bluuebunny/crossref_metadata_2025 huggingface dataset:
How nematode sperm crawl
Authors: Bottino Dean , Mogilner Alexander , Roberts Tom , Stewart Murray , Oster George
Published: April 2021

Sperm of the nematode, Ascaris suum, crawl using lamellipodial protrusion, adhesion and retraction, a process analogous to the amoeboid motility of other eukaryotic cells. However, rather than employing an actin cytoskeleton to generate locomotion, nematode sperm use the major sperm protein (MSP). Moreover, nematode sperm lack detectable molecular motors or the battery of actin-binding proteins that characterize actin-based motility. The Ascaris system provides a simple ‘stripped down’ version of a crawling cell in which to examine the basic mechanism of cell locomotion independently of other cellular functions that involve the cytoskeleton. Here we present a mechanochemical analysis of crawling in Ascaris sperm. We construct a finite element model wherein (a) localized filament polymerization and bundling generate the force for lamellipodial extension and (b) energy stored in the gel formed from the filament bundles at the leading edge is subsequently used to produce the contraction that pulls the rear of the cell forward. The model reproduces the major features of crawling sperm and provides a framework in which amoeboid cell motility can be analyzed. Although the model refers primarily to the locomotion of nematode sperm, it has important implications for the mechanics of actin-based cell motility.

Movies available on-line.
Characterization of temperature-sensitive mutations in the yeast syntaxin 1 homologues Sso1p and Sso2p, and evidence of a distinct function for Sso1p in sporulation
Authors: Jäntti Jussi , Aalto Markku K. , Öyen Mattias , Sundqvist Lena , Keränen Sirkka , Ronne Hans
Published: April 2021

The duplicated genes SSO1 and SSO2 encode yeast homologues of syntaxin 1 and perform an essential function during fusion of secretory vesicles at the plasma membrane. We have used in vitro mutagenesis to obtain a temperature-sensitive SSO2 allele, sso2-1, in which a conserved arginine has been changed to a lysine. A yeast strain that lacks SSO1 and carries the sso2-1 allele ceases growth and accumulates secretory vesicles at the restrictive temperature. Interestingly, the strain also has a pronounced phenotype at the permissive temperature, causing a defect in bud neck closure that prevents separation of mother and daughter cells. The same mutation was introduced into SSO1, producing the sso1-1 allele, which also has a temperature-sensitive phenotype, although less pronounced than sso2-1. A screen for high copy number suppressors of sso2-1 yielded three genes that are involved in the terminal step of secretion: SNC1, SNC2 and SEC9. The sso1-1 mutation interacts synthetically with a disruption of the MSO1 gene, which encodes a Sec1p interacting protein. Interestingly, we further found that both MSO1 and SSO1, but not SSO2, are required for sporulation. This difference is not due to differential expression, since SSO2 expressed from the SSO1 promoter failed to restore sporulation. We conclude that a functional difference exists between the Sso1 and Sso2 proteins, with the former being specifically required during sporulation.
Proprotein convertases are important mediators of the adipocyte differentiation of mouse 3T3-L1 cells
Authors: Croissandeau Gilles , Basak Ajoy , Seidah Nabil G. , Chrétien Michel , Mbikay Majambu
Published: April 2021

Mouse 3T3-L1 cells are widely used to study adipocyte differentiation in vitro. When treated with insulin, dexamethasone and isobutylmethylxanthine these fibroblastic cells differentiate into round triglyceride-rich adipocytes. Because several proteins implicated in adipocyte differentiation(e.g. type 1 IGF receptors) are proteolytically activated by endoproteinases of the proprotein convertase family, we sought to determine whether these endoproteinases are crucial for adipose conversion. In this study, we show that expression of the proprotein convertases PACE4, PC7 and furin increases when 3T3-L1 cells are induced to differentiate into adipocytes. The differentiation was blocked in transfected cells expressingα1-antitrypsin Portland or in normal cells pre-treated with the synthetic inhibitor decanoyl-RVKR-chloromethylketone. Both inhibitors are known to specifically inactivate proprotein convertases. The block was associated with impaired proteolytic activation of proIGF-1 receptor, absence of induction of the adipogenic transcriptional factor PPARγ and marked reduction of the nuclear translocation of the C/EBPβ factor. Taken together, these data constitute evidence that proprotein convertases are crucial mediators of adipogenesis.
Chromosome associations in budding yeast caused by integrated tandemly repeated transgenes
Authors: Fuchs Jörg , Lorenz Alexander , Loidl Josef
Published: April 2021

The binding of GFP-tagged tetracycline repressor (TetR) molecules to chromosomally integrated tetracycline operator (tetO) sequence repeats has been used as a system to study chromosome behaviour microscopically in vivo. We found that these integrated transgenes influence the architecture of yeast interphase nuclei, as chromosomal loci with tandem repeats of exogenous tetO sequences are frequently associated. These associations occur only if TetR molecules are present. tetO tandem repeats associate regardless of their chromosomal context. When they are present at a proximal and a distal chromosomal position, they perturb the normal polarized Rabl-arrangement of chromosome arms by recruiting chromosome ends to the centromeric pole of the nucleus. Associations are established at G1 and are reduced during S-phase and mitosis. This system may serve as a model for the role of DNA sequence-specific binding proteins in imposing nonrandom distribution of chromosomes within the nucleus.
CEACAM1 isoforms with different cytoplasmic domains show different localization, organization and adhesive properties in polarized epithelial cells
Authors: Sundberg Ulla , Öbrink Björn
Published: April 2021

CEACAM1 is a signaling cell adhesion molecule expressed in epithelia,vessel endothelia and leukocytes. It is expressed as two major isoforms with different cytoplasmic domains. CEACAM1 occurs both in cell-cell contact areas and on apical surfaces of polarized epithelial cells, but it is not known how the different isoforms are distributed in polarized cells or what the functions of CEACAM1 are in the apical surfaces. We investigated the localization and organization of the two CEACAM1 isoforms in transfected,polarized MDCK cells by confocal microscopy and differential surface labelling. CEACAM1-L was found on both the apical and the lateral surfaces,whereas CEACAM1-S appeared exclusively on the apical surfaces. Maintenance of the lateral localization of CEACAM1-L required homophilic binding between CEACAM1-L molecules on adjacent cells. Double-labelling with anti-CEACAM1 antibodies directed against different epitopes indicated that apical CEACAM1-L occurred either in a homophilic adhesive state or in a free non-adhesive state. CEACAM1-S appeared almost exclusively in the homophilic adhesive state. These findings suggest that CEACAM1 mediates adhesive bonds between adjacent microvilli on the apical surfaces.
p65-NFκB synergizes with Notch to activate transcription by triggering cytoplasmic translocation of the nuclear receptor corepressor N-CoR
Authors: Espinosa Lluís , Santos Sara , Inglés-Esteve Julia , Muñoz-Canoves Pura , Bigas Anna
Published: April 2021

Notch/RBP-Jκ and nuclear factor-κB (NFκB) complexes are key mediators of the progression of many cellular events through the activation of specific target gene transcription. Independent observations have shown that activation of Notch-dependent transcription generally correlates with inhibition of differentiation. In contrast, activated NFκB complexes are required for progression of differentiation in several systems. Although some interactions between both pathways have been observed, the physiological significance of their connection is unclear. We have now demonstrated that the increase in p65-NFκB protein levels enhances Notch-mediated activation of the Hes1 promoter up to three-fold. This effect does not require NFκB transcriptional activity, and it is independent of the previously described interaction between Notch and p50-NFκB. Furthermore, we show that p65-NFκB can modulate subcellular localization of the transcriptional corepressor N-CoR, abrogating N-CoR mediated repression of the Hes1 promoter. In addition, p65-NFκB is able to upregulate not only the Hes1 but also other promoters containing SRE and AP-1 sites, which are repressed by N-CoR. Thus, we conclude that p65-NFκB can regulate gene expression by a general mechanism that involves cytoplasmic translocation of the transcriptional corepressor protein N-CoR.
Different mechanisms of cell polarisation in vegetative and shmooing growth in fission yeast
Authors: Niccoli Teresa , Nurse Paul
Published: April 2021

Schizosaccharomyces pombe cells have two polarised growth modes:an intrinsic vegetative growth mode, determined by an internal positioning mechanism and an extrinsic shmooing growth mode, activated by external pheromone. We have analysed the role of the cell end marker Tea1p, the CLIP170 like protein Tip1p, the kinesin like protein Tea2p and the Dyrk-like kinase Pom1p, during the switch between the two growth patterns, with the intention of studying the switch away from the vegetative growth mode. In vegetative growth these morphological factors are concentrated at cell ends, whereas during shmooing growth they are delocalised from the cell ends. In the absence of Tea1p, Tip1p and Tea2p, vegetative cells display microtubule and cell polarisation defects, but shmooing cells are indistinguishable from wild-type and shmoo more readily. These results suggest that Tea1p, Tip1p and Tea2p are not required for polarised growth during shmooing, but form part of the intrinsic vegetative growth mode that needs to be dismantled before cells can generate an extrinsic growth patterns. In contrast, Pom1p appears to have a role in the initial stages of the switch to the shmooing growth mode.
Sla1p couples the yeast endocytic machinery to proteins regulating actin dynamics
Authors: Warren Derek T. , Andrews Paul D. , Gourlay Campbell W. , Ayscough Kathryn R.
Published: April 2021

Sla1p is a protein required for cortical actin patch structure and organisation in budding yeast. Here we use a combination of immunofluorescence microscopy and biochemical approaches to demonstrate interactions of Sla1p both with proteins regulating actin dynamics and with proteins required for endocytosis. Using Sla1p-binding studies we reveal association of Sla1p with two proteins known to be important for activation of the Arp2/3 complex in yeast, Abp1p and the yeast WASP homologue Las17p/Bee1p. A recent report of Sla1p association with Pan1p puts Sla1p in the currently unique position of being the only yeast protein known to interact with all three known Arp2/3-activating proteins in yeast. Localisation of Sla1p at the cell cortex is, however, dependent on the EH-domain-containing protein End3p, which is part of the yeast endocytic machinery. Using spectral variants of GFP on Sla1p(YFP) and on Abp1p (CFP) we show for the first time that these proteins can exist in discrete complexes at the cell cortex. However, the detection of a significant FRET signal means that these proteins also come close together in a single complex, and it is in this larger complex that we propose that Sla1p binding to Abp1p and Las17p/Bee1p is able to link actin dynamics to the endocytic machinery. Finally, we demonstrate marked defects in both fluid-phase and receptor-mediated endocytosis in cells that do not express SLA1, indicating that Sla1p is central to the requirement in yeast to couple endocytosis with the actin cytoskeleton.
TheFA2gene ofChlamydomonasencodes a NIMA family kinase with roles in cell cycle progression and microtubule severing during deflagellation
Authors: Mahjoub Moe R. , Montpetit Ben , Zhao Lifan , Finst Rip J. , Goh Benjamin , Kim Apollos C. , Quarmby Lynne M.
Published: April 2021

The NIMA kinases are one of several families of kinases that participate in driving the eukaryotic cell cycle. NIMA-related kinases have been implicated in G2/M progression, chromatin condensation and regulation of the centrosome cycle. Here we report the identification of a new member of this family, FA2, from Chlamydomonas reinhardtii. FA2 was originally discovered in a genetic screen for deflagellation-defective mutants. We have previously shown that FA2 is essential for basal-body/centriole-associated microtubule severing. We now report that the FA2 NIMA-related kinase also plays a role in cell cycle progression in Chlamydomonas. This is the first indication that members of the NIMA family might exert their effects through the regulation of microtubule severing.
Loss of Heterochromatin Protein 1 (HP1) chromodomain function in mammalian cells by intracellular antibodies causes cell death
Authors: Filesi Ilaria , Cardinale Alessio , van der Sar Sjaak , Cowell Ian G. , Singh Prim B. , Biocca Silvia
Published: April 2021

The chromodomain (CD) is a highly conserved motif present in a variety of animal and plant proteins, and its probable role is to assemble a variety of macromolecular complexes in chromatin. The importance of the CD to the survival of mammalian cells has been tested. Accordingly, we have ablated CD function using two single-chain intracellular Fv (scFv) fragments directed against non-overlapping epitopes within the HP1 CD motif. The scFv fragments can recognize both CD motifs of HP1 and Polycomb (Pc) in vitro and, when expressed intracellularly, interact with and dislodge the HP1 protein(s) from their heterochromatin localization in vivo. Mouse and human fibroblasts expressing anti-chromodomain scFv fragments show a cell-lethal phenotype and an apoptotic morphology becomes apparent soon after transfection. The mechanism of cell death appears to be p53 independent, and the cells are only partly rescued by incubation with the wide spectrum caspase inhibitor Z-VAD fmk. We conclude that expression of anti-chromodomain intracellular antibodies is sufficient to trigger a p53-independent apoptotic pathway that is only partly dependent on the known Z-VAD-inhibitable caspases, suggesting that CD function is essential for cell survival.
CEP110 and ninein are located in a specific domain of the centrosome associated with centrosome maturation
Authors: Ou Young Y. , Mack Gary J. , Zhang Meifeng , Rattner Jerome B.
Published: April 2021

The mammalian centrosome consists of a pair of centrioles surrounded by pericentriolar material (PCM). The architecture and composition of the centrosome, especially the PCM, changes during the cell cycle. Recently, a subset of PCM proteins have been shown to be arranged in a tubular conformation with an open and a closed end within the centrosome. The presence of such a specific configuration can be used as a landmark for mapping proteins in both a spatial and a temporal fashion. Such mapping studies can provide information about centrosome organization, protein dynamics,protein-protein interactions as well as protein function. In this study, the centrosomal proteins CEP110 and ninein were mapped in relationship to the tubular configuration. Both proteins were found to exhibit a similar distribution pattern. In the mother centrosome, they were found at both ends of the centrosome tube, including the site of centrosome duplication. However,in the daughter centrosome they were present only at the closed end. At the closed end of the mother and daughter centrosome tube, both CEP110 and ninein co-localized with the centriolar protein CEP250/c-Nap1, which confirms ninein's centriole association and places CEP110 in association with this structure. Importantly, the appearance of CEP110 and ninein at the open end of the daughter centrosome occurred during the telophase-G1 transition of the next cell cycle, concomitant with the maturation of the daughter centrosome into a mother centrosome. Microinjection of antibodies against either CEP110 or ninein into metaphase HeLa cells disrupted the reformation of the tubular conformation of proteins within the centrosome following cell division and consequently led to dispersal of centrosomal material throughout the cytosol. Further, microinjection of antibodies to either CEP110 or ninein into metaphase PtK2 cells not only disrupted the tubular configuration within the centrosome but also affected the centrosome's ability to function as a microtubule organizing center (MTOC). This MTOC function was also disrupted when the antibodies were injected into postmitotic cells. Taken together, our results indicate that: (1) a population of CEP110 and ninein is located in a specific domain within the centrosome, which corresponds to the open end of the centrosome tube and is the site of protein addition associated with maturation of a daughter centrosome into a mother centrosome; and (2) the addition of CEP110 and ninein are essential for the reformation of specific aspects of the interphase centrosome architecture following mitosis as well as being required for the centrosome to function as a MTOC.
TheDrosophilagap junction channel geneinnexin 2controls foregut development in response to Wingless signalling
Authors: Bauer Reinhard , Lehmann Corinna , Fuss Bernhard , Eckardt Franka , Hoch Michael
Published: April 2021

In invertebrates, the direct communication of neighbouring cells is mediated by gap junctions, which are composed of oligomers of the innexin family of transmembrane proteins. Studies of the few known innexinmutants in Drosophila and C. elegans have shown that innexin proteins, which are structurally analogous to the connexins in vertebrates,play a major structural role as gap junctional core components in electric signal transmission. We show that Drosophila innexin 2 mutants display a feeding defect that originates from a failure of epithelial cells to migrate and invaginate during proventriculus organogenesis. The proventriculus is a valve-like organ that regulates food passage from the foregut into the midgut. Immunhistological studies indicate that innexin 2 is functionally required to establish a primordial structure of the proventriculus, the keyhole, during the regionalisation of the embryonic foregut tube, which is under the control of Wingless and Hedgehog signalling. Our genetic lack- and gain-of-function studies, and experiments in Dorsophila tissue culture cells provide strong evidence that innexin 2 is a target gene of Wingless signalling in the proventricular cells. This is the first evidence, to our knowledge, that an invertebrate gap junction gene controls epithelial tissue and organ morphogenesis in response to the conserved WNT signalling cascade.
Leukotriene D4 activates MAPK through a Ras-independent but PKCϵ-dependent pathway in intestinal epithelial cells
Authors: Paruchuri Sailaja , Hallberg Bengt , Juhas Maria , Larsson Christer , Sjölander Anita
Published: April 2021

We have recently shown that leukotriene D4 (LTD4)increases cell survival in intestinal epithelial cells. Here we report and explore the complementary finding that LTD4 also enhances proliferation in these cells. This proliferative response was approximately half of that induced by epidermal growth factor (EGF) and its required activation of protein kinase C (PKC), Ras and the mitogen-activated protein kinase (MAPK) Erk-1/2. EGF also activated Erk-1/2 in these cells; however the EGF-receptor inhibitor PD153035 did not affect the LTD4-induced activation of Erk-1/2. In addition, LTD4 did not induce phosphorylation of the EGF receptor, nor did pertussis toxin (PTX) block EGF-induced activation of Erk-1/2, thus refuting a possible crosstalk between the receptors. Furthermore, LTD4-induced, but not EGF-induced,activation of Erk-1/2 was sensitive to PTX, PKC inhibitors and downregulation of PKCϵ. A definite role for PKCϵ in LTD4-induced stimulation of Erk-1/2 was documented by the inability of LTD4 to activate Erk-1/2 in cells transfected with either the regulatory domain of PKCϵ (an isoform specific dominant-negative inhibitor) or a kinase-dead PKCϵ. Although Ras and Raf-1 were both transiently activated by LTD4, only Raf-1 activation was abolished by abrogation of the PKC signal. Furthermore, the LTD4-induced activation of Erk-1/2 was unaffected by transfection with dominant-negative N17 Ras but blocked by transfection with kinase-dead Raf-1. Consequently, LTD4 regulates the proliferative response by a distinct Ras-independent, PKCϵ-dependent activation of Erk-1/2 and a parallel Ras-dependent signaling pathway.
Characterization of rat TOM70 as a receptor of the preprotein translocase of the mitochondrial outer membrane
Authors: Suzuki Hiroyuki , Maeda Maki , Mihara Katsuyoshi
Published: April 2021

We cloned a ∼70 kDa rat mitochondrial outer membrane protein (OM70)with a sequence identity of 28.1% and 20.1% with N. crassa and S. cerevisiae Tom70, respectively. Even with this low sequence identity,however, the proteins share a remarkable structural similarity: they have 7-10 tetratricopeptide repeat motifs and are anchored to the outer membrane through the N-terminal transmembrane domain with the bulk portion located in the cytosol. Antibodies against OM70 inhibited import of preproteins, such as the ADP/ATP carrier and rTOM40, that use internal targeting signals but not the import of cleavable presequence-containing preproteins. Blue native gel electrophoresis and immunoprecipitation of digitoninsolubilized mitochondrial outer membranes revealed that OM70 was loosely associated with the ∼400 kDa translocase complex of the mitochondrial outer membrane, which contains rTOM22 and rTOM40. A yeast two-hybrid system demonstrated that OM70 interacted with rTOM20 and rTOM22 through the cytoplasmic domains. Thus, OM70 is a functional homologue of fungal Tom70 and functions as a receptor of the preprotein import machinery of the rat mitochondrial outer membrane. Furthermore, the N-terminal 66 residue region of OM70, which comprises a hydrophilic 41 residue N-terminal domain, a 22 residue transmembrane domain and three arginine residues, is sufficient to act as a mitochondria-targeting signal, and the arginine cluster is crucial for this function.
Activation of SGK1 by HGF, Rac1 and integrin-mediated cell adhesion in MDCK cells: PI-3K-dependent and -independent pathways
Authors: Shelly Candace , Herrera Roman
Published: April 2021

The SGK1 protein belongs to the AGC gene family of kinases that are regulated by phosphorylation mediated by PDK1. SGK1 regulation is accomplished by several pathways including growth-factor and stress-mediated signaling. We have expanded the analysis of SGK1 regulation in epithelial cells. We used HA-tagged SGK1 to transiently transfect MDCK cells and study the regulation of SGK1 upon stimulation with HGF, cAMP or upon adhesion of the cells to immobilized fibronectin. In addition, we studied the regulation of SGK1 activity by small GTP-binding proteins of the Rho family.

Treatment of MDCK cells with HGF leads to a time-dependent activation of SGK1 that is blocked by wortmanin. This activation requires the conserved phosphorylation site present in the activation loop of the kinase (T256 in SGK1) and the phosphorylation site present in a hydrophobic domain at its C-terminus (S422 in SGK1), which are targets for PDK1/PDK2-mediated regulation of SGK1. We tested whether SGK1 could be activated by cAMP as it contains a putative PKA site. We were unable to demonstrate a significant activation of HA-SGK1 by cAMP stimulation under conditions where we detect cAMP-mediated phosphorylation of the transcription factor CREB.

Cotransfection of SGK1 with activated small GTP-binding proteins revealed that Rac1, but not Rho or Rap1, induces activation of SGK1. However, this activation was wortmanin insensitive and dominant-negative Rac1 did not inhibit the HGF-mediated activation of SGK1. Adhesion of MDCK cells to immobilized fibronectin also leads to activation of SGK1. However, it appears that the integrin-mediated activation of HA-SGK1 differs from AKT activation in the fact that AKT phosphorylation was blocked by wortmanin (or LY294002)whereas HA-SGK1 was not. The adhesion-dependent activation, however, requires the intact phosphorylation sites of SGK1. Co-transfection of HA-SGK1 with RacV12 results in increased activity in adherent cells compared with HA-SGK1 alone. Since RacN17 failed to inhibit adhesion dependent-activation of SGK1,it suggests that integrin activation is achieved by a parallel Rac-independent pathway.

The activation of SGK1 by HGF and integrin provides a link between HGF-mediated protection of MDCK from de-attachment induced apoptosis(anoikis). We demonstrate that dephosphorylation of the transcription factor FKRHL1 induced by cell de-attachment is prevented by activated SGK1,suggesting that SGK1 regulates cell survival pathways.

In summary, we demonstrate that SGK1 activation could be achieved through signaling pathways involved in the regulation of cell survival, cell-cell and cell-matrix interactions. SGK1 activation can be accomplished via HGF,PI-3K-dependent pathways and by integrin-mediated, PI-3K independent pathways. In addition, activation of SGK1 by the small GTP-binding protein Rac1 has been observed.
An ultrastructural study of the pancreatic acinar cell in mitosis, with special reference to changes in the golgi complex
Authors: Melmed R. N. , Benitez Carol J. , Holt J.
Published: April 2021

Changes occurring in the rat pancreatic acinar cell during mitosis have been studied by electron microscopy. Special attention has been given to those occurring in the Golgi complex. There is an initial increase in the number of small vesicles between the rough-surfaced endoplasmic reticulum and the saccules of the Golgi apparatus. These persist throughout the mitotic cycle. The Golgi apparatus becomes considerably smaller in metaphase. In anaphase the normal stacked appearance of its saccules is lost. In telophase the Golgi complex is restored to its normal interphase appearance and the small vesicles may contribute both to the reformation of its saccules and to the cleft forming between the daughter cells. Condensing vacuoles and zymogen granules appear to form throughout mitosis, although they have a much greater heterogeneity of size than in the interphase cell. The possible significance of some of these changes is discussed.
Chromosome analysis of two related heteroploid mouse cell lines by quinacrine fluorescence
Authors: Allderdice P. W. , Miller O. J. , Miller D. A. , Warburton D. , Pearson P. L. , Klein G. , Harris H.
Published: April 2021

The fluorescent banding patterns of quinacrine-stained metaphase chromosomes have been studied in 2 related mouse cell lines, A9 and a malignant derivative of A9, A9HT. In both cell lines virtually every chromosome has a distinctive banding pattern which permits its recognition. More than three quarters of the chromosomes have structural rearrangements, but the origin of nearly two thirds of the chromosomes could be determined by their banding patterns. The quinacrine fluorescence technique permits far more detailed characterization and comparison of heteroploid cell lines than any previous method. A9 and A9HT are karyologically quite similar, with many of the same marker chromosomes. There are, however, characteristic differences. A9HT, although it has a smaller average number of chromosomes per cell, appears to be more heterogeneous.
The spermatozoon of arthropoda: XVIII. the non-motile bifurcated sperm of psychodidae flies
Authors: Baccetti B. , Dallai R. , Burrini A. G.
Published: April 2021

The spermatozoa of some species of Diptera belonging to the Psychodidae are described. In the 4 species examined, they appear needle-shaped, non-motile, anteriorly flattened, posteriorly bifid. Flagella, and any microtubule system, are lacking, and the only organelles encountered are an extremely elongated nucleus, a prominent acrosome, a well developed subacrosomal body, a slender, somewhat elongated mitochondrial derivative and a conspicuous multilayered membrane wall, produced by the superimposition of the plasma membrane and the acrosomal membrane. The mitochondrion is devoid of a crystalline axis, while the acrosome contains a longitudinal, cross-striated para-crystalline body. Centrioles are absent throughout the spermatid stage. Sperms and spermatids are organized in syncytia of 210 elements.
The role of the epidermal cells in moulding the surface pattern of the cuticle in Rhodnius (hemiptera)
Authors: Wigglesworth V. B.
Published: April 2021

The patterns of folding in the epicuticle of Rhodnius result from mechanical forces directed by the epidermal cells and not from the action of physical forces arising spontaneously in the secreted substance. This conclusion is supported by observations on the cuticular folds over the abdomen of the larva and adult; on the formation of the plaques and the tactile setae arising from them; and on the taenidial folds in the tracheae.

At the time of formation of the outer epicuticle the boundaries of the definitive epidermal cells are clearly defined by adhesion zones. The total surface area of the cuticle is thus the sum of contributions determined by the individual cells.

The area of outer epicuticle deposited is greater than that of the apical plane of the cell. The cell surface is thrown into folds over which the epicuticle is laid down. But before the inner layers are deposited the cuticle is moulded by mechanical forces controlled by the epidermal cells.

Microtubules and fibre bundles appear to play an active part, notably in the outgrowth of setae, and perhaps in the raising of the initial folds in the abdominal surface and in the tracheae. The taenidial folds in the tracheae arise mainly at the sites of the folds in the preceding instar.

Cellular movements or changes in shape lead to aggregation of epidermal cells to form the ‘stellate pattern’ of the larval abdomen and the transverse ‘ripple pattern’ of the adult.

Distension of intercellular and intracellular vacuoles controls the moulding of the definitive stars in the larval cuticle, the transverse ridges in the adult, the smoothing of the cuticle over the plaques, the raising of the plaques in dome-like form above the rest of the cuticle, the expansion of the setae and the shaping of the taenidial folds in the tracheae.

The basement membrane provides a resistant substrate for these mechanical forces.
Human chromosomes in 18 man-mouse somatic hybrid cell lines analysed by quinacrine fluorescence
Authors: Allderdice P. W. , Miller O. J. , Pearson P. L. , Klein G. , Harris H.
Published: April 2021

Chromosome studies were done on 18 somatic hybrid cell lines produced by fusing cells of the mouse A 9 line with cells of the human Daudi lymphoblastoid line derived from a patient with Burkitt’s lymphoma. The human chromosomes were identified by their quinacrine fluorescent banding patterns. In one hybrid line the human chromosomes were identified also by the centromeric heterochromatin staining technique. Every human chromosome was identified in one or more of the hybrid lines. Some lines were homogeneous in terms of their human chromosome content, while others were quite heterogeneous. Detailed analysis of the A 9 chromosomes in one hybrid line showed very few changes in comparison with the chromosome constitution of the average A 9 cell.
Hherisomes, Hedgehog specialized recycling endosomes, are required for high level Hedgehog signaling and tissue growth
Authors: Pizette Sandrine , Matusek Tamás , Herpers Bram , Thérond Pascal P. , Rabouille Catherine
Published: April 2021

In metazoans, tissue growth and patterning is partly controlled by the Hedgehog (Hh) morphogen. Using immuno-electron microscopy on Drosophila wing imaginal discs, we identified a cellular structure, the Hherisomes, which contain the majority of intracellular Hh. Hherisomes are recycling tubular endosomes, and their formation is specifically boosted by overexpression of Hh. Expression of Rab11, a small GTPase involved in recycling endosomes, boosts the size of Hherisomes and their Hh concentration. Conversely, increased expression of the transporter Dispatched, a regulator of Hh secretion, leads to their clearance. We show that increasing Hh density in Hherisomes through Rab11 overexpression enhances both the level of Hh signaling and disc pouch growth, whereas Dispatched overexpression decreases high-level Hh signaling and growth. We propose that, upon secretion, a pool of Hh triggers low-level signaling, whereas a second pool of Hh is endocytosed and recycled through Hherisomes to stimulate high-level signaling and disc pouch growth. Altogether, our data indicate that Hherisomes are required to sustain physiological Hh activity necessary for patterning and tissue growth in the wing disc.
Sex in the Salicaceæ and its Modification by Eriophyid Mites and other Influences
Authors: Heslop Harrison J. W.
Published: April 2021

The species of the two genera Populus and Salix are ordinarily diœcious. In the whole of the British Salix species and hybrids examined a preponderance of female plants, slight in the diploid forms, but great in the polyploids, was discovered. In the diploids this excess, if significant, probably arises from the slower growth of pollen tubes carrying the male determining gametes. In the polyploids that influence is assisted (a) by the occurrence ofapomixis with thelytoky; (b) by pseudo-fertilisation with thelytoky; (c) by circumstances arising from peculiarities marking the chromosome complexes of polyploid diœcious plants. Hybrid Salices, when combinations of diploid species, invariably possess males. Other hybrids of which at least one parent is polyploid, are exclusively female as far as observation goes or, at best, produce but few males. These latter features may arise from circumstances detailed in (4), or there may be a deliberate and permanent switch-over of the heterogametic sex as in my Lycia-Nyssia crosses. Certain hybrids produce, in addition to plants of the normal male and female types, androgynous or monœcious forms. These are explained as arising through environmental influences temporarily switching the metabolism of a male plant over from its normal condition to that characteristic of the opposite sex. If that be the correct view the switch-over must occur, with a subsequent reversal, annually. In the Capreœ group intersexual florets occur. Such are induced by the attacks of parasites in the form of mites of the Eriophyid group, in particular of Epitriments salicobius. They act by effecting local changes in the metabolism of the plant. The phenomenon is thus one of parasitic castration. Many similar cases are known, for which, for the most part, fungi are responsible.
Genetical and Cytological Studies in Hybrid Roses
Authors: Blackburn Kathleen B. , Heslop Harrison J. W.
Published: April 2021

Rosa Sabini and R. Wilsoni are reciprocal crosses between R. pimpinellifolia and some Tomentosa microgene. Rosa pimpinellifolia is a balanced tetraploid, both the egg cell and the generative nucleus possessing 14 chromosomes. The Tomentosa microgenes are unbalanced pentaploids, the microspores, when functional, carrying 7 chromosomes in their nuclei, and the egg cells 28. Reciprocal crosses between R. pimpinellifolia and tomentosa forms should not therefore agree in chromosome complements. With pimpinellifolia as seed parent the cross should have 14 + 7 (= 21) in its somatic nuclei, and with the same plant as pollen parent the number should be 28 + 14 (= 42). R. Wilsoni undoubtedly has R. pimpinellifolia as seed parent, yet its chromosome number is 42. It has, therefore, like Primula Kewensis, doubled its original complement. In doing so, again like that hybrid, it has attained fertility.
The Function of the Anal Gills of the Mosquito Larva
Authors: Wigglesworth V. B.
Published: April 2021

In a recent paper (Wigglesworth, 1932a) the theory was put forward that the chief function of the so-called rectal glands of terrestrial insects is the reabsorption of water from the excreta in the rectum, and it was suggested that many of the supposedly respiratory structures in aquatic insects, such as the anal gills of the mosquito larva (which may perhaps be looked upon as homologous with rectal glands that have prolapsed through the anus), might also be concerned in absorbing water, not from the excreta, but from the surrounding medium. It has been shown in another place (Wigglesworth, 1932b) that the properties of the anal gills are such that they must almost certainly absorb water, but in the present paper this hypothesis will be proved experimentally.
Rheotaxis in Planaria Alpina
Authors: Beauchamp R. S. A.
Published: April 2021

Pl. alpina is normally active in the evening and quiescent during the day. Pl. alpina is shown to become positively rheotactic when developing sexually, but becomes negatively rheotactic on completing the sexual cycle. Starvation leads to de-dififerentiation and the loss of positive rheotaxy. Feeding produces a temporary positive rheotaxy and a temporary negative geotaxy. Continued feeding leads, if temperature conditions are suitable, to the re-development of those characters which produce positive rheotaxy in sexual individuals. The development and consequently the behaviour of PL alpina is controlled by temperature and the food supply. Considerable migrations up and down the stream are brought about by changes in the animal’s behaviour.
Double Hydropore in the Development of Asterias Glacialis
Authors: Narasimhamurti N.
Published: April 2021

A tendency to form a “primary madreporic” pore on the right side as well as on the left side exists in Atterias gladatif as in other star-fish and in Echinoderms generally. Metschnikoff as far back as 1874 figured and described a late larva of Asteracanthion with left and right hydropores and hydrocoeles (water-vascular rudiments). According to Field (1892) the double pore is frequently met with in the early larvae of Arterias vulgaris. MacBride (1896) has described a larva of Asterias with a pair of water-pores as well as others in the case of Echinus miliaris (1919). Gemmill (1914, 1916) observed double-pored larvae in Asterias rubens in the proportion of one to ten and in Asterias glaciatis in a slightly greater proportion.
Phosphagen in the Electrical Organ of Torpedo
Authors: Baldwin Ernest
Published: April 2021

The electrical organs of Torpedo marmorata contain creatine phosphoric acid, which was identified by the velocity constants of its hydrolysis under controlled conditions. This compound is of functional importance in the organ, being diminished in amount by activity, heat rigor, and by conditions which are unfavourable to the organism as a whole. The physiological parallel between the electrical organ and muscle appears, as far as this study has been carried, to be itself paralleled by the chemical mechanisms. Creatine has been isolated from the electrical organ and has been identified, in confirmation of the earlier work of other authors.
The Electrocardiogram of the Developing Chick
Authors: Bogue J. Yule
Published: April 2021

In the investigation of the electrocardiogram of the chick embryo the same technique has been employed as that already described by the author (1932). The only point of difference is that in the present experiments after a record had been taken through the shell, the shell was opened, the embryo exposed and the electrodes placed in the most favourable position for obtaining a record.
Central Nervous Integration of Cardiovascular Control
Authors: Spyer K. M.
Published: April 2021

In this account an attempt has been made to identify integrative interactions in the control of the cardiovascular system. Three main sites of such interaction have been considered, the nucleus of the tractus solitarius (NTS), the vagal preganglionic supply to the heart and sympathetic preganglionic neurones.

In the case of the NTS the extent and range of afferent inputs from cardiovascular and respiratory receptors have been reviewed. In addition the interactions of these inputs on the activity of NTS neurones have been indicated although the details are as yet vague. With respect to the baroreceptor reflex, it is clear that its relay through the NTS permits the action of intrinsic drives, such as inspiratory activity, and extrinsic drives, for example the defence reaction, to modify to a greater, or lesser, extent the efficacy of the reflex. In the case of respiratory activity, changes in transmission of baroreceptor activity through the NTS are minimal, since a baroreceptor effect can be shown to exert itself on CVM activity throughout the respiratory cycle under appropriate experimental conditions (McAllen & Spyer, 1978b). The effectiveness of this excitatory input is, however, ‘gated’ by a direct inspiratory control of CVM activity. This indicates an essentially integrative role of vagal preganglionic neurones. The role of inputs from the lungs themselves evoked during inspiration, which also contribute to the respiratory modifications of the baroreceptor reflex, in the control of CVM activity is as yet uncertain although evidence is accumulating to suggest that they act by a mechanism different from that of inspiratory drive.

The influence of the defence reaction on transmission through the NTS has yet to be fully documented, but it appears as if there may be the potential for a marked modification. However, it is now certain that an inhibitory control of CVM activity can be evoked from the hypothalamus which is independent of any modification of the baroreceptor input at that level of the NTS and acts rather through an inhibitory synaptic influence directly onto CVMs.

In much the same way the baroreceptor influence on sympathetic preganglionic neurones is determined by their excitability, an excitability which is dependent on the balance of activity in several bulbospinal inhibitory and excitatory pathways, as well as segmental inputs. The role, if any, of direct hypothalamo-spinal pathways and the nature and organization of the descending pathways involved in the defence reaction requires elucidation. Existing data, however, make it clear that the thoracic intermedio-lateral cell column is an important site in the integration of cardiovascular control.
Respiratory and Circulatory Control at High Altitudes
Authors: West John B.
Published: April 2021

Hyperventilation is one of the most important features of acclimatization to high altitude. Resting ventilation at extreme altitudes increases up to fourfold and exercise ventilation for a given work level increases to the same extent. Hypoxic stimulation of the peripheral chemoreceptors is the chief mechanism for the hyperventilation but there is also evidence that central sensitization of the respiratory centres occurs. Permanent residents of high altitude have a blunted hypoxic ventilatory response compared to acclimatized lowlanders. Cardiac output increases in response to acute hypoxia but returns to normal in acclimatized lowlanders. Oxygen uptake at extreme altitudes is markedly limited by the diffusion properties of the blood gas barrier. As a consequence the maximal oxygen consumption of a climber near the summit of Mount Everest is near his basal oxygen requirements. Maximal oxygen consumption is so sensitive to barometric pressure that it may be that day-to-day variations will affect the chances of a climber reaching the summit without supplementary oxygen.
Cardiopulmonary Coupling During Exercise
Authors: Whipp Brian J. , Ward Susan A.
Published: April 2021

Muscular exercise imposes the most potent sustained stress to cellular energetics. At work rates below the anaerobic threshold (i.e. no sustained lactic acidosis), the ventilatory and cardiovascular responses regulate arterial , [H+] and at or close to their resting levels in the steady state. However, dynamic forcing and systems-analytic techniques reveal two phases of the non-steady-state response dynamics. In the first phase, increased gas flow to the lungs results solely from increased pulmonary blood flow , with alveolar gas tensions being maintained at their resting levels by a coupled increase in ventilation : evidence for cardiopulmonary coupling being provided by experimentally-altered in man and dog. Arterial chemoreception does not impose humoral feedback control in this phase. Rather, rapid feedforward mechanisms operate, with both intrathoracic (largely cardiac) and exercising-limb mechanoreception proposed as afferent sources. In the second phase, cardiogenic gas flow to the lungs is augmented by altered mixed venous blood gas contents ; ventilation responding exponentially with a time constant (τ) which is an inverse function of carotid body gain. The close dynamic coupling of with CO2 output in this phase results in arterial and [H+] being maintained close to their resting levels. However, the kinetic dissociation between and O2 uptake, with , leads to an appreciable transient fall of arterial . The respiratory compensation for the sustained lactic acidosis at higher work rates is predominantly mediated by the carotid bodies in man: the aortic bodies subserving no discernible role. Control of the respiratory and circulatory responses to exercise is therefore mediated by both neural and humoral mechanisms : and an important control link appears to couple the responses, via feedforward ventilatory control of cardiac origin.
Role of Peripheral Chemoreceptors and Central Chemosensitivity in the Regulation of Respiration And Circulation
Authors: O’regan R. G. , Majcherczyk S.
Published: April 2021

Adjustments of respiration and circulation in response to alterations in the levels of oxygen, carbon dioxide and hydrogen ions in the body fluids are mediated by two distinct chemoreceptive elements, situated peripherally and centrally. The peripheral arterial chemoreceptors, located in the carotid and aortic bodies, are supplied with sensory fibres coursing in the sinus and aortic nerves, and also receive sympathetic and parasympathetic motor innervations. The carotid receptors, and some aortic receptors, are essential for the immediate ventilatory and arterial pressure increases during acute hypoxic hypoxaemia, and also make an important contribution to respiratory compensation for acute disturbances of acid-base balance. The vascular effects of peripheral chemoreceptor stimulation include coronary vasodilation and vasoconstriction in skeletal muscle and the splanchnic area. The bradycardia and peripheral vasoconstriction during carotid chemoreceptor stimulation can be lessened or reversed by effects arising from a concurrent hyperpnoea.

Central chemoreceptive elements respond to changes in the hydrogen ion concentration in the interstitial fluid in the brain, and are chiefly responsible for ventilatory and circulatory adjustments during hypercapnia and chronic disturbances of acid-base balance. The proposal that the neurones responsible for central chemoreception are located superficially in the ventrolateral portion of the medulla oblongata is not universally accepted, mainly because of a lack of convincing morphological and electrophysiological evidence. Central chemosensitive structures can modify peripheral chemoreceptor responses by altering discharges in parasympathetic and sympathetic nerves supplying these receptors, and such modifications could be a factor contributing to ventilatory unresponsiveness in mild hypoxia. Conversely, peripheral chemoreceptor drive can modulate central chemosensitivity during hypercapnia.