Comparative ultrastructure of plasmodesmata of Chara and selected bryophytes: towards an elucidation of the evolutionary origin of plant plasmodesmata

We have used transmission electron microscopy to examine plasmodesmata of the charophycean green alga Chara zeylanica, and of the putatively early divergent bryophytes Monoclea gottschei (liverwort), Notothylas orbicularis (hornwort), and Sphagnum fimbriatum (moss), in an attempt to learn when seed plant plasmodesmata may have originated. The three bryophytes examined have desmotubules. In addition, Monoclea was found to have branched plasmodesmata, and plasmodesmata of Sphagnum displayed densely staining regions around the neck region, as well as ring-like wall specializations. In Chara, longitudinal sections revealed endoplasmic reticulum (ER) that sometimes appeared to be associated with plasmodesmata, but this was rare, despite abundant ER at the cell periphery. Across all three fixation methods, cross-sectional views showed an internal central structure, which in some cases appeared to be connected to the plasma membrane via spoke-like structures. Plasmodesmata were present even in the incompletely formed reticulum of forming cell plates, from which we conclude that primary plasmodesmata are formed at cytokinesis in Chara zeylanica. Based on these results it appears that plasmodesmata of Chara may be less specialized than those of seed plants, and that complex plasmodesmata probably evolved in the ancestor of land plants before extant lineages of bryophytes diverged

Hematopoietic Stem Cells Are the Major Source of Multilineage Hematopoiesis in Adult Animals

Hematopoietic stem cells (HSCs) sustain long-term reconstitution of hematopoiesis in transplantation recipients, yet their role in the endogenous steady-state hematopoiesis remains unclear. In particular, recent studies suggested that HSCs provide a relatively minor contribution to immune cell development in adults. We directed transgene expression in a fraction of HSCs that maintained reconstituting activity during serial transplantations. Inducible genetic labeling showed that transgene-expressing HSCs gave rise to other phenotypic HSCs, confirming their top position in the differentiation hierarchy. The labeled HSCs rapidly contributed to committed progenitors of all lineages and to mature myeloid cells and lymphocytes, but not to B-1a cells or tissue macrophages. Importantly, labeled HSCs gave rise to more than two-thirds of all myeloid cells and platelets in adult mice, and this contribution could be accelerated by an induced interferon response. Thus, classically defined HSCs maintain immune cell development in the steady state and during systemic cytokine responses

Extracellular matrix assembly in diatoms (Bacillariophyceae). IV. Ultrastructure of Achnanthes longipes and Cymbella cistula as revealed by high-pressure freezing/freeze substituton and cryo-field emission scanning electron microscopy

Extracellular matrix (ECM) polymers secreted by the diatoms Achnanthes longipes Ag. and Cymbella cistula (Ehr.) Kirchn. completely encase the cell and are responsible for adhesion and other interactions with the external environment. To preserve details of the highly hydrophilic ECM in the native state and to preserve, with a high degree of fidelity, the intracellular structures involved in synthesis of extracellular polymers, we applied a suite of cryotechniques. The methods included high-resolution visualization of surfaces using cryo-field emission SEM (cryo-FESEM) and preservation for TEM observation of thin sections by high-pressure freezing (HPF) and freeze substitution (FS). The extracellular structures of diatoms plunge-frozen in liquid ethane, etched at low temperature, and observed on a cryostage in the FESEM showed overall dimensions and shapes closely comparable to those observed with light microscopy. Cryo-FESEM demonstrated the pervasive nature of the extracellular polymers and their importance in cell-substratum and cell-cell associations and revealed details of cell attachment processes not visible using other SEM techniques or light microscopy. The layer of ECM coating the frustule and entirely encapsulating cells of A. longipes and C. cistula was shown to have a significant role in initial cell adhesion and subsequent interaction with the environment. Trails of raphe-associated ECM, generated during cell motility, were shown at high resolution and consist of anastomoses of coiled and linear strands. Cryo-FESEM revealed a sheet-like mucilage covering stalks. HPF/FS of A. longipes resulted in excellent preservation of intra- and extracellular structures comparable to previous reports for animals and higher plants and revealed several organelles not described previously. Three distinct vesicle types were identified, including a class closely associated with Golgi bodies and postulated to participate in formation of the extracellular adhesive structures. HPF/FS showed a number of continuous diatotepic layers positioned between the plasma membrane and the silicon frustule and revealed that extracellular adhesive extrusion through frustule pores during stalk production was closely related to the diatotepum. The stalks of A. longipes consist of highly organized, multilayered, fine fibrillar materials with an electron-opaque layer organized as a sheath at the stalk periphery

Edgar Paiewonsky-Conde, Lila Zemborain, Tonia León, Ana Maria Fuster Lavin, Maria Negroni, Michael Burkard, Jules Gibbs, Jaime Garcia Maffla, Gloria Posada, Josefina Baez, Colleen Kattau, Tamara Kamenszain folio

A folio of Spanish- and English-language verse and prose poetry by Edgar Paiewonsky-Conde, Lila Zemborain, Tonia León, Ana Maria Fuster Lavin, Maria Negroni, Michael Burkard, Jules Gibbs, Jaime Garcia Maffla, Gloria Posada, Josefina Baez, Colleen Kattau and Tamara Kamenszain

Hematopoietic Stem Cells Are the Major Source of Multilineage Hematopoiesis in Adult Animals

Hematopoietic stem cells (HSCs) sustain long-term reconstitution of hematopoiesis in transplantation recipients, yet their role in the endogenous steady-state hematopoiesis remains unclear. In particular, recent studies suggested that HSCs provide a relatively minor contribution to immune cell development in adults. We directed transgene expression in a fraction of HSCs that maintained reconstituting activity during serial transplantations. Inducible genetic labeling showed that transgene-expressing HSCs gave rise to other phenotypic HSCs, confirming their top position in the differentiation hierarchy. The labeled HSCs rapidly contributed to committed progenitors of all lineages and to mature myeloid cells and lymphocytes, but not to B-1a cells or tissue macrophages. Importantly, labeled HSCs gave rise to more than two-thirds of all myeloid cells and platelets in adult mice, and this contribution could be accelerated by an induced interferon response. Thus, classically defined HSCs maintain immune cell development in the steady state and during systemic cytokine responses

Droit naturel : relancer l'histoire

The extracellular matrix comprises a network of macromolecules such as collagens, proteoglycans and glycoproteins. VWA1 (von Willebrand factor A domain containing 1) encodes a component of the extracellular matrix that interacts with perlecan/collagen VI, appears to be involved in stabilizing extracellular matrix structures, and demonstrates high expression levels in tibial nerve. Vwa1-deficient mice manifest with abnormal peripheral nerve structure/function; however, VWA1 variants have not previously been associated with human disease. By interrogating the genome sequences of 74 180 individuals from the 100K Genomes Project in combination with international gene-matching efforts and targeted sequencing, we identified 17 individuals from 15 families with an autosomal-recessive, non-length dependent, hereditary motor neuropathy and rare biallelic variants in VWA1. A single disease-associated allele p.(G25Rfs*74), a 10-bp repeat expansion, was observed in 14/15 families and was homozygous in 10/15. Given an allele frequency in European populations approaching 1/1000, the seven unrelated homozygote individuals ascertained from the 100K Genomes Project represents a substantial enrichment above expected. Haplotype analysis identified a shared 220 kb region suggesting that this founder mutation arose 47000 years ago. A wide age-range of patients (6-83 years) helped delineate the clinical phenotype over time. The commonest disease presentation in the cohort was an early-onset (mean 2.0 +/- 1.4 years) non-length-dependent axonal hereditary motor neuropathy, confirmed on electrophysiology, which will have to be differentiated from other predominantly or pure motor neuropathies and neuronopathies. Because of slow disease progression, ambulation was largely preserved. Neurophysiology, muscle histopathology, and muscle MRI findings typically revealed clear neurogenic changes with single isolated cases displaying additional myopathic process. We speculate that a few findings of myopathic changes might be secondary to chronic denervation rather than indicating an additional myopathic disease process. Duplex reverse transcription polymerase chain reaction and immunoblotting using patient fibroblasts revealed that the founder allele results in partial nonsense mediated decay and an absence of detectable protein. CRISPR and morpholino vwa1 modelling in zebrafish demonstrated reductions in motor neuron axonal growth, synaptic formation in the skeletal muscles and locomotive behaviour. In summary, we estimate that biallelic variants in VWA1 may be responsible for up to 1% of unexplained hereditary motor neuropathy cases in Europeans. The detailed clinical characterization provided here will facilitate targeted testing on suitable patient cohorts. This novel disease gene may have previously evaded detection because of high GC content, consequential low coverage and computational difficulties associated with robustly detecting repeat-expansions. Reviewing previously unsolved exomes using lower QC filters may generate further diagnoses