp Artemia

Mycophenolic acid (MA) reduces growth and survival rates of Artemia larvae fed hypoxanthine. The inhibitory effect of MA is suppressed by dietary guanosine as expected for inosinate dehydrogenase inhibition. Pulse MA treatments lasting 24 h imposed on larvae from 24 to 96 h posthatch result in the production of abnormal adults with thoracic, genital or abdominal defects. The MA-induced anomalies are interpreted as a disruption of pattern formation. Since dietary guanosine restores normal pattern in adults developing from larvae, MA-treated during early stages, it is concluded that guanylate production is required at critical developmental times to establish normal developmental fates.     

Mitochondrial Associations with Specific Components of the Cortex of Tetrahymena thermophila Nanney & McCoy, 1976: Microtubules and the Epiplasm1

Ultrastructural observations of the cortically-located mitochondria of Tetrahymena thermophila revealed associations not only between the mitochondria and certain of the cortical microtubule bands, but also between the mitochondria and the epiplasm of the cortex. Most of the distal mitochondrial surface is close and parallel to the epiplasm; favorable views show bridge-like structures spanning the 20–10 nm gap between the mitochondrion and the epiplasm. Previous studies have shown that the placement of mitochondria in the cortex appears to be determined by certain of the cortical microtubule bands. This study, however, shows that mitochondrion-microtubule interactions account for only a small proportion of the total mitochondrial area associated with the cortex; the rest is accounted for by the epiplasm. A possible analogue of the spectrin layer of erythrocyte membranes, the epiplasm may be important in helping to arrange the intricately organized components of the ciliate cortex. Its involvement in apparently helping to “moor” mitochondria to their cortical sites is the first suggestion of any role in cell patterning played by the epiplasm.     

Early Morphogenesis of Glugea-lnduced Xenomas in Laboratory-Reared Flounder

Glugea stephani-infecled submucosal cells of laboratory-reared winter flounder, Pseudopleuronectes americanus, change to unique giant cell xenomas. These cells hypertrophy while the intracellular Glugea propagate to high numbers in the cytoplasm and eventually overrun the host cell. The xenomas slowly reach 20-25 muml;m (at 17°C) by day 10 after parasite invasion. These xenomas (eight often examined by electron microscopy) are coated with a mucus-like envelope onto which is attached a layer of endothelial ceils. The 10-day xenomas display (a) host cell endonuclear polyploidization and amitosis, (b) limited parasite growth and reproduction, and (c) a host cell cytoplasm structure similar to that seen in undifferentiated phagocytes. Glugea parasites do not induce obvious cell degenerative effects in 10-day xenomas; the 20-day xenomas are hypertrophied to 70-100 m?m. These cells are characterized by (a) a host cell component denuded of endoplasmic reticulum and phagosome membrane, (b) a reduction in host cell ribosomes and the disappearance of host cell cytoskeletal assemblages, including microtubules, and (c) a significant increase in vegetative Glugea within xenomas. Evidence indicates cytoplasmic calcium of the host cell xenoma is perturbed by the intracellular Glugea; the alterations in the host cell calcium domains may be a big factor in the induction of the block of mitosis in the host cell and in the disruption in its cytoskeletal controls.     

Impaired adult myeloid progenitor CMP and GMP cell function in conditional c-myb-knockout mice

The differentiation of myeloid progenitors to mature, terminally differentiated cells is a highly regulated process. Here, we showed that conditional disruption of the c-myb proto-oncogene in adult mice resulted in dramatic reductions in CMP, GMP and MEP myeloid progenitors, leading to a reduction of neutrophils, basophils, monocytes and platelets in peripheral blood. In addition, c-myb plays a critical role at multiple stages of myeloid development, from multipotent CMP and bipotent GMP to unipotent CFU-G and CFU-M progenitor cells. c-myb controls the differentiation of these cells and is required for the proper commitment, maturation and normal differentiation of CMPs and GMPs. Specifically, c-myb regulates the precise commitment to the megakaryocytic and granulo-monocytic pathways and governs the granulocytic-monocytic lineage choice. c-myb is also required for the commitment along the granulocytic pathway for early myeloid progenitor cells and for the maturation of committed precursor cells along this pathway. On the other hand, disruption of the c-myb gene favors the commitment to the monocytic lineage, although monocytic development was abnormal with cells appearing more mature with atypical CD41 surface markers. These results demonstrate that c-myb plays a pivotal role in the regulation of multiple stages in adult myelogenesis.     

Consequences of disrupting the gene that encodes α-glucosidase II in the N-linked oligosaccharide biosynthesis pathway of Dictyostelium discoideum

We have identified and disrupted the gene coding for α-glucosidase II in Dictyostelium discoideum. This enzyme is responsible for removing two α1,3-linked glucose residues from N-linked oligosaccharides on newly synthesized glycoproteins. Mutagenesis by restriction enzyme-mediated integration (REMI) generated a clone, DG1033, which grows well but forms abnormal fruiting bodies with short, thick stalks. The strain lacks α-glucosidase II activity and makes incompletely processed N-linked oligosaccharides that are abnormally large and have fewer sulfate and phosphate esters. The morphological, enzymatic, and oligosaccharide profile phenotypes of the disruption mutant are all recapitulated by a targeted disruption of the normal gene. Furthermore, all of these defects are corrected in cells transformed with a normal, full-length copy of the gene. The phenotypic characteristics of DG1033 as well as chromosomal mapping of the disrupted gene indicate that it is the site of the previously characterized modA mutation. The Dictyostelium gene is highly homologous to α-glucosidase II genes in the human and the pig, C. elegans, and yeast. Although various cell lines have been reported to be defective in α-glucosidase II activity, disruption of the Dictyostelium gene gives the first example of a clear developmental phenotype associated with loss of this enzyme. Dev. Genet. 21:177–186, 1997. © 1997 Wiley-Liss, Inc.     

Lgl1 deficiency disrupts hippocampal development and impairs cognitive performance in mice

Cellular polarity is crucial for brain development and morphogenesis. Lethal giant larvae 1 (Lgl1) plays a crucial role in the establishment of cell polarity from Drosophila to mammalian cells. Previous studies have found the importance of Lgl1 in the development of cerebellar, olfactory bulb, and cerebral cortex. However, the role of Lgl1 in hippocampal development during the embryonic stage and function in adult mice is still unknown. In our study, we created Lgl1‐deficient hippocampus mice by using Emx1‐Cre mice. Histological analysis showed that the Emx1‐Lgl1^?/? mice exhibited reduced size of the hippocampus with severe malformations of hippocampal cytoarchitecture. These defects mainly originated from the disrupted hippocampal neuroepithelium, including increased cell proliferation, abnormal interkinetic nuclear migration, reduced differentiation, increased apoptosis, gradual disruption of adherens junctions, and abnormal neuronal migration. The radial glial scaffold was disorganized in the Lgl1‐deficient hippocampus. Thus, Lgl1 plays a distinct role in hippocampal neurogenesis. In addition, the Emx1‐Lgl1^?/? mice displayed impaired behavioral performance in the Morris water maze and fear conditioning test.     

DEVELOPMENTAL GENETICS IN BARLEY: A MUTANT FOR STOMATAL DEVELOPMENT

The barley mutants eceriferum-g, which have wax deficiencies in several organs, show an abnormal stomatal development as a pleiotropic effect. The main abnormalities are double and triple stomatal complexes. Minor alterations are present as extra cells that alter the normal sequence of the stomatal row and abnormal subsidiary cells that are either larger, smaller, or displaced from their normal position. These characteristics are present in the 12 independently isolated mutants of the g locus, but could not be found in any of the other eceriferum mutants studied. The morphogenetic origin and a developmental sequence for the abnormalities are postulated.     

Haemocyte involvement in the repair of the insect central nervous system after selective glial disruption

Summary Injection of physiologically inert particles (fluorescent microspheres) has a profound effect on neural repair of central nervous connectives of the cockroach Periplaneta americana following selective glial disruption. The injected particles, which do not gain direct access to the central nervous tissues, are taken up by a relatively small proportion (< 10%) of the haemocytes. This interference with haemocyte function virtually abolishes the appearance of the granule-containing cells (which are prominently involved in normal glial repair) and produces abnormal reorganization of the superficial glial elements. These results are interpreted as evidence that the granule-containing cells are derived from haemocytes which are critically involved in glial repair.     

Nocturnal predation of king penguins by giant petrels on the Crozet Islands

Dietary segregation of sympatric seabirds in the Southern Ocean is partly linked to differences in their foraging techniques. We have investigated the activity of giant petrels (Macronectes spp.) in a king penguin (Aptenodytes patagonicus) colony day and night during the austral winter of 2001 on the Crozet Islands. Using an automatic identification system and an infrared video camera, we followed 15 petrels tagged with micro transponders. Our data show that giant petrels predate king penguin chicks during the night. The activity of giant petrels is even slightly higher during nighttime than during the day. In addition, our data show a higher nocturnal activity by northern giant petrels (M. halli) than by southern giant petrels (M. giganteus). These unexpected results raise questions concerning visual adaptations to nocturnal foraging in giant petrels and their potential impact on the sleep, vigilance and crèching behavior of penguin chicks.     

Role of the MT-MTOC complex in determination of the cellular locomotory unit inDictyostelium

Summary The microtubule inhibitors, ethyl-N-phenylcarbamate (EPC) and thiabendazole (TB), which disrupt cytoplasmic microtubules and induce giant cells inDictyostelium (Kitanishi et al. 1984), were found to induce the occurrence of multiple microtubule organizing centers (MTOCs) in these giant cells. Probing was done by indirect immunofluorescence using monoclonal anti--tubulin. The nuclear DNA content of the giant cells increased in parallel with an increase in the number of MTOCs, as shown by microspectrophotometory of cells stained with the fluorescent DNA stain DAPI (4,6-diamidino-2-phenylindole).Shortly after the inhibitors were removed, the MTOCs of the giant cell formed multiple mitotic spindles or synchronously reconstituted numerous cytoplasmic MT-networks. These events apparently reflected the cell-cycle dependent activities of the MTOCs at the time the inhibitors were removed. When multiple spindles were formed, numerous cytoplasmic MT-networks became organized subsequent to the breakdown of the spindles. In either case, reconstitution of the cytoplasmic MT-networks was followed by apparently normal cytokinesis resulting in the production of many daughter cells each containing a single MT-MTOC complex. The evidence suggested the possible mechanism of the induction of multiple MTOCs, and implied that the MT-MTOC complex is significant in the cytokinesis ofDictyostelium by determining the cell locomotory unit.     

How did bacterial ancestors reproduce? Lessons from L‐form cells and giant lipid vesicles

In possible scenarios on the origin of life, protocells represent the precursors of the first living cells. To study such hypothetical protocells, giant vesicles are being widely used as a simple model. Lipid vesicles can undergo complex morphological changes enabling self‐reproduction such as growth, fission, and extra‐ and intravesicular budding. These properties of vesicular systems may in some way reflect the mechanism of reproduction used by protocells. Moreover, remarkable similarities exist between the morphological changes observed in giant vesicles and bacterial L‐form cells, which represent bacteria that have lost their rigid cell wall, but retain the ability to reproduce. L‐forms feature a dismantled cellular structure and are unable to carry out classical binary fission. We propose that the striking similarities in morphological transitions of L‐forms and giant lipid vesicles may provide insights into primitive reproductive mechanisms and contribute to a better understanding of the origin and evolution of mechanisms of cell reproduction. Editor's suggested further reading in BioEssays Synthesizing artificial cells from giant unilamellar vesicles: State‐of‐the art in the development of microfluidic technology Abstract     

The differentiation of monocytes into macrophages,epithelioid cells,and multinucleated giant cells in subcutaneous granulomas

The morphological changes occurring in monocytes during their differentiation into macrophages, epithelioid cells, Langhans-type giant cells, and foreign-body-type giant cells were investigated in foreign-body granulomas induced by subcutaneous implantation of pieces of Melinex plastic. Analysis based on Adams's (1974) criteria for discrimination between the several types of cell of the monocyte line, showed that each type has a characteristic type of granule. Primary and secondary granules, numerous in the Golgi area of monocytes were generally found close to the cell membrane and decreased in number in maturing macrophages. This was accompanied by an increase in the number of microtubules. Mature macrophages show numerous characteristic macrophage granules, which are round (average diameter: 280 nm) and have a halo between the limiting membrane and granular matrix. Mature epithelioid cells have characteristic epithelioid cell granules, and multinucleated giant cells a heterogenous population of granules. Fusing macrophages generally have their Golgi areas facing each other, and also show a reduced thickness of the cell coat. The morphology of the multinucleated giant cell is closely related to the number of nuclei present. In Langhans-type giant cells, which generally have two to ten nuclei, a giant centrosphere with numerous aggregated centrioles is found. In transition forms between Langhans-type and foreign-body-type giant cells, which generally contain 10--30 nuclei, the centrioles show less aggregation. In the foreign-body-type giant cells, which generally have more than 30 nuclei, centrioles are virtually absent and never aggregated. These differences between the Langhans-type giant cells, the foreign-body-type giant cells, and the transition forms, support our previous finding that Langhans-type giant cells are the precursors of foreign-body-type giant cells.     

An unstable giant satellite associated with chromosomes 21 and 22 in the same individual.

The short arms of the acrocentric chromosomes are among the most common sites in which to find human chromosomal heteromorphisms. Heteromorphic chromosomes are noted for their variability between individuals and populations; however, they generally are consistent within an individual. Contrary to this general rule, a normal female was found to have a giant satellite on the short arm of a chromosome 22 in most lymphocytes and fibroblasts, but in other cells, it was attached to a chromosome 21. Furthermore, in some cells, it was found on multiple chromosomes, that is, on both 22's or on a 21 and a 22. The familial nature of this heteromorphism was established when it was found in the woman's mother, where it was confined exclusively to chromosome 22. These results suggest an unstable giant satellite associated with both G-group chromosomes of a normal individual. Results are discussed in the light of the patient's occupational exposure to insecticides at a mushroom farm.     

Absence of alterations in antigenic determinats inSalmonella typhimurium after mecillinam-induced morphological changes

Oval forms ofSalmonella typhimurium resulting from exposure to mecillinam demonstrated electrophoretic differences in the intracellular soluble proteins as compared to the normal organisms. No differences were found, however, in the electrophoretic patterns of cell wall protein.Salmonella rods, or oval forms stained with specific fluorescein-coupled antibodies raised in rabbits against normal or mecillinam-induced abnormal forms, showed identical patterns of fluorescence. Identical lines of precipitins in Ouchterlony system were produced between any combination of antibodies and cytosol protein from normal or mecillinam-exposedSalmonella or with cell wall extracts of either forms. These results indicated that the induced ovoid transformation produced by mecillinam is not accompanied by any demonstrable alterations in the antigenic determinants ofS. typhimurium.