bluuebunny/crossref_metadata_2025 huggingface dataset:
feh-1 and apl-1, the Caenorhabditis elegansorthologues of mammalian Fe65 and β-amyloid precursor protein genes, are involved in the same pathway that controls nematode pharyngeal pumping
Authors: Zambrano Nicola , Bimonte Marida , Arbucci Salvatore , Gianni Davide , Russo Tommaso , Bazzicalupo Paolo
Published: April 2021

The multigenic family of mammalian Fe65s encodes three highly similar proteins with the same modular organisation: a WW domain and two phosphotyrosine-binding domains. The PTB2 domain of these proteins binds to the cytosolic domains of the Alzheimer's β-amyloid precursor protein APP and related proteins APLP1 and APLP2, generating a highly redundant system that is hard to dissect by reverse genetics. By searching potential Fe65-like genes in the nematode Caenorhabditis elegans, we identified a single gene, feh-1 (Fe65 homolog-1), encoding a protein with a high sequence similarity to mammalian Fe65s. FEH-1 is also functionally related to mammalian orthologues;in fact its PTB2 domain binds to APL-1, the product of the C. elegansorthologue of APP. Staining with specific antibodies show that the neuromuscular structures of the pharynx are the sites in which FEH-1 is present at highest levels. Expression studies with reporters indicate that the feh-1 gene is also expressed by a subset of the worm neurons.

We generated and isolated a deletion allele of feh-1, and the corresponding homozygous mutants arrest as late embryos or as L1 larvae,demonstrating for the first time an essential role for a Fe65-like gene in vivo. The pharynx of homozygous larvae does not contract and the worms cannot feed. Analysis of pharyngeal pumping in heterozygous worms and in feh-1 RNA-interfered worms indicates that dosage of feh-1function affects the rate of pharyngeal contraction in C. elegans. Interference with apl-1 double-stranded RNA showed a similar effect on pharyngeal pumping, suggesting that FEH-1 and APL-1 are involved in the same pathway. The non-redundant system of the nematode will prove useful for studying the basic biology of the Fe65-APP interaction and the molecular events regulated by this evolutionarily conserved system of interacting proteins.
Filopodia are conduits for melanosome transfer to keratinocytes
Authors: Scott Glynis , Leopardi Sonya , Printup Stacey , Madden Brian C.
Published: April 2021

Melanosomes are specialized melanin-synthesizing organelles critical for photoprotection in the skin. Melanosome transfer to keratinocytes, which involves whole organelle donation to another cell, is a unique biological process and is poorly understood. Time-lapse digital movies and electron microscopy show that filopodia from melanocyte dendrites serve as conduits for melanosome transfer to keratinocytes. Cdc42, a small GTP-binding protein, is known to mediate filopodia formation. Melanosome-enriched fractions isolated from human melanocytes expressed the Cdc42 effector proteins PAK1 and N-WASP by western blotting. Expression of constitutively active Cdc42(Cdc42V12) in melanocytes co-cultured with keratinocytes induced a highly dendritic phenotype with extensive contacts between melanocytes and keratinocytes through filopodia, many of which contained melanosomes. These results suggest a unique role for filopodia in organelle transport and, in combination with our previous work showing the presence of SNARE proteins and rab3a on melanosomes, suggest a novel model system for melanosome transfer to keratinocytes.
Low-energy laser irradiation promotes the survival and cell cycle entry of skeletal muscle satellite cells
Authors: Shefer Gavriella , Partridge Terry A. , Heslop Louise , Gross Jacqueline G. , Oron Uri , Halevy Orna
Published: April 2021

Low energy laser irradiation (LELI) has been shown to promote skeletal muscle cell activation and proliferation in primary cultures of satellite cells as well as in myogenic cell lines. Here, we have extended these studies to isolated myofibers. These constitute the minimum viable functional unit of the skeletal muscle, thus providing a close model of in vivo regeneration of muscle tissue. We show that LELI stimulates cell cycle entry and the accumulation of satellite cells around isolated single fibers grown under serum-free conditions and that these effects act synergistically with the addition of serum. Moreover, for the first time we show that LELI promotes the survival of fibers and their adjacent cells, as well as cultured myogenic cells, under serum-free conditions that normally lead to apoptosis. In both systems, expression of the anti-apoptotic protein Bcl-2 was markedly increased, whereas expression of the pro-apoptotic protein BAX was reduced. In culture, these changes were accompanied by a reduction in the expression of p53 and the cyclin-dependent kinase inhibitor p21, reflecting the small decrease in viable cells 24 hours after irradiation. These findings implicate regulation of these factors as part of the protective role of LELI against apoptosis. Taken together, our findings are of critical importance in attempts to improve muscle regeneration following injury.
Quantitation and functional characterization of neural cells derived from ES cells using nestin enhancer-mediated targeting in vitro
Authors: Lenka Nibedita , Lu Zhong J. , Sasse Philipp , Hescheler Jürgen , Fleischmann Bernd K.
Published: April 2021

To gain insight into early events of neurogenesis, transgenic embryonic stem (ES) cells were generated using the enhanced green fluorescence protein(EGFP) reporter gene under the regulatory control of the neural stem cell marker, nestin. The expression of EGFP in undifferentiated ES cells suggested that the onset of endogenous nestin occurred before neurulation. Upon differentiation of ES cells, the EGFP expression became confined to the neural lineage and asynchrony in ES-cell-derived neural differentiation was evident. The EGFP intensity was prominent in the proliferative progenitors and unipolar neurons, whereas downregulation occurred in differentiating bi- and multipolar neurons. This was corroborated quantitatively using flow cytometry where maximal generation of neural progenitors was observed 4-12 days post-plating. The proliferative potential of neural progenitors as well as glia, in contrast to post-mitotic neurons,was also evident by time-lapse microscopy. The functional characterization of progenitors revealed an absence of voltage-activated inward currents, whereas the Na+ current (INa) was detected prior to Ca2+ currents (ICa) in differentiating neurons. Additionally, inhibitory receptor-operated channels could be detected at these early stages of development in bi- and multipolar neurons suggesting that the pre-committed progenitors had retained their intrinsic ability to give rise to functional neurons. This study sheds new light on early events of neurogenesis defining the quantitative and qualitative aspects and demarcating the functional neural cell types from ES cells in vitro.
Vascular endothelial cells that express dystroglycan are involved in angiogenesis
Authors: Hosokawa Hiroshi , Ninomiya Haruaki , Kitamura Yukisato , Fujiwara Keigi , Masaki Tomoh
Published: April 2021

We have earlier shown that dystroglycan (DG) is a lamininbinding protein and as such is a cell adhesion molecule. DG is a heterodimer of α andβ DG subunits. β-dystroglycan (βDG) is the membrane spanning subunit, whereas the α subunit is bound to the extracellular domain ofβDG. To study physiological function of the protein, we expressed full-length DG (FL-DG) and the cytoplasmic domain of βDG(ΔβDG) in bovine aortic endothelial cells (BAE) and examined their effects on cell adhesion, migration, proliferation and tube formation. FL-DG enhanced adhesion of BAE to laminin-1, whereas ΔβDG inhibited it. Cell migration was inhibited by overexpressing ΔβDG in these cells,although it was not affected by FL-DG overexpression. In a proliferation assay, FL-DG decreased the growth rate, and it also caused cells to extensively spread. ΔβDG caused opposite effects; it increased the growth rate and reduced the cell surface area. In a tube formation assay on Matrigel, FL-DG caused an obvious inhibition, whereas ΔβDG accelerated tube formation. These results suggest a potential role of endothelial dystroglycan in the control of angiogenesis. Anti-βDG immunohistochemistry indicated increased expression of DG in vascular endothelial cells within malignant tumors. By contrast, the antibody failed to stain endothelial cells in normal tissues. In cultured BAE, the level ofβDG was low in serum-deprived quiescent cells and was upregulated in proliferating cells. Our results suggest that the expression of DG in endothelial cells is under a dynamic regulation and may play a role in angiogenesis.
Analysis ofChlamydomonasSF-assemblin by GFP tagging and expression of antisense constructs
Authors: Lechtreck Karl-Ferdinand , Rostmann Jutta , Grunow Andrea
Published: April 2021

Striated fiber assemblin (SF-assemblin or SFA) is the major component of the striated microtubule-associated fibers (SMAFs) in the flagellar basal apparatus of green flagellates. We generated nuclear transformants of Chlamydomonas expressing green fluorescent protein (GFP) fused to the C-terminus of SFA. SFA-GFP assembled into striated fibers that exceeded those of wild-type cells in size by several fold. At elevated temperatures(≥32°C) SFA-GFP was mostly soluble and heat shock depolymerized the SMAFs. C-terminal deletions of 18 or only six residues disturbed the ability of SFA-GFP to polymerize, indicating an important role of the C-terminal domain for fiber formation. The exchange of the penultimate Ser275 with alanine made SFA-GFP highly insoluble, causing aberrant fiber formation and conferring heat stability to the fibers. By contrast, a replacement with glutamic acid increased the solubilty of the molecule, indicating that phosphorylation on Ser275 might control solubility of SFA. In vivo observation of GFP fluorescence showed that SFA-GFP fibers were disassembled during mitosis. In cells overexpressing full-length or truncated SFA-GFP, the amount of wild-type protein was reduced. Elevated temperatures dissolved SFA-GFP fibers and induced the synthesis of SFA, suggesting that cells control both the amount of soluble and polymeric SFA. By expressing constructs consisting of cDNA and genomic DNA for parts of SFA in antiparallel configuration, the amount of SFA was severely reduced. In these strains we observed defects in flagellar assembly, indicating an important role for noncontractile striated roots in the flagella apparatus.
Partner telomeres during anaphase in crane-fly spermatocytes are connected by an elastic tether that exerts a backward force and resists poleward motion
Authors: LaFountain James R. , Cole Richard W. , Rieder Conly L.
Published: April 2021

As chromosomes move polewards during anaphase in crane-fly spermatocytes,trailing arms commonly stretch backwards for a brief time, as if tethered to their partners. To test that notion, a laser microbeam was used to sever trailing arms and thereby release telomere-containing arm segments (called acentric fragments because they lack kinetochores) from segregating chromosomes. Analysis of the movement of acentric fragments after their release provided clear evidence that previously conjoined partners were indeed tethered at their telomeres and that tethers exerted backward forces that were sufficient to move the fragment across the equator and into the opposite half-spindle. To address concerns that tethers might be artifacts of in vitro cell culture, spermatocytes were fixed in situ, and stretched arms within fixed cells provided strong evidence for tethers in vivo. The substantial resistance that tethers impose on the poleward movement of chromosomes must normally be over-ridden by the poleward `pulling' forces exerted at kinetochores. In spermatocytes, poleward forces are supplied primarily by the`traction fibers' that are firmly attached to kinetochores through end-on attachments to the plus ends of kinetochore microtubules.
Control of localization of a spindle checkpoint protein, Mad2, in fission yeast
Authors: Ikui Amy E. , Furuya Kanji , Yanagida Mitsuhiro , Matsumoto Tomohiro
Published: April 2021

To ensure accurate chromosome segregation, the spindle checkpoint delays the onset of sister chromatid separation when the spindle is not attached to a kinetochore. Mad2, a component of the checkpoint, targets fission yeast Slp1/budding yeast Cdc20/human p55CDC and prevents it from promoting proteolysis, which is a prerequisite to sister chromatid separation. The protein is localized to unattached kinetochores in higher eukaryotes, and it is thought to be required for activation of the checkpoint as well. In this study, Mad2 and its target Slp1 were visualized in a tractable organism,fission yeast Schizosaccharomyces pombe. When cells were arrested at a prometaphase-like stage, the Mad2-Slp1 complex was stable and the two proteins were colocalized to unattached kinetochores. When the spindle attachment was completed, the complex was no longer detectable and only Mad2 was found associated to the spindle. These results would suggest that unattached kinetochores provide sites for assembly of the Mad2-Slp1 complex. During interphase, Mad2 was localized to the nuclear periphery as well as to the chromatin domain. This localization was abolished in a yeast strain lacking Mad1, a protein that physically interacts with Mad2. Mad1 may anchor Mad2 to the nuclear membrane and regulate its entry into the nucleus.
Light saturation of growth and photosynthesis of the shade plant Marchantia Polymorpha
Authors: Mache R. , Loiseaux S.
Published: April 2021

The growth rate of the shade plant Marchantia was at its maximum for a low illumination, 2–3 × 103 lx, and was inhibited by an excess of light.

Photosynthesis by intact thalli and by isolated chloroplasts of Marchantia was saturated by a light intensity of 2–3 × 103 lx. These isolated chloroplasts were able to carry on satisfactory rates of photosynthesis, up to 35 μM CO 2 /h/mg chlorophyll.

The Hill reaction and photosystem II were also saturated by the same light intensities, demonstrating that the factor limiting the light saturation of photosynthesis is located in the chloroplast. The structure of chloroplasts was strongly modified by an excess of light, small grana and fret membranes being replaced by continuous grana.
Panoramic views of cells in tissue culture using an orbiting chamber
Authors: Hlinka J. , Sanders F. K.
Published: April 2021

A new method has been developed for observing single, or small groups, of cells at an angle that can be varied from 0 to 360 °. A better understanding can thus be achieved of cell/cell and cell/substrate interactions during locomotion, adhesion and, especially, emperipolesis and phagocytosis.
Erythropoiesis in the newt, Triturus Cristatus laur. : I. identification of the ‘erythroid precursor cell’
Authors: Grasso J. A.
Published: April 2021

Phenylhydrazine injection in salamanders (Triturus sp.) produces a complete loss of all erythrocytes and haemoglobin but does not result in an immediate erythropoietic response. Splenectomized newts survive absence of the erythron most readily. At 11–14 days after injection, the peripheral blood contains numerous, primitive cells which exhibit large, leptochromatic nuclei, wide variation in cytoplasmic basophilia, and variation in cell size. These cells constitute a spectrum of cells collectively called ‘erythroid precursor cells’ (EPC) which terminate in the formation of basophilic erythroblasts. Earlier cell forms (at 11 days) contain few cytoplasmic ribosomes and few organelles but the ribosome concentration gradually increases, as does a fibrillogranular precipitate presumed to be associated with haemoglobin synthesis. Metabolically, these cells are engaged in proliferation, RNA, haem, and protein synthesis. Erythroid precursor cells, which comprise 50–60% of the total blood cell population at 11–14 days, are replaced by basophilic erythroblasts at 15–18 days. The morphological and metabolic properties of these cells are compatible with their role in red blood cell formation. However, their similarity to mammalian marrow ‘transitional’ cells and the occurrence of similar cells in association with macrophages suggest possible differentiative potencies along several cell lines. While little is known about the origin of erythroid precursor cells, preliminary experiments suggest that they may be derived from circulating lymphocytes.
Ultrastructural and cytochemical features of mammalian skeletal muscle fibres following denervation
Authors: Gauthier Geraldine F. , Dunn Rosemary A.
Published: April 2021

After denervation, the usual cytochemical criteria for identifying fibre types in mammalian skeletal muscle are lost, and thus ultrastructural analysis becomes essential. The width of the Z-line is a valuable criterion for the identification of fibre types in normal muscle, and the differences in width remain apparent even after denervation. In the red portion of the normal rat semitendinosus muscle, there is a mixture of red, intermediate and white fibres. The red fibre has the highest mitochondrial content and the widest Z-line, whereas the white fibre has the lowest mitochondrial content and the narrowest Z-line (about half as wide as that of the red fibre). The intermediate fibre is intermediate in both characteristics. At 14 days after denervation, there is a shift toward a more homogeneous population of fibres, which are rich in mitochondria, but which have an ultrastructural appearance distinct from that of normal fibres. Most of the fibres resemble normal red or intermediate fibres, but lack the characteristic subsarcolemmal aggregations of mitochondria. There are also some fibres which exhibit severe myofibrillar disruption. These have narrow Z-lines, and are therefore classified as white fibres. This suggests that there is a preferential alteration of white fibres, and that their degradation may be responsible for the apparent increase in the proportion of red or intermediate fibres at this stage of denervation. In these disrupted fibres the sarcoplasmic membrane systems lose their usual organization, and triads become aligned parallel to the longitudinal axis of the myofibrils. All fibres, therefore, are, to some extent, altered by denervation, though the changes differ according to the type of fibre.

In normal fibres, ribosomes are sparse, but following denervation they are abundant, particularly at the periphery. This is a general response to removal of the nerve supply, and does not appear to be related to fibre type; but it is more apparent in red and intermediate fibres, which possess an extensive superficial sarcoplasm. Conspicuous aggregations of large mitochondria normally occur in the subsarcolemmal region of these fibres, but after denervation, there are, instead, massive accumulations of free ribosomes and a few cisternae of roughsurfaced endoplasmic reticulum. Our observations suggest, moreover, that this concentration of protein-synthetic machinery corresponds to a spread in the sensitivity to acetylcholine along the surface of the fibres.
Abolition by myosin and heavy meromyosin of the inhibitory effect of smooth-muscle actomyosin antibodies on cell aggregation In Vitro
Authors: Kemp R. B. , Jones B. M. , Gröschel-Stewart U.
Published: April 2021

The ability of anti-chicken smooth-muscle actomyosin γ-globulins (anti-GAM) to inhibit the aggregation of dissociated cells from the skeletal muscle and liver of chick embryos was abolished by pretreatment of the anti-GAM with either myosin or heavy meromyosin (HMM). When the same cells were treated with HMM at a concentration of 1 mg per 2×10’ cells/ml Eagle’s MEM they aggregated as readily as untreated cells.

The negative electrophoretic mobility of the embryonic chick fibroblastic cells was significantly reduced by the globulin fraction of anti-GAM but not of HMM-treated anti-GAM or non-immunized rabbit serum. Anti-chicken striated muscle actomyosin γ-globulins slightly reduced negative mobility but HMM had no effect.

The experiments show that the inhibitory effect on cell aggregation of anti-GAM preparations is produced by the anti-myosin antibodies. They also provide support for the theory that a surface-localized myosin-like protein has a regulatory function in cell adhesion.
The mammalian intervertebral disk: Fibrous structures of the whale nucleus pulposus
Authors: Ludowieg J. J. , Parker J.
Published: April 2021

Striated fibres showing a beaded appearance in the electron microscope were prepared from the insoluble collagen residue of foetal nucleus pulposus. The assembling and stability of the beaded fibres are controlled to a significant degree by electrostatic forces. In acid solutions (pH 2·0) the organization of the structures is preserved. Analytical data on the preparations show the presence of proteoglycans containing chondroitin sulphate and keratan sulphate, as well as collagen.
Contractile filamentous material in the pillar cells of fish gills
Authors: Bettex-Galland M. , Hughes G. M.
Published: April 2021

The secondary lamellae of the gill filaments are the sites of gas exchange in fish gills. They are mainly composed of 2 epithelial sheets joined together by pillar cells. These cells are characterized by collagen columns contained in infoldings of the cell membrane and oriented perpendicular to the epithelial sheets. The gill is the first organ to which the blood flows from the heart and within the secondary lamellae it flows through channels between the pillar cells.

The presence in the pillar cells of fine cytoplasmic filaments situated parallel to the collagen columns has now been observed in many fishes and the hypothesis has been advanced that they constitute a contractile system.

This paper describes how gill filaments were treated in a way similar to that used for other non-muscular cells in order to demonstrate in situ the presence of contractile proteins of the actomyosin type. Gill filaments were extracted in glycerol-containing solutions of low ionic strength, and then incubated with and without ATP. After incubation with ATP examination in the electron microscope showed that in the vicinity of the collagen columns, the pillar cells contain clusters of disordered thin filaments intermingled with spindle-shaped needles. This structure is characteristic of muscle actomyosin, as well as actomyosin-like proteins extracted from cells of non-muscular origin and fixed in a contracted state. It is deduced that the thin cytoplasmic filaments surrounding the collagen columns consist of an actomyosin-like con-tractile protein. On incubation of extracted gill filaments without ATP, the expected negativeresult was obtained, i.e. the filaments retain their orientation parallel to the columns. The function of the contractile filaments within the pillar cells is discussed in relation to the control of blood flow through the secondary lamellae and the reduction of pressure drop during the flow of blood across the gills of fish.
Factors determining the site of synthesis of poliovirus proteins: The early attachment of virus particles to endoplasmic membranes
Authors: Fenwick M. L. , Wall Margaret J.
Published: April 2021

Cytoplasmic extracts of HeLa cells made 1 to 2 h after infection with radioactive poliovirus contained 150-s virus particles and 130-s, perhaps partially disrupted, particles. The latter were resistant to RNase but sensitive to dodecylsulphate. Both particles were associated with fast sedimenting material from which they could be released by deoxycholate, but not by EDTA. In isopyenic gradients of sucrose in D2O the labelled particles formed a sharp band coincident with membrane-bound ribosomes at a density of 1·23 g cm”3. It is suggested that attachment of virus particles to endoplasmic reticulum may be an early stage in the infectious cycle, determining the site of subsequent steps.

The inhibition of cellular protein synthesis that develops during infection affects membrane-bound as well as free polysomes and therefore does not determine the membrane-association of viral protein synthesis.
Some aspects of remyelination after demyelination produced by the intraneural injection of lysophosphatidyl choline
Authors: Hall Susan M.
Published: April 2021

The morphology of remyelination following demyelination induced by the intraneural injection of lysophosphatidyl choline, LPC, has been examined in the mouse sciatic nerve, at periods up to 240 days post-injection. It was found that, in many fibres, the process resembled primary myelinogenesis. There was a moderate Schwann cell proliferation; those Schwann cells not involved in remyelination remained closely associated with the remyelinating Schwann cell/axon unit, within a common basal lamina tube. Numerous small axons, considered to be sprouts from the remyelinating axon, were observed lying in contact with the ‘supernumerary Schwann cells’.

In a small population of fibres, however, atypical morphological features were consistently seen: (i) multiple mesaxons, indicating probable remyelination by tunication; (ii) paranodal reorganization in the junctional zone; (iii) the formation of internodal ‘pseudonodes’, which subsequently underwent transition into incisures of Schmidt-Lanterman.

These structures are discussed in terms of the re-establishment of the Schwann cell/axon relationship.
Electron-microscopic observations on the macronuclear development of Stylonychia Mytilus and Tetrahymena Pyriformis (Ciliophora-Protozoa)
Authors: Murti K. G.
Published: April 2021

This report describes an ultrastructural investigation of macronuclear development follow-ing conjugation in Stylonycltia mytilus (a spirotrichous ciliate) and Tetrahymena pyriformis (a holotrichous ciliate).

In S. mytilus, polytene chromosomes are formed in the young macronucleus (macronuclear Anlage). They are subsequently broken between the bands by ‘membranous’ partitions; the assembly of the membranes appears to be concomitant with the formation of the polytene chromosomes. The membranes in the Anlage appear to originate from fibrous material seen in the early Anlage. This fibrous material in the earlier stages is seen concentrated at several points along the border of the inner nuclear membrane. In the later stages it is seen in the interior of the Anlage, outlining the developing polytene chromosomes. As the chromosomes reach the maximum degree of polyteny, the fibrous material condenses to acquire a mem-branous appearance and extends into the interband regions. The Anlage throughout this period shows a progressive increase in size.

Subsequently, the membranes enclose individually each band plus portions of the 2 adjacent interband regions of the polytene chromosomes to form a large number of vesicles. After vesicle formation the Anlage shrinks, and the chromatin inside the vesicles shows degradative changes. Finally, the vesicles disappear, the membrane degradation products appear at the nuclear membrane, and the Anlage now contains nucleoli. The Anlage increases its DNA content by multiple roundsof replication to become a mature macronucleus. The ultra-structural changes observed in the Anlage support the idea of genetic diminution (i.e. extensive DNA synthesis, elimination of many DNA nucleotide sequences, and amplification of the remaining DNA nucleotide sequences in a second period of DNA synthesis) proposed earlier on the basis of cytochemical, biochemical, and limited electron-microscope studies.

In T. pyriformis, the macronuclear development differs substantially from that of Stylonychia. Features such as the formation and degradation of polytene chromosomes are absent in the macronuclear development of Tetrahymena; the young macronucleus in this cell becomes a mature macronucleus by progressive increment in size and chromatin content with no apparent genetic diminution. These observations agree with cytochemical studies on the macronuclear development of Tetrahymena.
Timing of the first cleavage division of haploid mouse eggs, and the duration of its component stages
Authors: Kaufman M. H.
Published: April 2021

Mouse eggs were activated by treatment with hyaluronidase which removed the follicle cells, followed by culture in vitro, and examined at the first cleavage mitosis. Second polar body extrusion usually occurred and haploid parthenogenesis was initiated. Air-dried chromosome preparations were made between 11 and 15·5 h after activation. Out of the 308 eggs examined 74 had already progressed to the 2-cell stage; the remaining 234 at the 1-cell stage were examined in detail. All chromosome preparations of the first cleavage mitosis were classified into groups corresponding with the stages of prometaphase, metaphase (early or ‘pre-chromatid’, ‘chromatid’ and ‘late chromatid’) and anaphase.

An indirect estimate was made of the duration of the first cleavage mitosis and of its com-ponent stages from the incidence of stages observed at different time intervals after activation. Similar eggs were also observed at 37 °C by time-lapse cine-photography and the interval between the disappearance of the pronucleus to the beginning of telophase of the first cleavage division was determined. The results of timing studies on the haploid eggs were compared with results obtained from similar observations on the first cleavage division of fertilized eggs which would of course normally be diploid.

Artificially activated eggs with2 pronuclei, resulting from second polar body suppression, were also examined, and serial chromosome preparations during mitosis showed that the 2 pronuclear chromosome groups unite on the first cleavage spindle and divide to give a hetero-zygous diploid 2-cell embryo.
Cyclic membrane flow in the ingestive-digestive system of peritrich protozoans ii. cup-shaped coated vesicles
Authors: Mckanna J. A.
Published: April 2021

As peritrich food vacuoles condense during the initial stage of digestion, excess membrane pinches off as cup-shaped vesicles which exhibit a structured coat on the non-cytoplasmic surface of the membrane. As the membrane cycles from cup-shaped vesicles to diskoidal vesicles to cytopharynx to food vacuoles, the coat undergoes structural transformations from the condensed form (5×16 nm peg-shaped elements) to an extended form (long thin filaments). Review of the literature reveals morphologically similar coats which undergo similar transformations in the digestive organelles of flagellate protozoa, Hydra absorptive cells, insect pericardial cells, ileal absorptive cells of suckling rats, cells of the guinea-pig placenta, mammalian Langerhans cells, and macrophages. The similar functional situation in which these coated membranes occur suggests that the coat is important to the recognition and binding of macromolecules.
Change in surface extensibility ofFundulusdeep cells during early development
Authors: Tickle Cheryll A. , Trinkaus J. P.
Published: April 2021

The extensibility of the periphery of the deep cells of the Fundulus blastoderm was investigated by applying negative pressure to the cell surface in culture by means of a micropipette. The relative negative pressure required to produce standard deformations of the surface was measured for cells from embryos in 2 different stages of development. Less negative pressure was required to deform cells from early gastrulae than cells from early blastulae. This finding correlates with the behaviour of deep cells in vivo-, early blastula cells are rounded, form blebs, and do not engage in locomotion, whereas early gastrula cells form extended lobopodia and lamellipodia and engage actively in locomotion.
The patterned organization of thick and thin microfilaments in the contracting pseudopod of Difflugia
Authors: Eckert B. S. , Mcgee-Russell S. M.
Published: April 2021

The lobopodial pseudopods of the shelled amoeba Difflugia undergo a rapid active contraction and length shortening which results in movement of the organism, or rapid pseudopod retraction. In polarized light, the pseudopod shows high birefringence before and during this normal contraction, suggesting a high degree of linear organization, and a complex pattern of changes. Immediately conventional fixation begins, pseudopods retract rapidly, and show changes in birefringence. When longitudinal sections are viewed in the electron microscope, such fixed, contracting pseudopods are seen to contain thick (14–16 nm) and thin (5–8 nm) microfilaments. Montages demonstrate that these microfilaments are found in close parallel association with each other, and lie parallel and peripheral to the longitudinal axis of the pseudopod, which is the axis of contraction. This distribution suggests that the patterned microfilaments could be involved in the shortening process and that they could account for the birefringence seen in the contracting pseudopod. Rapid alignment, or assembly, is also suggested.
A possible function of microtubules suggested by their abnormal distribution in rubbery wood
Authors: Nelmes Brenda J. , Preston R. D. , Ashworth Denise
Published: April 2021

A difference in the distribution of microtubules in the peripheral cytoplasm of developing fibres has been observed between normal apple wood and that infected with ‘rubbery wood’ disease. In normal wood, where microtubules are abundant, the fibre wall is lignified, compact in texture and of limited thickness. In rubbery wood, where there are fewer microtubules, lignification is not complete in the fibre wall, which has a coarse, loose texture, and is abnormally thick. The whole stem is highly flexible. The pit membrane, which is unlignified in both normal and rubbery wood, has no microtubules adjacent to the plasmalemma.

It is suggested that microtubules are concerned in channelling into the wall substances, such as lignin precursors, which are essential for certain steps in the polymerization of the amorphous component of the wall.
Changes in structure of the disks of retinal rods in hypotonic solutions
Authors: Falk Gertrude , Fatt P.
Published: April 2021

Changes in isolated frog rod outer segments, suspended in hypotonic solutions, have been examined by light and electron microscopy. Swelling of the disk occurs in hypotonic solutions. When one half or more NaCl is omitted from the Ringer solution used for suspending the rod outer segments, swelling is accompanied by the appearance of localized, irregular expansions projecting as buds from the disks. The axes of the buds tend to be in the plane of the disk, as can be seen in cross-sections of outer segments. In longitudinal sections of outer segments, the sectioned buds have profiles which were previously interpreted as vesicles. Attention is drawn to the properties of the disk edge, among which is a resistance to extension.
Dna replication in the chromosomes of the chicken, Gallus Domesticus
Authors: Mcfarlane Pamela W. , Callan H. G.
Published: April 2021

DNA fibre autoradiography has been used to study the replication of chromosomal DNA from chicken cells in tissue culture at 37 °C. The S-phase is estimated to be about 7·5 h. Replication proceeds in the manner first described by Huberman & Riggs. Tandemly arranged units replicate bi-directionally from fork-like growing points, the times of initiation of individual repheating sections being staggered. Evidence against the existence of defined termini is presented. The rate of replication in these chicken cells is some 25–30 μm/h one-way. The mean interval between adjacent initiation points for replication is 63 μm, with a range of some 25–145 μm. Although initiation intervals vary in length, neighbouring intervals tend to be similar in length.
Proliferating hybrid cells formed between rat spermatids and an established line of mouse fibroblasts
Authors: Nyormoi Okot , Coon H. G. , Sinclair J. H.
Published: April 2021

Proliferating hybrids were formed between rat spermatids and LM(TK−) cl 1 D, an established line of mouse fibroblasts. Spermatids were obtained from dissociated rat seminiferous tubules by differential attachment of testicular somatic cells to culture plates, followed by gravity velocity sedimentation into linear Ficoll gradients. Cells were fused with the aid of Sendai virus and hybrid selection was facilitated by the inability of cl 1 D cells to grow in HAT medium and the inability of spermatids to attach or proliferate in vitro. Three types of cells grew in fusion plates: (1) unfused contaminant rat testicular somatic cells; (2) rat testicular cell × cl 1 D hybrids and (3) rat spermatid × cl 1 D hybrids. Unfused rat testicular somatic cells were morphologically and karyologically different from either type of hybrid. The 2 hybrid classes were distinguished by the total number of chromosomes and the number of parental chromosome markers. Rat chromosomes are preferentially eliminated from haploid as well as diploid hybrids and at least 3 rat enzymes (lactate dehydrogenase, glucose phosphate isomerase and an unknown oxidase) are synthesized in hybrid clones of both types. The implications of partial haploid hybrids for genetic analysis are briefly discussed.
Sensitivity of the cell division cycle to α-amanitin in Allium root tips
Authors: De La Torre C. , Fernandez-Gomez M. E. , Gimenez-Martin G. , Gonzalez-Fernandez A.
Published: April 2021

The effect of α-amanitin on the cell cycle in Allium cepa meristematic cells was studied: the G1 and G2 periods are prolonged respectively to 1·9 and 1·7 times the normal duration; the S-period is lengthened very little; and the prophase of mitosis is increased to twice the normal duration. It is postulated that real differences in the activity of the non-nucleolar RNA polymerase might exist in the course of the cell division cycle and that they would account for the higher sensitivities shown by G1, G2 and prophase.

On the other hand, the interphase nucleolus responds by segregation in the first few hours of α-amanitin treatment, but recovers its normal structure in continued presence of the drug; and nucleolar reorganization is inhibited in the first few hours in recently formed cells, but the process is subsequently speeded up to attain the same value 4 h after the treatment was begun as in untreated cells.
Arrangement of subunits in flagellar microtubules
Authors: Amos Linda A. , Klug A.
Published: April 2021

Electron micrographs of outer doublet tubules from flagella have been analysed by methods which make use of the computed diffraction patterns of electron-microscope images. Analysis of singlet A-tubules in the tips of flagella has led to a determination of the helical surface lattice of the A-subfibre, confirming that there are 13 longitudinal protofilaments in the tubule wall and that dimers in neighbouring protofilaments form a staggered arrangement, equivalent to the lattice with an axial periodicity of 8 · 0 nm predicted in earlier work. A low-resolution 3-dimensional image of the A-tubule has been reconstructed, which supports the evidence for an 8 · 0-nm-long heterodimer oriented along the protofilaments. The heterodimer is identified as a pair of 4 · 0-nm morphological units, which appear to be globular at this resolution.

Filtered images have been obtained from doublet tubules which show that the B-subfibre is also made up of 8 · 0-nm dimers, but it differs from the A-tubule in that dimers in adjacent filaments are not in a staggered arrangement but are lined up obliquely at a shallow angle. Using the additional information about the hands of the lattices in the 2 subfibres which is presented in the accompanying paper, a model for the whole doublet has been proposed.
The hands of helical lattices in flagellar doublet microtubules
Authors: Linck R. W. , Amos Linda A.
Published: April 2021

Negatively stained arrays of flagellar doublet microtubules have been tilted about an axis perpendicular to the tubule axes and imaged at angles of ± 20°. The images have been filtered to enhance the 4-nm periodicities in the tubulin lattice, and the resulting filtered images interpreted by comparison with simulated projections of tilted helical lattices. The different appearances of the edges of filtered doublet tubules for positive and negative tilt angles suggest that the 4-nm lattices of both subfibres are of the same hand, with the 3-start helices in each being left-handed. The information has been incorporated in a model proposed for the arrangement of subunits in doublet microtubules, which is described in the preceding paper.
An electron-microscope study of cell deletion in the anuran tadpole tail during spontaneous metamorphosis with special reference to apoptosis of striated muscle fibres
Authors: Kerr J. F. R. , Harmon B. , Searle J.
Published: April 2021

The mechanism, of cell deletion responsible for involution of the anuran tadpole tail during spontaneous metamorphosis was studied by light and electron microscopy, attention being focused on epidermis and striated muscle.

The earliest indication of pending dissolution of epidermal cells was found to be aggregation of condensed chromatin beneath the nuclear envelope. This is followed by breaking up of the nucleus, and cytoplasmic condensation and budding with the production of a number of compact, membrane-bounded cell fragments with relatively well preserved organelles. These are then ingested and degraded by nearby viable cells, the majority by distinctive macrophage-like cells, which are scattered throughout the epidermis, and a few by epithelial cells. The morphological changes observed in the dying epidermal cells are the same as those described both in the ‘programmed cell death’ that plays an important role in the normal development of vertebrate embryos and in the type of cell death that has been shown to be involved in regulating the size of tissues in adult mammals under normal as well as pathological conditions; it has been suggested elsewhere that apoptosis might be a suitable name for the phenomenon.

Deletion of striated muscle fibres in the tadpole tail is accomplished by a process that appears to be a modification of classical apoptosis, in which dilatation and confluence of elements of the sarcoplasmic reticulum lead to internal fragmentation, the usual surface budding presumably being precluded by the large volume and specialized structure of these cells. The early and late nuclear changes, and the apparent ultrastructural integrity of organelles in the membrane-bounded muscle fragments are typical of apoptosis, and subsequent degradation within macrophages follows the standard stereotyped pattern. An essentially similar process has been described by others in the muscles of metamorphosing insect larvae, but whether striated muscle cells in adult higher vertebrates can undergo apoptosis is still uncertain.
The membranes of the basal labyrinth in kidney cells of the stickleback, Gasterosteus aculeatus, studied in ultrathin sections and freeze-etch replicas
Authors: Wendelaar Bonga S. E. , Veenhuis M.
Published: April 2021

The structure of the basal labyrinth in kidney cells of freshwater sticklebacks was studied in ultrathin sections (after fixation with permanganate, osmium tetroxide, and combinations of glutaraldehyde with osmium tetroxide) and in freeze-etch replicas (after pretreatment with glutaraldehyde and/or glycerol, or without pretreatment). The structure of the basal labyrinth in sticklebacks, and probably in other teleost species, differs essentially from the type of labyrinth found in kidney cells of mammals like the rat. In the latter animals, the space enclosed by the membranes of the labyrinth is intercellular. In the stickleback the labyrinth consists of an intracellular system of branched membranes lining narrow saccular spaces. These spaces communicate with the exterior of the cells by means of small pores, located in the lateral and basal parts of the outer cell membranes.

All chemical fixation procedures used introduced specific structural artifacts. It is concluded that the structure of the basal labyrinth is relatively well preserved after fixation with potassium permanganate, with a mixture of glutaraldehyde and osmium tetroxide, or with osmium tetroxide when applied for 10 min only. The unit-membrane structure was, however, absent after all procedures involving osmium tetroxide.

In freeze-etch replicas determinations were made of the numbers of small particles covering the surfaces and fracture faces of the membranes of the basal labyrinth and of the outer cell membranes. The numbers per unit area of surface proved to be markedly constant and specific for each of the four faces of both types of membranes. Specific differences were found between the particle densities of the outer cell membranes and the membranes of the basal labyrinth. This finding points to functional differences between these types of membranes.

Particle densities were not influenced by pre-incubation with glycerol. After fixation with glutaraldehyde, the particles adhering to the outer and inner surfaces had decreased in number.

It is concluded from this study that membrane structure, as revealed in thin sections as well as in freeze-etch replicas, is consistent with Singer’s ‘fluid lipid-crystal protein’ model.
Growth and differentiation of the golgi apparatus in the red alga,Callithamnion roseum
Authors: Hawkins Eva Konrad
Published: April 2021

The fine structure of the Golgi apparatus during development of tetrasporangia of Calli-thamnion roseum is described. Dictyosomes and associated vesicles of 4 developmental stages of sporangia are examined. The wall of sporangia exhibits a heretofore unseen cuticle in red algae. Development of the spore wall and a new plasma membrane around spores occurs through fusion of adjacent Golgi vesicles along the periphery of cells. Observations are discussed in relation to wall formation and expansion of tetrads and in comparison with other work on growth and differentiation of the Golgi apparatus.
Growth of human diploid fibroblasts in media with different amino acid composition
Authors: Litwin J.
Published: April 2021

Human embryonic diploid lung fibroblasts were capable of growing in a medium consisting of Eagle’s MEM vitamins plus 0·1 μg/ml biotin, Earle’s salt solution, 4 mM glutamine, 0·4 mM cystine, 0·5 mM tyrosine, 10 % undialysed calf serum and 1 mM pyruvate. The growth rate and percent cell attachment in this medium was slightly less than in Eagle’s MEM but the longevity was about the same. Addition of 0· 5–1·0 mM histidine stimulated growth but addition of 0· 2 mM phenylalanine, methionine or valine decreased longevity markedly.

Maintaining a constant pH of about 7·5–7·6 with 20 mM of the organic buffers HEPES, TES or TRICINE yielded a growth rate equal to or better than that of cells growing in unbuffered medium. Some buffers gave good growth initially but eventually the longevity decreased (20mM BIS-TRIS, 20 mM BICINE, 10 mM TRIS). In almost all cases the initial exposure to the buffers yielded the best growth results.
Continuous nucleolar dna synthesis in late-interphase nuclei of Physarum polycephalum after transplantation into postmitotic plasmodia
Authors: Guttes E.
Published: April 2021

In the myxomycete, Physarum polycephalum, nuclear DNA synthesis commences immediately upon completion of mitosis. While the synthesis of extranucleolar DNA is completed within a few hours, nucleolar DNA synthesis occurs during most of the S-phase and the entire G2 phase of the intermitotic period. When large (polyploid), late-interphase nuclei were allowed to bypass mitosis by transplantation into recipient plasmodia which were at early interphase and which belonged to a strain having smaller nuclei, the nucleolar DNA of the transplanted nuclei continued to be labelled (autoradiographs) after incubation of the host plasmodia with [3H] thymidine until they entered prophase along with the nuclei of the host plasmodium, approximately one intermitotic period later. This labelling was DNase-sensitive and RNase-resistant. When late-interphase nuclei were labelled with [3H]thymidine just prior to transplantation, there was no decrease of label after transplantation during the additional intermitotic period. We conclude from these experiments that there is no obligatory alternation between nucleolar DNA duplication and mitosis in Physarum polycephalum and that nucleolar DNA replication might exhibit amplification during an experimentally prolonged intermitotic period.