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J Löfberg

Publications and source records attributed to J Löfberg.

9 recordsLinked to original sources
PubMed1990

Structural and compositional divergencies in the extracellular matrix encountered by neural crest cells in the white mutant axolotl embryo.

The skin of the white mutant axolotl larva is pigmented differently from that of the normal dark due to a local inability of the extracellular matrix (ECM) to support subepidermal migration of neural crest-derived pigment cell precursors. In the present study, we have compared the ECM of neural crest migratory pathways of normal dark and white mutant embryos ultrastructurally, immunohistochemically and biochemically to disclose differences in their structure/composition that could be responsible for the restriction of subepidermal neural crest cell migration in the white mutant axolotl. When examined by electron microscopy, in conjunction with computerized image analysis, the structural assembly of interstitial and basement membrane ECMs of the two embryos was found to be largely comparable. At stages of initial neural crest cell migration, however, fixation of the subepidermal ECM in situ with either Karnovsky-ruthenium red or with periodate-lysine-paraformaldehyde followed by ruthenium red-containing fixatives, revealed that fibrils of the dark matrix were significantly more abundant in associated electron-dense granules. This ultrastructural discrepancy of the white axolotl ECM was specific for the subepidermal region and suggested an abnormal proteoglycan distribution. Dark and white matrices of the medioventral migratory route of neural crest cells had a comparable appearance but differed from the corresponding subepidermal ECMs. Immunohistochemistry revealed only minor differences in the distribution of fibronectin, laminin, collagen types I, and IV, whereas collagen type III appeared differentially distributed in the two embryos. Chondroitin- and chondroitin-6-sulfate-rich proteoglycans were more prevalent in the white mutant embryo than in the dark, especially in the subepidermal space. Membrane microcarriers were utilized to explant site-specifically native ECM for biochemical analysis. Two-dimensional gel electrophoresis of these regional matrices revealed a number of differences in their protein content, principally in constituents of apparent molecular masses of 30-90,000. Taken together our observations suggest that local divergences in the concentration/assembly of low and high molecular mass proteins and proteoglycans of the ECM encountered by the moving neural crest cells account for their disparate migratory behavior in the white mutant axolotl.

Ambystoma↗
PubMed1990

The development of the larval pigment patterns in Triturus alpestris and Ambystoma mexicanum.

1. Melanophores and xanthophores are pigment cell derivatives of the NC. In amphibian embryos they migrate from their original position on the neural tube dorsally (into the dorsal fin) as well as laterally (between somites and epidermis) and arrange themselves into typical pigment patterns of the skin. We investigated pigment pattern formation in two species of tailed amphibians, Triturus alpestris (alpine newt) and Ambystoma mexicanum (Mexican axolotl). In larvae of T. alpestris alternating longitudinal stripes or bands of melanophores and xanthophores develop, whereas in larvae of A. mexicanum a barred pattern with alternating transverse bands of melanophores and xanthophores is formed. Iridophores, a third type of pigment cell, are present later in both species and therefore play no role during early larval pigment pattern development. Visibly differentiated melanophores and xanthophores can be distinguished from each other under the light microscope by their contents of black melanins and yellow pterins respectively. With the dopa reaction (indicates tyrosinase in melanophores), and ammonia treatment (stimulates pterin fluorescence in xanthophores), the pigment cell phenotypes can be visualized even before their normal visible differentiation. In the TEM, melanophores and xanthophores can be distinguished from each other by their morphologically distinct pigment organelles and in the SEM by their different surface structure. 2. Because of the NC origin of melanophores and xanthophores and the ease with which these cells can be demonstrated even before they are visible from outside, their different arrangements in Triturus and axolotl embryos offer suitable model systems for studying the migration, interaction and localization of NC derivatives in relation to specific environmental influences. The environment of NC cells are the neural tube, epidermis, somites and lateral plate mesoderm, and the subepidermal ECM, a network of collagen fibrils associated with glycosaminoglycans, proteoglycans and glycoproteins. 3. Development of the pigment pattern in T. alpestris: Melanophores and xanthophores start to leave the NC at stage 28, melanophores slightly earlier than xanthophores. Both cell types become scattered in the dorsolateral trunk. In contrast to melanophores in the axolotl, melanophores in T. alpestris cannot be demonstrated with the dopa reaction before they become visibly black. From stage 29+ onwards, melanophores start to accumulate in zones alongside the dorsal and lateral somite edges, where they form compact stripes later. Xanthophores can be demonstrated from stage 28+ onwards only with the SEM (by means of their specific surface structures) or with the fluorescence microscope (by means of their fluorescing pterins). At state 34, xanthophores become visible externally as yellow cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma↗
PubMed1989

Timing in the regulation of neural crest cell migration: retarded "maturation" of regional extracellular matrix inhibits pigment cell migration in embryos of the white axolotl mutant.

In larvae of the white axolotl mutant (Ambystoma mexicanum), contrary to normal dark ones, trunk pigmentation is restricted because the epidermis is unable to support subepidermal migration of pigment cells from the neural crest (NC). This study examines whether the subepidermal extracellular matrix (ECM) is the defective component which prevents pigment cell migration in the white embryo. We transplanted subepidermal ECM, adsorbed in vivo on membrane microcarriers, from and to white and dark embryos in various combinations. White embryos have demonstrated normal NC cell migration along the medioventral pathway, and in order to test the effects of medial ECM on subepidermal migration, this ECM was similarly transplanted. Carriers with ECM attached were inserted subepidermally in host embryos at a premigratory NC stage. Control carriers without ECM and carriers with subepidermal ECM from white donors did not affect NC cell migration in white or dark embryos. In contrast, subepidermal ECM from dark donors triggered NC cell migration in the subepidermal space of both white and dark hosts. Remarkably, subepidermal ECM from white donors which were older than those normally used also stimulated migration in embryos of both strains. Likewise, medial ECM from white donors elicited migration in white as well as dark hosts. Pigment cells occurred among those NC cells that were stimulated to migrate in response to contact with ECM on carriers. These results indicate that the subepidermal ECM of the white embryo is transiently defective as a substrate for pigment cell migration, implying that "maturation" of the ECM is retarded beyond the times during which pigment cells are able to respond. In contrast, the medial ECM of the white embryo appears to mature normally. These findings suggest that the effect of the d gene is expressed regionally through the subepidermal ECM during a limited period of development. Hence, the action of the d gene seems to retard ECM maturation, bringing it out of phase with the migratory capability of the pigment cells. We propose that such a shift in relative timing of the developmental phenomena involved inhibits pigment cell migration in embryos of the white axolotl mutant and, accordingly, that the restricted pigmentation of the mutant larva is generated through heterochrony.

Ambystoma mexicanum↗
PubMed1988

Local embryonic matrices determine region-specific phenotypes in neural crest cells.

Membrane microcarriers were used to determine the ability of regional extracellular matrices to direct neural crest cell differentiation in culture. Neural crest cells from the axolotl embryo responded to extracellular matrix material explanted from the subepidermal migratory pathway by dispersing and by differentiating into pigment cells. In contrast, matrix material from the presumptive site of dorsal root ganglia stimulated pronounced cell-cell association and neurotypic expression. Cell line segregation during ontogeny of the neural crest that leads to diversification into pigment cells of the skin or into elements of the peripheral nervous system appears to be controlled in part by local cell-matrix interactions.

Ambystoma mexicanum↗
PubMed1986

Promotion of chromatophore differentiation in isolated premigratory neural crest cells by extracellular matrix material explanted on microcarriers.

This study was undertaken to determine whether premigratory neural crest cells of the axolotl embryo differentiate autonomously into chromatophores, or whether stimuli from the environment, particularly from the extracellular matrix, are required for this process. Neural crest cells were excised from the dorsal part of the premigratory crest cord and cultured alone, either in a serum-free salt solution or in the presence of fetal calf serum (FCS), and together with explants of the neural tube or dorsal epidermis. A "microcarrier" technique was developed to assay the possible effects of subepidermal extracellular matrix (ECM) on chromatophore differentiation. ECM was adsorbed in vivo onto microcarriers prepared from Nuclepore filters, by inserting such carriers under the dorsolateral epidermis in the embryonic trunk. Neural crest cells were then cultured on the substrate of ECM deposited on the carriers. Melanophores were detected by DOPA incubation, revealing phenol oxidase activity, or by externally visible accumulation of melanin. Prospective xanthophores were visualized before they became overtly differentiated by alkali-induced pteridine fluorescence. Isolated premigratory neural crest cells did not transform autonomously into any of these phenotypes. Conversely, coculture with the neural tube or the dorsal epidermis, and also the initial presence or later addition of FCS during incubation, resulted in differentiation of neural crest cells into chromatophores. Both chromatophore phenotypes were also expressed on the ECM substrate deposited on the microcarriers. The results indicate that neural crest cells do not differentiate autonomously into melanophores and xanthophores, but that interactions with components of, or factors associated with the extra cellular matrix surrounding the premigratory neural crest and present along the dorsolateral migratory pathway are crucial for the expression of these chromatophore phenotypes in the embryo.

Ambystoma↗
PubMed1985

Stimulation of initial neural crest cell migration in the axolotl embryo by tissue grafts and extracellular matrix transplanted on microcarriers.

The present experiments were designed to test whether the onset of neural crest cell migration in the embryonic axolotl trunk is stimulated by surrounding tissues and their associated extracellular matrix (ECM). Tissue grafts, or embryonic ECM adsorbed in vivo onto inert "microcarriers" prepared from Nuclepore filters, were placed close to the premigratory neural crest cells, and the embryos were then incubated to a specific stage. The experiments were evaluated with light microscopy, SEM, and TEM. It was found that grafts from the dorsal epidermis were especially effective in locally stimulating initial neural crest cell migration in the region under the graft. The microcarrier experiments showed that the subepidermal ECM alone could initiate neural crest cell migration, implying that the ECM of the epidermal grafts was the stimulating factor. These results indicate that the premigratory neural crest cells along the trunk have migratory capability but that they need to be triggered from the environment, probably from the surrounding ECM, to start migration. It is proposed that ECM, as substrate for cell locomotion, initiates and regulates the onset of neural crest cell migration.

Ambystoma↗
PubMed1979

Granulocyte function during prophylaxis with doxycycline.

The influence of doxycycline on granulocyte migration was investigated on patients undergoing fracture surgery. The granulocyte migration of the patients was depressed when doxycycline was administered. Scanning electron microscopy demonstrated a decreased granulocyte adherence to glass as well as a decrease in number of filopods per cell in the presence of doxycycline.

Cell Adhesion↗