Early development of Ensatina eschscholtzii: an amphibian with a large, yolky egg

<p>Abstract</p> <p>Background</p> <p>Comparative analyses between amphibians, concentrating on the cellular mechanisms of morphogenesis, reveal a large variability in the early developmental processes that were thought to be conserved during evolution. Increased egg size is one factor that could have a strong effect on early developmental processes such as cleavage pattern and gastrulation. Salamanders of the family Plethodontidae are particularly appropriate for such comparative studies because the species have eggs of varying size, including very large yolky eggs.</p> <p>Results</p> <p>In this paper, we describe for the first time the early development (from fertilization through neurulation) of the plethodontid salamander <it>Ensatina eschscholtzii</it>. This species has one of the largest eggs known for an amphibian, with a mean ± SD diameter of 6 ± 0.43 mm (range 5.3-6.9; n = 17 eggs). Cleavage is meroblastic until approximately the 16-cell stage (fourth or fifth cleavage). At the beginning of gastrulation, the blastocoel roof is one cell thick, and the dorsal lip of the blastopore forms below the equator of the embryo. The ventral lip of the blastopore forms closer to the vegetal pole, and relatively little involution occurs during gastrulation. Cell migration is visible through the transparent blastocoel roof of the gastrula. At the end of gastrulation, a small archenteron spreading dorsally from the blastopore represents the relatively small and superficial area of the egg where early embryonic axis formation occurs. The resulting pattern is similar to the embryonic disk described for one species of anuran.</p> <p>Conclusions</p> <p>Comparisons with the early development of other species of amphibians suggest that an evolutionary increase in egg size can result in predictable changes in the patterns and rate of early development, but mainly within an evolutionary lineage.</p

Vital dye labelling of Xenopus laevis trunk neural crest reveals multipotency and novel pathways of migration

Although the Xenopus embryo has served as an important model system for both molecular and cellular studies of vertebrate development, comparatively little is known about its neural crest. Here, we take advantage of the ease of manipulation and relative transparency of Xenopus laevis embryos to follow neural crest cell migration and differentiation in living embryos. We use two techniques to study the lineage and migratory patterns of frog neural crest cells: (1) injections of DiI or lysinated rhodamine dextran (LRD) into small populations of neural crest cells to follow movement and (2) injections of LRD into single cells to follow cell lineage. By using non-invasive approaches that allow observations in living embryos and control of the time and position of labelling, we have been able to expand upon the results of previous grafting experiments. Migration and differentiation of the labelled cells were observed over time in individual living embryos, and later in sections to determine precise position and morphology. Derivatives populated by the neural crest are the fins, pigment stripes, spinal ganglia, adrenal medulla, pronephric duct, enteric nuclei and the posterior portion of the dorsal aorta. In the rostral to mid-trunk levels, most neural crest cells migrate along two paths: a dorsal pathway into the fin, followed by presumptive fin cells, and a ventral pathway along the neural tube and notochord, followed by presumptive pigment, sensory ganglion, sympathetic ganglion and adrenal medullary cells. In the caudal trunk, two additional paths were noted. One group of cells moves circumferentially within the fin, in an arc from dorsal to ventral; another progresses ventrally to the anus and subsequently populates the ventral fin. By labelling individual precursor cells, we find that neural tube and neural crest cells often share a common precursor. The majority of clones contain labelled progeny cells in the dorsal fin. The remainder have progeny in multiple derivatives including spinal ganglion cells, pigment cells, enteric cells, fin cells and/or neural tube cells in all combinations, suggesting that many premigratory Xenopus neural crest precursors are multipotent

Segmental migration of trunk neural crest: time-lapse analysis reveals a role for PNA-binding molecules

Trunk neural crest cells migrate through the somites in a striking segmental fashion, entering the rostral but not caudal sclerotome, via cues intrinsic to the somites. Attempts to define the molecular bases of these cues have been hampered by the lack of an accessible assay system. To examine trunk neural crest migration over time and to perturb candidate guiding molecules, we have developed a novel explant preparation. Here, we demonstrate that trunk regions of the chicken embryo, placed in explant culture, continue to develop apparently normally for 2 days. Neural crest cells, recognized by prelabeling with DiI or by poststaining with the HNK-1 antibody, migrate in the somites of the explants in their typical segmental pattern. Furthermore, this paradigm allows us to follow trunk neural crest migration in situ for the first time using low-light-level videomicroscopy. The trajectories of individual neural crest cells were often complex, with cells migrating in an episodic mode encompassing forward, backward and lateral movements. Frequently, neural crest cells migrated in close-knit groups of 2–4 cells, moving at mean rates of migration of 10–14 µm/hour. Treatment of the explants with the lectin peanut agglutinin (PNA) both slowed the rate and altered the pattern of neural crest migration. Neural crest cells entered both the rostral and caudal halves of the sclerotome with mean rates of migration ranging from 6 to 13 µm/hour. These results suggest that peanut agglutinin-binding molecules are required for the segmental patterning of trunk neural crest migration. Because this approach permits neural crest migration to be both observed and perturbed, it offers the promise of more direct assays of the factors that influence neural crest development

XASH-3, a novel Xenopus achaete-scute homolog, provides an early marker of planar neural induction and position along the mediolateral axis of the neural plate

We have isolated a novel Xenopus homolog of the Drosophila achaete-scute genes, called XASH-3. XASH-3 expression is neural specific and is detected as early as stage 11 1/2, making it one of the earliest markers of neural induction so far described. Moreover, XASH-3 expression within the neural plate is regionally restricted. Transverse bands of XASH-3 mRNA mark discrete positions along the anteroposterior axis, while longitudinal bands mark a discrete position along the mediolateral axis. This latter site of XASH-3 expression appears to demarcate the prospective sulcus limitans, a boundary zone that later separates the functionally distinct dorsal (alar) and ventral (basal) regions of the spinal cord. In sandwich explants lacking any underlying mesoderm, XASH-3 is expressed in longitudinal stripes located lateral to the midline. This provides the first indication that planar or midline-derived inductive signals are sufficient to establish at least some aspects of positional identity along the mediolateral axis of the neural plate. By contrast, the transverse stripes of XASH-3 expression are not detected, suggesting that this aspect of anteroposterior neural pattern is lost or delayed in the absence of vertically passed signals. The restricted mediolateral expression of XASH-3 suggests that mediolateral patterning of the neural plate is an early event, and that this regionalization can be achieved in the absence of inducing signals derived from underlying mesoderm

Green Fluorescent Protein in the sea urchin: new experimental approaches to transcriptional regulatory analysis in embryos and larvae

The use of Green Fluorescent Protein (GFP) as a reporter for expression transgenes opens the way to several new experimental strategies for the study of gene regulation in sea urchin development. A GFP coding sequence was associated with three different previously studied cis-regulatory systems, viz those of the SM50 gene, expressed in skeletogenic mesenchyme, the CyIIa gene, expressed in archenteron, skeletogenic and secondary mesenchyme, and the Endo16 gene, expressed in vegetal plate, archenteron and midgut. We demonstrate that the sensitivity with which expression can be detected is equal to or greater than that of whole-mount in situ hybridization applied to detection of CAT mRNA synthesized under the control of the same cis-regulatory systems. However, in addition to the important feature that it can be visualized nondestructively in living embryos, GFP has other advantages. First, it freely diffuses even within fine cytoplasmic cables, and thus reveals connections between cells, which in sea urchin embryos is particularly useful for observations on regulatory systems that operate in the syncytial skeletogenic mesenchyme. Second, GFP expression can be dramatically visualized in postembryonic larval tissues. This brings postembryonic larval developmental processes for the first time within the easy range of gene transfer analyses. Third, GFP permits identification and segregation of embryos in which the clonal incorporation of injected DNA has occurred in any particular desired region of the embryo. Thus, we show explicitly that, as expected, GFP transgenes are incorporated in the same nuclei together with other transgenes with which they are co-injected

Characterization of the brain functional architecture of psychostimulant withdrawal using single-cell whole brain imaging

Numerous brain regions have been identified as contributing to addiction-like behaviors, but unclear is the way in which these brain regions as a whole lead to addiction. The search for a final common brain pathway that is involved in addiction remains elusive. To address this question, we used male C57BL/6J mice and performed single-cell whole-brain imaging of neural activity during withdrawal from cocaine, methamphetamine, and nicotine. We used hierarchical clustering and graph theory to identify similarities and differences in brain functional architecture. Although methamphetamine and cocaine shared some network similarities, the main common neuroadaptation between these psychostimulant drugs was a dramatic decrease in modularity, with a shift from a cortical- to subcortical-driven network, including a decrease in total hub brain regions. These results demonstrate that psychostimulant withdrawal produces the drug-dependent remodeling of functional architecture of the brain and suggest that the decreased modularity of brain functional networks and not a specific set of brain regions may represent the final common pathway that leads to addiction

Wnt-Dependent Epithelial Transitions Drive Pharyngeal Pouch Formation

The pharyngeal pouches, which form by budding of the foregut endoderm, are essential for segmentation of the vertebrate face. To date, the cellular mechanism and segmental nature of such budding have remained elusive. Here, we find that Wnt11r and Wnt4a from the head mesoderm and ectoderm, respectively, play distinct roles in the segmental formation of pouches in zebrafish. Time-lapse microscopy, combined with mutant and tissue-specific transgenic experiments, reveal requirements of Wnt signaling in two phases of endodermal epithelial transitions. Initially, Wnt11r and Rac1 destabilize the endodermal epithelium to promote the lateral movement of pouch-forming cells. Next, Wnt4a and Cdc42 signaling induce the rearrangement of maturing pouch cells into bilayers through junctional localization of the Alcama immunoglobulin-domain protein, which functions to restabilize adherens junctions. We propose that this dynamic control of epithelial morphology by Wnt signaling may be a common theme for the budding of organ anlagen from the endoderm

Characterization of the brain functional architecture of psychostimulant withdrawal using single-cell whole brain imaging

Numerous brain regions have been identified as contributing to addiction-like behaviors, but unclear is the way in which these brain regions as a whole lead to addiction. The search for a final common brain pathway that is involved in addiction remains elusive. To address this question, we used male C57BL/6J mice and performed single-cell whole-brain imaging of neural activity during withdrawal from cocaine, methamphetamine, and nicotine. We used hierarchical clustering and graph theory to identify similarities and differences in brain functional architecture. Although methamphetamine and cocaine shared some network similarities, the main common neuroadaptation between these psychostimulant drugs was a dramatic decrease in modularity, with a shift from a cortical- to subcortical-driven network, including a decrease in total hub brain regions. These results demonstrate that psychostimulant withdrawal produces the drug-dependent remodeling of functional architecture of the brain and suggest that the decreased modularity of brain functional networks and not a specific set of brain regions may represent the final common pathway that leads to addiction

Low intensity vs. self-guided Internet-delivered psychotherapy for major depression: A multicenter, controlled, randomized study

Background: Major depression will become the second most important cause of disability in 2020. Computerized cognitive-behaviour therapy could be an efficacious and cost-effective option for its treatment. No studies on cost-effectiveness of low intensity vs self-guided psychotherapy has been carried out. The aim of this study is to assess the efficacy of low intensity vs self-guided psychotherapy for major depression in the Spanish health system. Methods: The study is made up of 3 phases: 1.- Development of a computerized cognitive-behaviour therapy for depression tailored to Spanish health system. 2.- Multicenter controlled, randomized study: A sample (N=450 patients) with mild/moderate depression recruited in primary care. They should have internet availability at home, not receive any previous psychological treatment, and not suffer from any other severe somatic or psychological disorder. They will be allocated to one of 3 treatments: a) Low intensity Internet-delivered psychotherapy + improved treatment as usual (ITAU) by GP, b) Self-guided Internet-delivered psychotherapy + ITAU or c) ITAU. Patients will be diagnosed with MINI psychiatric interview. Main outcome variable will be Beck Depression Inventory. It will be also administered EuroQol 5D (quality of life) and Client Service Receipt Inventory (consume of health and social services). Patients will be assessed at baseline, 3 and 12 months. An intention to treat and a per protocol analysis will be performed. Discussion: The comparisons between low intensity and self-guided are infrequent, and also a comparative economic evaluation between them and compared with usual treatment in primary. The strength of the study is that it is a multicenter, randomized, controlled trial of low intensity and self-guided Internet-delivered psychotherapy for depression in primary care, being the treatment completely integrated in primary care setting

Impacto del tránsito en dos sistemas de siembra

Los sistemas productivos agrícolas presentan altos niveles de mecanización con tractores y máquinas cada vez más pesados. Como consecuencia, la compactación de los suelos es un problema emergente, dando como resultado el deterioro de la estructura de muchos suelos y la baja de los rendimientos productivos. El objetivo del presente trabajo fue evaluar el efecto de distintas intensidades de tráfico sobre dos condiciones de suelo: con labranza y bajo siembra directa, sometidos a diferentes intensidades de tráfico. Se compararon dos sistemas de siembra: suelo bajo siembra directa y suelo con labranza. Como subtratamientos se estudió la incidencia del pasaje repetido sobre la misma senda de un tractor de 6,4 Mg resultando en una, cinco y diez pasadas. Para cuantificar la compactación inducida se evaluaron la resistencia a la penetración, la densidad aparente y la profundidad de huella. Además se evaluó la compactación máxima resultante a través del test Proctor (1933). El suelo labrado resultó ser más compactable, presentando mayor profundidad de huella y menos resistencia a la penetración luego del tráfico. El suelo bajo siembra directa presentó una menor compactabilidad Proctor y una menor humedad óptima. Además, se encontró que este suelo tenía un mayor porcentaje de carbono total y de carbono particulado y mayor estabilidad estructural. El suelo bajo siembra directa fue capaz de almacenar más agua durante un periodo más prolongado. Hubo un comportamiento reológico diferente según el sistema de labranza. Los cambios en las propiedades físicas mesuradas resultaron más evidentes en el suelo labrado.Agricultural farm systems show high levels of mechanization using tractors and machines weighing more than formers. As a consequence, soil compaction is an emerging problem, resulting in the deterioration of the structure of many soils and low yields. The aim of this study was to evaluate the effect of different intensities of traffic on two conditions of soil: low tillage and direct seeding, under different traffic intensities. Two sowing systems were compared: direct seeding and tilled soil sowing. As subtreatments, multiple traffic intensities were applied using one, five and ten passes of a 6.4 Mg tractor. Induced soil compaction was assessed by penetration resistance, bulk density and rut depth. In addition the resulting maximum compaction was evaluated using Proctor Test (1933). Tilled soil was more compactable, showing more important rut depths and less penetration resistance after the traffic. The soil under reduced tillage presented lower Proctor compactness and lower optimum moisture. Furthermore, it was found that this soil had a higher percentage of total carbon and particulate carbon, and greater structural stability. The soil under no tillage was able to store more water for a longer period. There was a different rheological behavior under tillage system. The changes in physical properties were more evident in the tilled soil.EEA Cuenca del SaladoFil: Draghi, Laura. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Jorajuría Collazo, Daniel. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Sarena, Daniel Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Bailleres, Matias Andres. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado. Agencia de Extensión Rural Chascomus; ArgentinaFil: Melani, Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cuenca del Salado; ArgentinaFil: Castillo, José Manuel. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Cerisola, Cecilia. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Palancar, Telmo. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentin