The early development of the primary sensory neurones in an amphibian embryo: a scanning electron microscope study

Development ◽  
1983 ◽  
Vol 75 (1) ◽  
pp. 49-66
Author(s):  
J. S. H. Taylor ◽  
Alan Roberts
Keyword(s):  
Basal Lamina ◽  
Outer Surface ◽  
Sensory System ◽  
Epidermal Cells ◽  
Ependymal Cells ◽  
Growth Substrate ◽  
Amphibian Embryo ◽  
Scanning Electron Microscope Study ◽  
Larval Stages ◽  
Xenopus Laevis Embryos

We have described the development of the primary sensory system of the trunk region of Xenopus laevis embryos from larval stages 21 to 32. The system is based upon Rohon-Beard and extramedullary cells, which have central axons forming a dorsolateral spinal tract and peripheral neurites which innervate the skin. The pioneer axons of the central tract grow along the outer surface of the cord at stage 22. These pioneer axons may be used by secondary axons as a growth substrate. As the tract forms it is covered by the radially expanding distal processes, ‘end feet’, of the ependymal cells of the cord. Cell bodies of the extramedullary cells bulge out of the cord surface, and are first seen between the newly segmented myotomes, at stage 24. Peripheral neurites from these extramedullary cells grow out laterally from the cord. The Rohon-Beard cells, located within the cord, produce similar peripheral neurites which grow laterally with the extramedullary cell neurites, using them as a substrate. The neurites form bundles which coincide with the intermyotomes and are periodically spaced. The growth cones of these neurites contact the outer surface of the myotomes and proceed ventrally, first on the myotomes and then on the basal lamina of the skin. ‘Pioneer’ neurites are used by later neurites as a growth substrate, but not to the exclusion of all other substrates. The neurites form a plexus on the skin's basal lamina and contact the underlying epidermal cells through holes in the basal lamina. These holes occur in positions over the intercellular boundaries of the epidermal cells.

Effects of cadmium-enriched sediment on fish and amphibian embryo-larval stages

1984 ◽  
Vol 8 (4) ◽  
pp. 378-387 ◽  
Author(s):  
Paul C. Francis ◽  
Wesley J. Birge ◽  
Jeffrey A. Black
Keyword(s):  
Amphibian Embryo ◽  
Larval Stages

scholarly journals Membrane protein redistribution during Xenopus first cleavage.

1986 ◽  
Vol 102 (6) ◽  
pp. 2176-2184 ◽  
Author(s):  
T J Byers ◽  
P B Armstrong
Keyword(s):  
Leading Edge ◽  
Surface Proteins ◽  
Cleavage Furrow ◽  
Initial Surface ◽  
Contractile Ring ◽  
Animal Pole ◽  
Amphibian Embryo ◽  
Carbon Particles ◽  
Later Phase ◽  
Xenopus Laevis Embryos

A large increase in surface area must accompany formation of the amphibian embryo first cleavage furrow. The additional membrane for this areal expansion has been thought to be provided entirely from cytoplasmic stores during furrowing. We have radioiodinated surface proteins of fertilized, precleavage Xenopus laevis embryos and followed their redistribution during first cleavage by autoradiography. Near the end of first cleavage, membrane of the outer, pigmented surface of the embryo and a short band of membrane at the leading edge of the furrow displayed a high silver grain density, but the remainder of the furrow membrane was lightly labeled. The membrane of the cleavage furrow is thus mosaic in character; the membrane at the leading edge originates in part from the surface of the zygote, but most of the membrane lining the furrow walls is derived from a source inaccessible to surface radioiodination. The furrow membrane adjacent to the outer, pigmented surface consistently showed a very low silver grain density and was underlain by large membranous vesicles, suggesting that new membrane derived from cytoplasmic precursors is inserted primarily in this location, at least during the later phase of cleavage. Radioiodinated membrane proteins and surface-attached carbon particles, which lie in the path of the future furrow, contract toward the animal pole in the initial stages of cleavage while markers in other regions do not. We suggest that the domain of heavily labeled membrane at the leading edge of the definitive furrow contains the labeled elements that are gathered at the animal pole during the initial surface contraction and that they include membrane anchors for the underlying contractile ring of microfilaments.

scholarly journals Characteristics of the surface of the epidermis in floral nectaries and the receptacle of mountain ash (Sorbus aucuparia L.)

2012 ◽  
Vol 60 (2) ◽  
pp. 23-30
Author(s):  
Agata Konarska
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Outer Surface ◽  
Flower Development ◽  
Epidermal Cells ◽  
Sorbus Aucuparia ◽  
Mountain Ash ◽  
Floral Nectaries ◽  
Scanning Electron

The structure of receptacular surfaces of floral nectaries at two flowering stages and the structure of the outer surface of the receptacle of <i>Sorbus aucuparia</i> were investigated using scanning electron microscopy. Changes in the development of the cuticular epithelium of the nectary epidermis and differences in the degree of aperture of stomata were observed. Increased undulation of the gland surface was found during flower development. Numerous stomata were situated slightly below the level of epidermal cells of the nectary. At the pollination stage, open pores or pores surrounded by the cuticular epithelium were observed, as well as covered by dried secretion. Dried nectar in the form of patches was also visible on the surface of the gland. Stomata of the outer surface of the receptacle were located on protrusions and surrounded by the cuticular epithelium.

Dynamics of the control of body pattern in the development of Xenopus laevis

Development ◽  
1985 ◽  
Vol 88 (1) ◽  
pp. 85-112
Author(s):  
Jonathan Cooke ◽  
John A. Webber
Keyword(s):  
Body Position ◽  
Posterior Part ◽  
Frontal Plane ◽  
Positional Information ◽  
Bilateral Symmetry ◽  
The Body ◽  
Fate Map ◽  
Amphibian Embryo ◽  
Larval Stages ◽  
Body Pattern

Xenopus embryos have been selected in which the second cleavage is occuring in a frontal plane, i.e one tending to lie at right angles to the prospective plane of bilateral symmetry for the body pattern. Some of these have been used to deduce a map of the disposition of materials for the normal mesodermal pattern (the normal ‘fate map’) by injecting blastomeres to found fluorescently marked clones from 4- to 32-cell stages. Other such 4-cell embryos have been separated into two isolates across this second cleavage; in fate-map terms, prospective dorsoanterior and posterior isolates. These have been allowed to develop to control axial larval stages, with examination of the time schedule of their gastrulation movements in relation to cofertilized whole controls. The patterns of mesoderm produced have been examined and interpreted in the light of quantitative knowledge about the normal pattern, and our current understanding of the map. A meaningful fate map exists for the egg material even at this early, essentially acellular stage, and it differs appreciably from what might have been expected in view of that traditionally shown for early gastrula stages. The patterns developed in the isolates show that at least in many eggs, widespread information that positively specifies material as to its body position is available from at most 1 h after the events that give rise to bilateral symmetry upon fertilization. This information usually leads to a mosaic development of the appropriate mesodermal part-pattern in dorsoanterior isolates, and frequently allows development that approximates to this in the reciprocal posterior part. Regulation, i.e. the replacement of removed information to specify a development more complete than the normal contribution in isolates, is not observed. The results suggest a revision of former claims for regulative ability in at least this amphibian embryo. They also imply that systems for ascribing position value (positional information) to early embryonic tissue can be diverse in dynamics, even among embryos whose body plans are obviously homologous as are those of vertebrates.

Scanning electron microscope study of the development of mandibular structure and the molar surface morphology of Branchinella maduraiensis and Streptocephalus dichotomus (Crustacea, Anostraca)

2006 ◽  
Vol 84 (9) ◽  
pp. 1248-1262 ◽  
Author(s):  
Chinavenmeni S. Velu ◽  
Natesan Munuswamy
Keyword(s):  
Surface Morphology ◽  
Developmental Stages ◽  
Gradual Transition ◽  
Mandibular Movement ◽  
Scanning Electron Microscope Study ◽  
Larval Stages ◽  
Ephemeral Pools ◽  
Molar Morphology ◽  
Further Development ◽  
Scanning Electron

In the present study, the molar surface morphology of Streptocephalus dichotomus Baird, 1860 and Branchinella maduraiensis Raj, 1961 is analyzed and correlated with the distribution of these species in ephemeral pools. The larval stages of S. dichotomus are characterized by scanning electron microscopy in relation to their feeding physiology, which shows their morphological complexity during developmental stages. The larval mandible consists of a coxa with a three-segmented palp, and further development leads to its gradual transition into the adult mandible. Muscles involved in mandibular movement exhibit rotatory and counter-rotatory movement, which enhances the grinding of food materials. Analysis of the molar surface morphology of B. maduraiensis and S. dichotomus reveals that the mandibles are asymmetrical. Detailed analysis of the topography of the molar illustrates specific structural differences between the species. Gut content analysis also perfectly matches the molar morphology of these species, confirming that B. maduraiensis handles zooplankton more preferentially than S. dichotomus. Our investigation of these fairy shrimps provides information on their molar surface morphology and feeding biology, which increases the understanding of their coexistence.

A scanning electron microscope study of the development of a peripheral sensory neurite network

Development ◽  
1982 ◽  
Vol 69 (1) ◽  
pp. 237-250
Author(s):  
Alan Roberts ◽  
J. S. H. Taylor
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Basal Lamina ◽  
Growth Cone ◽  
Growth Cones ◽  
Sensory Innervation ◽  
Scanning Electron Microscope Study ◽  
Scanning Electron

The formation of the sensory neurite plexus on the basal lamina of trunk skin in Xenopus embryos has been examined using the scanning electron microscope. It is formed by Rohon-Beard and extramedullary neurons which provide the first sensory innervation of the skin. By observing the distribution of growth cones on the inside surface of the skin of embryos at different ages, the development of the plexus has been followed and related to the development of sensitivity to sensory stimulation. The general features of the plexus are illustrated using a photomontage taken at × 1100. Measurements on neurites from this, and of growth cone orientations demonstrate a general ventral growth pattern with some small regional variations. Interactions of neurites within the plexus are examined. Neurites meeting at shallow angles tend to fasciculate, whilethose meeting at close to 90° tend to cross each other. Angles of incidence and separation of neurites show few angles less than 30°, which suggests that active adjustments occur after a growth cone meets or leaves another neurite. The observations allow comparison of behaviour of growing neurites in vivo and in vitro. Our evidence suggests that adhesion between growth cones and neurites is stronger than that between growth cones and the basal lamina of the skin.

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