Do neurons in the vertebrate CNS migrate on laminin?

In adult rat brain the extracellular matrix glycoprotein, laminin, is found only in basement membranes, but is transiently expressed by astrocytes after brain injury. Here, I show that laminin also appears in immature brain cells during CNS development, and that its presence coincides with phases of neuronal migration. In early embryos, laminin is seen throughout the whole thickness of the forming brain, and is apparently synthesized by the cells, as judged by its intracytoplasmic localization. As development proceeds, intracellular laminin becomes restricted to the periventricular regions while punctate deposits of laminin follow the course of vimentin-positive radial glial fibers. In most brain regions, the adult pattern of laminin expression is achieved by birth. In the post-natal rat cerebellum, however, laminin is detected in external granule cells, in Purkinje cells, and in punctate deposits along the radial Bergmann glial fibers. By day 24 after birth, when the migration of external granule cells is complete, all laminin immunoreactivity disappears from these structures. The transient expression of laminin in regions where neurons are migrating raises the possibility that laminin plays a role in neuronal migration during CNS development.     

What are the roles of retinoids,other morphogens,and Hox genes in setting up the vertebrate body axis?

This article is concerned with the roles of retinoids and other known anterior–posterior morphogens in setting up the embryonic vertebrate anterior–posterior axis. The discussion is restricted to the very earliest events in setting up the anterior–posterior axis (from blastula to tailbud stages in Xenopus embryos). In these earliest developmental stages, morphogen concentration gradients are not relevant for setting up this axis. It emerges that at these stages, the core patterning mechanism is timing: BMP‐anti BMP mediated time space translation that regulates Hox temporal and spatial collinearities and Hox‐Hox auto‐ and cross‐ regulation. The known anterior–posterior morphogens and signaling pathways––retinoids, FGF's, Cdx, Wnts, Gdf11 and others––interact with this core mechanism at and after space–time defined “decision points,” leading to the separation of distinct axial domains. There are also other roles for signaling pathways. Besides the Hox regulated hindbrain/trunk part of the axis, there is a rostral part (including the anterior part of the head and the extreme anterior domain [EAD]) that appears to be regulated by additional mechanisms. Key aspects of anterior–posterior axial patterning, including: the nature of different phases in early patterning and in the whole process; the specificities of Hox action and of intercellular signaling; and the mechanisms of Hox temporal and spatial collinearities, are discussed in relation to the facts and hypotheses proposed above.     

Did the first insects live in water or in air?

We evaluate the arguments and evidence for a terrestrial vs an aquatic origin for the Insecta. The evidence falls into three categories: (1) evidence that does not support one view more than the other; (2) speculative evidence, which should carry little weight; and (3) evidence that does support one view more than the other. Category 1 includes evidence from locomotory and osmoregulatory systems; plausible functions have been proposed for 'protowings' in both aquatic and terrestrial environments, while locomotory and osmoregulatory mechanisms of insects shed little light on their origins. Fossils, phylogenetic speculation, gill structure and life histories fall into category 2, in which, although speculative, the evidence favours a terrestrial origin. The earliest fossil hexapods were apparently terrestrial and unequivocally aquatic hexapods do not appear until 60–70 million years later, while sister-group relationships point to a terrestrial life style from at least the Hexapoda-Myriapoda stem group. The great variation in gill structure, even within orders, suggests convergence, and the more or less completely aquatic life histories are better interpreted as steps towards independence from land, rather than signs of an aquatic origin. Category 3 includes evidence from the tracheal system. In order to have evolved in water, a tracheal system must have first invaginated, then connected with the body wall for gas exchange with the water, and thirdly connected with the internal organs. It is difficult to envisage functions for the first two stages; on the other hand, the system could have readily evolved on land by invagination of respiratory surfaces, and then have been modified to effect gas exchange in water via gills.     

Trapped in the extinction vortex? Strong genetic effects in a declining vertebrate population

Background  

Inbreeding and loss of genetic diversity are expected to increase the extinction risk of small populations, but detailed tests in natural populations are scarce. We combine long-term population and fitness data with those from two types of molecular markers to examine the role of genetic effects in a declining metapopulation of southern dunlins Calidris alpina schinzii, an endangered shorebird.     

Flexibility in the order of action and in the enzymology of the nuclease, polymerases, and ligase of vertebrate non-homologous DNA end joining： relevance to cancer, aging, and the immune system

Nonhomologous DNA end joining （NHEJ） is the primary pathway for repair of double-strand DNA breaks in human cells and in multicellular eukaryotes. The causes of double-strand breaks often fragment the DNA at the site of damage, resulting in the loss of information there. NHEJ does not restore the lost information and may resect additional nucleotides during the repair process. The ability to repair a wide range of overhang and damage configurations reflects the flexibility of the nuclease, polymerases, and ligase of NHEJ. The flexibility of the individual components also explains the large number of ways in which NHEJ can repair any given pair of DNA ends. The loss of information locally at sites of NHEJ repair may contribute to cancer and aging, but the action by NHEJ ensures that entire segments of chromosomes are not lost.     

The fossil vertebrate locality Kossom Bougoudi,Djurab desert,Chad: A window in the distribution of the carnivoran faunas at the Mio–Pliocene boundary in Africa

The fossil vertebrate bearing locality Kossom Bougoudi (KB) is situated in the Djurab desert (Chad, Africa), 600 km north-east of N’djamena. It has yielded about 1250 specimens with many mammalian remains, principally artiodactyls. Its geologic age has been estimated to be about 5 Ma by biochronologic estimation and about 5.3 Ma by radiometric studies on cosmogenic nuclides of beryllium (authigenic ¹⁰B/⁹B). The carnivoran fauna contains few specimens which belong to five different families. All the taxa were unknown in central Africa. A large lutrine is close to Sivaonyx but different from known species of the genus. Another large lutrine is similar by its size to a species described from the Middle Pliocene of Uganda. An edentulous mandible of a small machairodont cat resembles a small species of Dinofelis, while a distal humerus indicates the presence of a larger member of the same genus. A hunting hyaenid is also much like the European species. An unidentified canid reaches the size of the recent Canis aureus and an isolated calcaneum matches that of the large extant viverrid. This small fauna allows a first look at the guild of the carnivorans at the Latest Miocene–Pliocene boundary in Central Africa and is a milestone between North African, East African and South African carnivore faunas.     

Variability in secondary structure of the antimicrobial peptide Cateslytin in powder,solution, DPC micelles and at the air–water interface

Cateslytin (bCGA ³⁴⁴RSMRLSFRARGYGFR³⁵⁸), a five positively charged 15 amino-acid residues arginine-rich antimicrobial peptide, was synthesized using a very efficient procedure leading to high yields and to a 99% purity as determined by HPLC and mass spectrometry. Circular dichroism, polarized attenuated total reflectance fourier transformed infrared, polarization modulation infrared reflection Absorption spectroscopies and proton two-dimensional NMR revealed the flexibility of such a peptide. Whereas being mostly disordered as a dry powder or in water solution, the peptide acquires a α-helical character in the “membrane mimicking” solvent trifuoroethanol. In zwitterionic micelles of dodecylphophatidylcholine the helical character is retained but to a lesser extent, the peptide returning mainly to its disordered state. A β-sheet contribution of almost 100% is detected at the air–water interface. Such conformational plasticity is discussed regarding the antimicrobial action of Cateslytin. Presented at the joint biannual meeting of the SFB-GEIMM-GRIP, Anglet France, 14–19 October, 2006.     

Something in the air? New insights into mammalian pheromones

Olfaction is the dominant sensory modality for most animals and chemosensory communication is particularly well developed in many mammals. Our understanding of this form of communication has grown rapidly over the last ten years since the identification of the first olfactory receptor genes. The subsequent cloning of genes for rodent vomeronasal receptors, which are important in pheromone detection, has revealed an unexpected diversity of around 250 receptors belonging to two structurally different classes. This review will focus on the chemical nature of mammalian pheromones and the complementary roles of the main olfactory system and vomeronasal system in mediating pheromonal responses. Recent studies using genetically modified mice and electrophysiological recordings have highlighted the complexities of chemosensory communication via the vomeronasal system and the role of this system in handling information about sex and genetic identity. Although the vomeronasal organ is often regarded as only a pheromone detector, evidence is emerging that suggests it might respond to a much broader variety of chemosignals.     

Hierarchies of evolutionary radiation in the world’s most species rich vertebrate group,the Neotropical Pristimantis leaf litter frogs

The Neotropical leaf litter frog genus Pristimantis is very species-rich, with 526 species described to date, but the full extent of its diversity is much higher and remains unknown. This study explores the phylogenetic processes and resulting evolutionary patterns of diversification in Pristimantis. Given the well-recognised failure of morphology- and community-based species groups to describe diversity within the genus, we apply a new test for the presence and phylogenetic distribution of higher evolutionary units. We developed a phylogeny based on 260 individuals encompassing 149 Pristimantis presumed species, sampled at mitochondrial and nuclear genes (3718 base pair alignment), combining new and available sequence data. Our phylogeny broadly agrees with previous studies, both in topology and age estimates, with the origin of Pristimantis at 28.97 (95% HDP =21.59 – 37.33) million years ago (MYA). New taxa that we add to the genus, which had not previously been included in Pristimantis phylogenies, suggest considerable diversity remains to be described. We assessed patterns of lineage origin and recovered 14 most likely (95% CI: 13–19) phylogenetic clusters or higher evolutionary significant units (hESUs) within Pristimantis. Diversification rates decrease towards the present following a density-dependent pattern for Pristimantis overall and for most hESU clusters, reflecting historical evolutionary radiation. The timing of diversification suggests that geological events in the Miocene, such as Andes orogenesis and Pebas system formation and drainage, may have had a direct or indirect impact on the evolution of Pristimantis and thus contributed to the origins of evolutionary independent phylogenetic clusters.     

Regulation of potassium levels by Müller cells in the vertebrate retina

The membrane properties of Müller cells, the principal glial cells of the vertebrate retina, have been characterized in a series of physiological experiments on freshly dissociated cells. In species lacking a retinal circulation (tiger salamander, rabbit, guinea pig), the end-foot of the Müller cell has a much higher K+ conductance than do other cell regions. In species with retinal circulation (mouse, cat, owl monkey) the K+ conductance of the end-foot is greater than the conductance of the proximal process of the cell. In these species, however, the K+ conductance of the soma and distal process is equal to, or greater than, the end-foot conductance. Müller cells also possess four voltage-dependent ion channels, including an inward rectifying K+ channel. These membrane specializations may aid in the regulation of extracellular K+ levels by Müller cells in the retina. High end-foot conductance shunts excess K+ out through the end-foot, where it diffuses into the vitreous humor. In vascularized retinae, excess K+ may also be transferred to the ablumenal wall of capillaries, where it could be transported into the blood.     

Egg timers: how is developmental time measured in the early vertebrate embryo?

Eggs and early embryos appear to be programmed to undertake particular developmental decisions at characteristic times, although precisely how these decisions are timed is unknown. We discuss the possible roles and interactions during early vertebrate development of two broad categories of timers: 1) those that involve cyclic or sequential mechanisms, referred to as clocks; and 2) those that require an increase or decrease in some factor to a threshold level for progression of time, referred to as hourglass timers. It is concluded that both clock-like timers linked to various features of the cell cycle and hourglass timers are involved in early developmental timing. The possible involvement of elements of circadian clock timers is also considered. BioEssays 22:57-63, 2000.     

Airborne pollen concentrations,solid particle content in the air and allergy symptoms in Córdoba (Spain)

During 1991 and 1992, hourly measurements were taken of solid particulates (size, 22–25 μm).Olea and grass pollen and spores. The results were then compared with symptoms recorded in patients consulting the Allergy Unit during the period of highest pollen concentrations (April–June). The spore-trap slides were studied by spectrophotometry in order to analyse the total solid particulates content in the air as a possible synergic agent of the pollen. This allowed the volume of material present in the air to be determined and expressed as a percentage of total optical density (OD). Allergy symptom data were obtained from the study of subjective clinical records completed by patients, who were required to note down the severity of a selected series of symptoms every 4 h using a scale from 0–3. The results showed a clear link during the season between hourly peaks and pollen concentrations, and the different patterns of response associated with the dominant pollen types. An attempt has been made to determine whether a relationship exists between the increment of the optical density and the symptomatic response. The positive relationship encountered seems to indicate that a synergic agent takes an active part in the effects produced by pollen in the patients.     

Has vertebrate chemesthesis been a selective agent in the evolution of arthropod chemical defenses?

Arthropods use a variety of chemical substances to repel potential predators, but how did they arrive at the suite of chemicals that they use? One way to explore this question is to map chemically defended arthropod species in a multidimensional "compound" space. Clustering within this space indicates species that share similar combinations of chemical compounds and can reflect a phylogenetic signal, common biochemical pathways, or both. More important for this study, clustering can help to identify allomone targets. We herein compare common arthropod allomones with known vertebrate trigeminal irritants. We argue that the degree of overlap between these two groups of compounds indicates that chemesthesis was an important determining factor in the evolution of many arthropod allomones. The multidimensional scaling methods used may also allow the identification of new irritant receptors.     

How well do the existing and proposed reserve networks represent vertebrate species in Chile?

Increasingly, biogeographical knowledge and analysis are playing a fundamental role in assessing the representativeness of biodiversity in protected areas, and in identifying critical areas for conservation. With almost 20% of the country assigned to protected areas, Chile is well above the conservation target (i.e. 10–12%) proposed by many international conservation organizations. Moreover, the Chilean government has recently proposed new conservation priority sites to improve the current protected area network. Here, we used all 653 terrestrial vertebrate species present in continental Chile to assess the performance of the existing and proposed reserve networks. Using geographical information systems, we overlaid maps of species distribution, current protected areas, and proposed conservation priority sites to assess how well each species is represented within these networks. Additionally, we performed a systematic reserve selection procedure to identify alternative conservation areas for expanding the current reserve system. Our results show that over 13% of the species are not covered by any existing protected area, and that 73% of Chilean vertebrate species can be considered partial gaps, with only a small fraction of their geographical ranges currently under protection. The coverage is also deficient for endemic (species confined to Chile) and threatened species. While the proposed priority sites do increase coverage, we found that there are still several gaps and these are not the most efficient choices. Both the gap analysis and the reserve selection analysis identified important areas to be added to the existing reserve system, mostly in northern and central Chile. This study underscores the need for a systematic conservation planning approach to redefine the conservation priority sites in order to maximize the representation of species, particularly endemic and threatened species.     

Taphonomy and taxonomy of a vertebrate microsite in the mid-Cretaceous (Albian–Cenomanian) Blackleaf Formation,southwest Montana

The vertebrate fauna of the Cretaceous Blackleaf Formation of southwest Montana remains largely undocumented. A microsite (BL1) discovered in the Flood Member in the Lima Peaks area, Montana, consists of a green siltstone and yields taxa previously unreported from the formation, including several dinosaurs: a hypsilophodont, dromaeosaurid, tyrannosauroid, hadrosaurid and an ankylosaurian. Non-dinosaurian taxa include goniopholidid and Bernissartia crocodilians; Glyptops, cf. chelydrid and other turtles and at least two neopterygiian fish. This diversity corresponds well with the fluvial–deltaic–estuarine environment interpreted for the uppermost unit of the Flood Member. Taphonomic data and sedimentologic relationships suggest that this assemblage represents a floodplain depression accumulation. Comparisons with contemporaneous faunas from around the Western Interior of the USA suggest a remarkably consistent faunal makeup, at least at the family level, existed across western North America in the mid-Cretaceous.     

Review: Time–space translation regulates trunk axial patterning in the early vertebrate embryo

Here, we review a recently discovered developmental mechanism. Anterior–posterior positional information for the vertebrate trunk is generated by sequential interactions between a timer in the early non-organiser mesoderm and the Spemann organiser. The timer is characterised by temporally colinear activation of a series of Hox genes in the early ventral and lateral mesoderm (i.e., the non-organiser mesoderm) of the Xenopus gastrula. This early Hox gene expression is transient, unless it is stabilised by signals from the Spemann organiser. The non-organiser mesoderm (NOM) and the Spemann organiser undergo timed interactions during gastrulation which lead to the formation of an anterior–posterior axis and stable Hox gene expression. When separated from each other, neither non-organiser mesoderm nor the Spemann organiser is able to induce anterior–posterior pattern formation of the trunk. We present a model describing that NOM acquires transiently stable hox codes and spatial colinearity after involution into the gastrula and that convergence and extension then continually bring new cells from the NOM within the range of organiser signals that cause transfer of the mesodermal pattern to a stable pattern in neurectoderm and thereby create patterned axial structures. In doing so, the age of the non-organiser mesoderm, but not the age of the organiser, defines positional values along the anterior–posterior axis. We postulate that the temporal information from the non-organiser mesoderm is linked to mesodermal Hox expression. The role of the organiser was investigated further and this turns out to be only the induction of neural tissue. Apparently, development of a stable axial hox pattern requires neural hox patterning.     

Are dendrites in Drosophila homologous to vertebrate dendrites?

Dendrites represent arborising neurites in both vertebrates and invertebrates. However, in vertebrates, dendrites develop on neuronal cell bodies, whereas in higher invertebrates, they arise from very different neuronal structures, the primary neurites, which also form the axons. Is this anatomical difference paralleled by principal developmental and/or physiological differences? We address this question by focussing on one cellular model, motorneurons of Drosophila and characterise the compartmentalisation of these cells. We find that motorneuronal dendrites of Drosophila share with typical vertebrate dendrites that they lack presynaptic but harbour postsynaptic proteins, display calcium elevation upon excitation, have distinct cytoskeletal features, develop later than axons and are preceded by restricted localisation of Par6-complex proteins. Furthermore, we demonstrate in situ and culture that Drosophila dendrites can be shifted from the primary neurite to their soma, i.e. into vertebrate-like positions. Integrating these different lines of argumentation, we propose that dendrites in vertebrates and higher invertebrates have a common origin, and differences in dendrite location can be explained through translocation of neuronal cell bodies introduced during the evolutionary process by which arthropods and vertebrates diverged from a common urbilaterian ancestor. Implications of these findings for studies of dendrite development, neuronal polarity, transport and evolution are discussed.     

Interaction between the main components of the vertebrate retinal rod phototransduction system in solutions of detergent n-nonyl-β-D-glucoside

cGMP-Specific phosphodiesterase (PDE6) is the key enzyme of the phototransduction system of vertebrate retinal rod outer segments (ROS). The properties of PDE in extracts prepared by solubilization of bovine ROS in a high concentration (0.5% w/v) of detergent n-nonyl-β-D-glucoside (NG) and following centrifugation (ROS-NG) have been studied. Basal PDE activity of the preparations was low, but it greatly (>50-fold) increased (up to ∼20 μmol cGMP hydrolyzed/min per mg rhodopsin (R)) in the presence of trypsin. In bleached GTPγS-containing preparations the specific PDE activity was dependent on ROS-NG concentration and was half-maximal at about 0.8 μM of ROS G protein transducin (Gt). In dark-adapted GTPγS-containing ROS-NG preparations bleaching of 0.2% of the rhodopsin resulted in half-maximal PDE activation. The same result was obtained when PDE in dark-adapted ROS-NG preparations was activated by addition of a highly purified bleached rhodopsin solubilized by 0.5% solution of NG. The results demonstrate that the presence of NG has no significant influence either on the properties of the main ROS phototrans-duction system elements (R, Gt and PDE) or on the interaction between photoactivated R and Gt and suggest that the detergent NG can be used for crystallization of the rhodopsin-transducin complex.     

Head-tail patterning of the vertebrate embryo: one, two or many unresolved problems?

When, where and how is the head-tail axis of the embryo set up during development? These are such fundamental and intensely studied questions that one might expect them to have been answered long ago. Not so; we still understand very little about the cellular or molecular mechanisms that lead to the orderly arrangement of body elements along the head-tail axis in vertebrates. In this paper, we outline some of the major outstanding problems and controversies and try to identify some reasons why it has been so difficult to resolve this important issue.