Creating effective poster presentations: AMEE Guide no. 40.

Poster presentations have become an important part of professional meetings and are recognized as valuable tools for teaching and assessment. An effective poster is a visual communication tool that will help you engage colleagues in conversation, convey your main point to large numbers of people, and advertise your work. An effective poster is a highly condensed version of a research paper constructed primarily of visual displays of data with just enough supporting text to provide context, interpretation, and conclusions.

Ephrin-A5 exerts positive or inhibitory effects on distinct subsets of EphA4-positive motor neurons.

Eph receptor tyrosine kinases and ephrins are required for axon patterning and plasticity in the developing nervous system. Typically, Eph-ephrin interactions promote inhibitory events; for example, prohibiting the entry of neural cells into certain embryonic territories. Here, we show that distinct subsets of motor neurons that express EphA4 respond differently to ephrin-A5.

Long-distance cue from emerging dermis stimulates neural crest melanoblast migration.

Neural crest melanoblasts display unique navigational abilities enabling them to colonize the dorsal path between ectoderm and somite. One signal shown here to elicit melanoblast migration is a chemotactic cue supplied by the emerging dermis. Until dermis emerges, melanoblasts fail to enter the dorsal path.

Three functionally distinct adhesions in filopodia: shaft adhesions control lamellar extension.

In this study, adhesions on individual filopodial shafts were shown to control veil (lamellar) advance and to be modulated by guidance cues. Adhesions were detected in individual filopodia of sensory growth cones using optical recordings, adhesion markers, and electron microscopy. Veils readily advanced along filopodia lacking shaft adhesions but rarely advanced along filopodia displaying shaft adhesions.

Filopodial initiation and a novel filament-organizing center, the focal ring.

This study examines filopodial initiation and implicates a putative actin filament organizer, the focal ring. Filopodia were optically recorded as they emerged from veils, the active lamellar extensions of growth cones. Motile histories revealed three events that consistently preceded filopodial emergence: an influx of cytoplasm into adjacent filopodia, a focal increase in phase density at veil margins, and protrusion of nubs that transform into filopodia.

Identification of an invariant response: stable contact with schwann cells induces veil extension in sensory growth cones.

Growth cones sense cues by filopodial contact, but how their motility is altered by contact remains unclear. Although contact could alter motile dynamics in complex ways, our analysis shows that stable contact with Schwann cells induces motility changes that are remarkably discrete and invariant. Filopodial contact invariably induces local veil extension.

Contact with isolated sclerotome cells steers sensory growth cones by altering distinct elements of extension.

During pathfinding, growth cones respond to guidance cues by altering their motility. This study shows that motile responses can be highly specific: filopodial contact with two different, physiologically relevant cells differentially alters discrete elements of motility. With each cell type, the responses to contact are invariant.

Cellular interactions that guide sensory and motor neurites identified in an embryo slice preparation.

We used cultured cross sections ("slices") of avian embryos to identify interactions that guide neurites during their encounters with seven tissues that impose a stereotyped gross anatomical nerve pattern. We show that cultured slices retain tissue morphology, molecular distribution patterns, and guidance cues. They also allow us to directly visualize responses of labeled sensory and motor neurons deposited on the slice's surface.

Specifying the target identity of motoneurons.

In the vertebrate spinal cord, motoneurons are clustered into longitudinal columns in agreement with the targets they innervate. Motoneurons within each column acquire properties early in development that ensure their axons navigate to appropriate targets, but how this target identity is specified is unknown. Recently, Tsuchida et al.

Neural crest cells prefer the myotome's basal lamina over the sclerotome as a substratum.

Anterior sclerotome is presumed to be the only somitic tissue that guides neural crest cells as they migrate ventrally. In contrast, we report here that crest cells prefer the myotome's basal lamina over the sclerotome as a substratum. This conclusion stems from four observations.

Glycoconjugates mark a transient barrier to neural crest migration in the chicken embryo.

We report that two molecular markers correlate with a transient inhibition of neural crest cell entry into the dorsolateral path between the ectoderm and the somite in the avian embryo. During the period when neural crest cells are excluded from the dorsolateral path, both peanut agglutinin lectin (PNA)-binding activity and chondroitin-6-sulfate (C6S) immunoreactivity are expressed within this path. Both markers decline as neural crest cells enter.

Contact-mediated mechanisms of motor axon segmentation.

In the chick embryo, the segmental pattern of motor outgrowth depends on guidance cues provided by sclerotome cells. Motor axons preferentially invade the anterior sclerotome but avoid the posterior sclerotome. To determine how motor growth cone motility is influenced by these cells, we used videomicroscopy to analyze the behavior of motor growth cones as they confronted identified sclerotome cells in vitro.

Descriptive and experimental analysis of the dispersion of neural crest cells along the dorsolateral path and their entry into ectoderm in the chick embryo.

We have characterized the dispersion of neural crest cells along the dorsolateral path in the trunk of the chicken embryo and experimentally investigated the control of neural crest cell entry into this path. The distribution of putative neural crest cells was analyzed in plastic sections of embryos that had been incubated for 24 hr in HNK-1 antibody, a procedure that we show successfully labels neural crest cells in the dorsolateral path and ectoderm. In accord with earlier observations, crest cells delay entering the dorsolateral path until a day or more after their counterparts have colonized the ventral path.

Peanut agglutinin and chondroitin-6-sulfate are molecular markers for tissues that act as barriers to axon advance in the avian embryo.

Axon outgrowth between the spinal cord and the hindlimb of the chick embryo is constrained by three tissues that border axon pathways. Growth cones turn to avoid the posterior sclerotome, perinotochordal mesenchyme, and pelvic girdle precursor during normal development and after experimental manipulation. We wanted to know if these functionally similar barriers to axon advance also share a common molecular composition.

Ultrastructural and morphometric analysis of the separation of two thigh muscles in the chick.

Limb muscles separate from one another in a complex but highly stereotyped sequence and spatial pattern. The process of separation is characterized by the progression of a region of increased extracellular space, the cleavage zone, along the proximodistal axis between the individual muscle anlagen. We analyzed ultrastructurally the muscles and cleavage zone during the separation of two representative muscles, the developing sartorius and iliotibialis in the chick thigh, to establish an accurate baseline for an analysis of the mechanisms of separation.

Spatial and temporal patterns of muscle cleavage in the chick thigh and their value as criteria for homology.

Regions of lower cell density, called cleavage zones, emerge within the dorsal and ventral muscle masses in the vertebrate limb to separate distinct muscles. In the chick thigh, the stereotyped patterns of separation have been broadly outlined, but differences in interpretation exist because no criteria for separation have been defined, and the tissues of the limb are indistinct early in development. We have examined the cleavage process using modern applications of light microscopy and immunocytochemistry to completely detail the spatial and temporal progression of cleavage in stage 27-32 embryos.

Cells and cell-interactions that guide motor axons in the developing chick embryo.

A considerable challenge confronts any developing neuron. Before it can establish a functional and specific connection, it must extend an axon over tens and sometimes hundreds of microns through a complex and mutable environment to reach one out of many possible destinations. The field of axonal guidance concerns the control of this navigation process.

Distribution and projection pattern of motoneurons that innervate hindlimb muscles in the quail.

We characterized the motoneuron pool positions and projection patterns in the embryonic quail hindlimb and compared them to those in the chick to determine the degree of similarity and to form a baseline for future chimeric experiments. We find that the most similar parameters of pool position correlate with the major axonal pathway choices. First, the medial-lateral pool position, which is highly conserved among birds and mammals, is identical in the quail and chick and correlates with the dorsal-ventral pathway choice, the first and least plastic of the choices within the limb.

The perinotochordal mesenchyme acts as a barrier to axon advance in the chick embryo: implications for a general mechanism of axonal guidance.

To test the hypothesis that the perinotochordal mesenchyme (the sclerotome ventral to the spinal nerve pathway) is a barrier to axonal advance in the chick embryo, we determined whether axons directly confronted with perinotochordal mesenchyme would turn to avoid it. The initial direction of motor axon outgrowth was altered by rotating the right half of the neural tube after deleting the left half. Perinotochordal mesenchyme was identified histologically or by peanut agglutinin (PNA) binding.

Different subsets of axonal guidance cues are essential for sensory neurite outgrowth to cutaneous and muscle targets in the dorsal ramus of the embryonic chick.

The dorsal ramus nerve diverges dorsally from each spinal nerve to innervate the epaxial muscle and dermis that are derived in situ from each dermamyotome. The outgrowth of both the sensory and motor components of this nerve are sensitive to the proximity of the dermamyotome. Motoneurons display a direct target response that is not dependent upon the concurrent outgrowth of sensory neurites (Tosney: Dev.

A hierarchy of determining factors controls motoneuron innervation. Experimental studies on the development of the plantaris muscle (PL) in avian chimeras.

Quail leg buds were grafted in place of chick leg buds or chick wing buds and vice versa at stages 18 to 21 after colonization by muscle precursor cells had been completed. Motor endplate pattern in the plantaris muscle of the grafts was analyzed before hatching by means of esterase and acetylcholinesterase staining techniques. Muscle fibre types were made visual using the myosin ATPase reaction.