On transfer times in tracer experiments

A compartment is defined as a pool of material whose behavior can be described by a deterministic or by a stochastic equation; these two equations are used to define the transit time through the compartment, the total residence time, the time of entrance and the time of exit.If in a complex system one or more compartments are accessible, the transport of material through it can be studied using a tracer. Then the transfer time between any two compartments, or through the cycle around a compartment, can be analyzed under certain hypotheses, even if the transport along the route considered cannot be described by compartment equations.     

Chemotaxonomic notes on Porphyridium Näg. (Rhodophyta,Porphyridiales)

Abstract

The taxonomic attribution of Porphyridium Näg. to Rhodophyta is a question from a long time debated since Porphyridium lacks both the morphological and the reproductive features of the red algae.

In the present paper we report the presence of floridosides and γ-linolenic acid in P. aerugineum and P. cruentum. Both these compounds are believed to be useful in the elucidation of the rhodophycean phylogeny; thus we support the attribution of Porphyridium to Rhodophyta.

Phylogenetic relationships between Porphyridium and other red algae are discussed.     

The MIS12 complex is a protein interaction hub for outer kinetochore assembly

Kinetochores are nucleoprotein assemblies responsible for the attachment of chromosomes to spindle microtubules during mitosis. The KMN network, a crucial constituent of the outer kinetochore, creates an interface that connects microtubules to centromeric chromatin. The NDC80, MIS12, and KNL1 complexes form the core of the KMN network. We recently reported the structural organization of the human NDC80 complex. In this study, we extend our analysis to the human MIS12 complex and show that it has an elongated structure with a long axis of ∼22 nm. Through biochemical analysis, cross-linking–based methods, and negative-stain electron microscopy, we investigated the reciprocal organization of the subunits of the MIS12 complex and their contacts with the rest of the KMN network. A highlight of our findings is the identification of the NSL1 subunit as a scaffold supporting interactions of the MIS12 complex with the NDC80 and KNL1 complexes. Our analysis has important implications for understanding kinetochore organization in different organisms.     

Genetic differentiation,speciation, and phylogeography of cactus flies (Diptera: Neriidae: Odontoloxozus) from Mexico and south‐western USA

Nucleotide sequences from the mitochondrial cytochrome c oxidase subunit I (COI) gene, comprising the standard barcode segment, were used to examine genetic differentiation, systematics, and population structure of cactus flies (Diptera: Neriidae: Odontoloxozus) from Mexico and south‐western USA. Phylogenetic analyses revealed that samples of Odontoloxozus partitioned into two distinct clusters: one comprising the widely distributed Odontoloxozus longicornis (Coquillett) and the other comprising Odontoloxozus pachycericola Mangan & Baldwin, a recently described species from the Cape Region of the Baja California peninsula, which we show is distributed northward to southern California, USA. A mean Kimura two‐parameter genetic distance of 2.8% between O. longicornis and O. pachycericola, and eight diagnostic nucleotide substitutions in the COI gene segment, are consistent with a species‐level separation, thus providing the first independent molecular support for recognizing O. pachycericola as a distinct species. We also show that the only external morphological character considered to separate adults of the two species (number of anepisternal bristles) varies with body size and is therefore uninformative for making species assignments. Analysis of molecular variance indicated significant structure among populations of O. longicornis from three main geographical areas, (1) Arizona, USA and Sonora, Mexico; (2) Santa Catalina Island, California, USA; and (3) central Mexico (Querétaro and Guanajuato), although widely‐separated populations from Arizona and Sonora showed no evidence of structure. A TCS haplotype network showed no shared haplotypes of O. longicornis among the three main regions. The potential roles of vicariance and isolation‐by‐distance in restricting gene flow and promoting genetic differentiation and speciation in Odontoloxozus are discussed. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 245–256.     

Myosin-Va-Dependent Cell-To-Cell Transfer of RNA from Schwann Cells to Axons

To better understand the role of protein synthesis in axons, we have identified the source of a portion of axonal RNA. We show that proximal segments of transected sciatic nerves accumulate newly-synthesized RNA in axons. This RNA is synthesized in Schwann cells because the RNA was labeled in the complete absence of neuronal cell bodies both in vitro and in vivo. We also demonstrate that the transfer is prevented by disruption of actin and that it fails to occur in the absence of myosin-Va. Our results demonstrate cell-to-cell transfer of RNA and identify part of the mechanism required for transfer. The induction of cell-to-cell RNA transfer by injury suggests that interventions following injury or degeneration, particularly gene therapy, may be accomplished by applying them to nearby glial cells (or implanted stem cells) at the site of injury to promote regeneration.     

Ultrastructural features of cytofilaments within mammalian endothelial cells

Summary A submicroscopic study of the endothelium lining the blood capillaries and arterioles contained in the Cyon's nerve was made. The cytoplasm of some endothelial cells was found containing bundles of thin filaments. These measure about 60 Å in diameter, and do not show any cross striation, nor contacts with other cytoplasmic components. They are oriented parallel to each other and to the cell surface. No attachment plate of cytofilaments to the plasma membrane was seen. The filamentous structures were mostly found within the supranuclear cytoplasm. The endothelial cells in question never showed contacts with axons.In the light of these findings it can be advanced the view that the cytofilaments present in endothelial cells are supportive in function; namely they may confer a higher elasticity to these cells, subject to continuous pressure and morphological variations.

---

Riassunto Lo studio ultrastrutturale dell'endotelio di piccoli vasi sanguigni contenuti nel nervo cardio-aortico depressore di Cyon del coniglio ha consentito di rilevare la presenza in alcune cellule endoteliali di esili filamenti raggruppati in fasci più o meno numerosi. Detti citofilamenti presentano uno spessore di circa 60 Å, occupano per lo più il citoplasma sopranucleare e sono orientati parallelamente tra loro e rispetto alla superficie cellulare. Essi non mostrano struttura periodica né rapporto alcuno, se non di semplice contiguità, con altre componenti citoplasmatiche. Non presentano, inoltre, punti di attacco sulla membrana cellulare, né connessioni con fibre nervose. Numerose le vescicole pinocitotiche osservate lungo i bordi superficiale e basale delle cellule endoteliali in oggetto.In base a tali reperti si avanza l'ipotesi che i citofilamenti endoteliali svolgano una funzione di sostegno nell'ambito del citoplasma, e siano capaci di conferire un più elevato grado di elasticità all'endotelio vasale, soggetto a continue variazioni di pressione e di forma.

---

---

Dedicated to Prof. Wolfgang Bargmann on his 60th birthday.—This investigation was supported in part by a grant from the Italian C.N.R.

---

The author wishes to thank Dr. Pasquale Romeo for his kind help in the preparation of the paper, and Mr. Ciro Paesano for making the photographic prints.     

Segnalazione di piante nuove,inedite, o notevoli per la regione marchigiana. III

Abstract

A report about new or interesting plants in the Marche region. III. — The authors report about the occurrence in the Marche of 61 entities of specific or infraspecific rank, 22 of which are new or unpublished concerning the region, while the remaining 39 have been previously very little or imprecisely mentioned; as to the latter new localities and stations are shown or general information on the distribution over the Marche district has been supplied. Out of the first 22 entities, 18 (Fumaria muralis subsp. muralis, Cardamine flexuosa, Lunaria annua subsp. pachyrhiza, Colutea arborescens subsp. gallica, Astragalus monspessulanas subsp. illyricus, Cornus sanguinea subsp. australis, Galium verrucosum, Hedypnois rhagadioloides subsp. tubaeformis, Andryala tenuifolia, Sonchus asper subsp. glaucescens, Rheichardia picroides var. maritima, Podospermum canum, Scorzonera austriaca, S. hirsuta, Bidens frondosa, Guizotia abyssinica, Ambrosia elatior, A. trifida) are, as far as the authors know, quite new or unpublished concerning the Marche, while 4 (Rumex angiocarpus, Trifolium repens subsp. prostratum, Epilobium lanceolatum, Picris hieracioides subsp. spinulosa) are generally reported in Middle Italy or over the whole Italian territory by the general Floras, but till now have not been mentioned in works dealing with regional flora.