Epidermal expression of apolipoprotein E gene during fin and scale development and fin regeneration in zebrafish.

Apolipoprotein E (apoE) plays an important role in systemic and local lipid homeostasis. We have examined the expression of apoE during morphogenesis and regeneration of paired and unpaired fins and during scale development in zebrafish (Danio rerio). In situ hybridization analysis revealed that, during embryogenesis, apoE is expressed in the epithelial cells of the median fin fold and of the pectoral fin buds. ApoE remains expressed in the elongating fin folds throughout development of the fins. During the larval to juvenile transition, apoE transcripts were present in the distal, interray and lateral epidermis of developing fins. Furthermore, as scale buds started to form, apoE was expressed in large scale domains which later, became restricted to the external posterior epidermal part of scales. A low level of transcripts could be observed at later developmental stages at these locations probably because fins and scales continue to grow throughout the animal's life. During regeneration of both pectoral and caudal fins, a marked increase in apoE expression is observed as early as 12 hours after amputation in the wound epidermis. High levels of apoE transcripts are then localized primarily in the basal cell layer of the apical epidermis. The levels of apoE expression were maximum between the second to fourth days and then progressively declined to basal level by day 14. ApoE transcripts were also observed in putative macrophages infiltrated in the mesenchymal compartment of regenerating fins a few hours after amputation. In conclusion, apoE is highly expressed in the epidermis of developing fins and scales and during fin regeneration while no expression can be detected in the skin of the trunk. ApoE may play a specific role in fin and scale differentiation at sites where important epidermo-dermal interactions occur for the elaboration of the dermal skeleton and/or for lipid uptake and redistribution within these rapidly growing structures.

Expression of two even-skipped genes eve1 and evx2 during zebrafish fin morphogenesis and their regulation by retinoic acid.

Growth and patterning during fin regeneration depend, like for fin development, on the integrated expression of homeogenes. In the present work we have studied, by in situ hybridization, the expression and regulation of two vertebrate homologs eve1 and evx2 of the Drosophila pair-rule even-skipped gene family. Upon amputation of pectoral and caudal fins, both genes, expressed transiently in the mesenchyme during early stages of fin development of these fins, are turned on. During the formation of the blastema they are transcribed first in the mesenchyme located underneath the wound epidermis and then, their expression is restricted to the regenerating rays regions. These expression patterns are developmentally regulated since both genes are no longer transcribed when the bony rays are differentiating. Exposure of the regenerates to retinoic acid (RA) modifies the boundaries of eve1 and evx2 expression: the signal is down-regulated in the ray region and up-regulated in the interray region. Moreover, expression is induced in the wound epidermis. These results indicate that eve1 and evx2 products are part of the molecular signals involved in pattern formation of the fin and fin rays in connection with outgrowth. RA might alter growth and morphogenesis of the regenerating fins by a fine regulation of these genes among others.

Caudal fin regeneration in wild type and long-fin mutant zebrafish is affected by retinoic acid.

Zebrafish (Danio rerio) represents an ideal experimental model to tackle fundamental issues concerned with organogenesis during development and regeneration of complex body structures. We discuss here the development of the skeleton in zebrafish caudal fins, their regenerative ability in wild type and long-fin mutant adult fish, and how retinoic acid (RA), which induces duplications along the proximodistal axis in regenerating limbs, affects regeneration of the caudal fin. The dorsal and ventral lobes of zebrafish caudal fins are apparently symmetrical along the dorsoventral axis, but all of the skeletal elements and most of the soft tissues of both lobes originate from the ventral part of the embryo, as demonstrated by whole-mount staining of developing fish. Analysis of caudal fin regenerates in wild type adults does not reveal any difference in the regenerative ability of the two lobes, and in the length of the regenerate in comparison with the amputated part. In contrast, in the long-fin mutant the regenerated caudal fin is always somehow defective in that the original asymmetry in the length of the two lobes observed in this mutant is not reproduced in the regenerate. Furthermore, in the majority of the batches studied the regenerate is much smaller in size than the amputated part. This suggests that this mutant may be valuable to further our understanding of the mechanisms underlying growth control and patterning during regeneration. Finally, we show that the regenerating caudal fin is sensitive to RA-treatment, and clear teratogenic effects on the dorso-ventral axis are observed under many of the experimental conditions investigated both in wild type and long-fin mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning and expression of ferritin mRNA in heavy metal-poisoned Xenopus laevis cells.

In a search for genes transcriptionally regulated by metal ions, we have isolated a Xenopus laevis ferritin cDNA clone, XL2-17, from cadmium-poisoned XL2 cells. The large size of the corresponding ferritin mRNA (1.4 kb) is due to the presence of a 629-nucleotide 5'-untranslated region. The Xenopus ferritin sequence is highly isologous with other vertebrate ferritins. In particular, there is a complete sequence identity for the iron-responsive element (IRE) located in the 5'-untranslated region in both XL2-17 and Rana catesbeiana ferritin mRNAs. The position of this IRE is unusual since it is located 489 nucleotides from the 5' end of the ferritin mRNA. Our analysis of phylogenetic relationships among ferritins indicates that all amphibian ferritins thus far sequenced would be more closely related to the mammalian H-type ferritin than to the L-type. The level of ferritin mRNA in XL2 cells rises 10- to 15-fold following exposure of cells to cadmium or copper. This increase is due to both transcriptional and translational regulation. A 10-fold increase was also found at the protein level. These results suggest that ferritin may be a primary detoxification response to heavy metals in Xenopus cells.

In vitro effect of a glycopeptide acting in vivo on hepatocyte cell cycle.

A factor specifically inhibiting the hepatocyte cell cycle in vivo was found to block the G1-S transition of liver cells in vitro. It proved to be non-toxic in our culture conditions, as judged by the reversibility of the effect on cell proliferation. It was not active on DNA synthesis in fibroblastic cell lines (3T3).

[Action of broken fractions of regeneration blastema on the synthetic activity of posterior fragments or Dendrocelum lacteum cut behind the pharynx]. / Action de broyats de blastémes de régénération sur l'activité synthétique de fragments postérieurs de planaires Dendrocoelum lacteum, sectionnées en arriére du pharynx

Pounded blastemas of regeneration favour RNA synthesis is neoblasts of posterior parts of Dendrocoelum lacteum, cut behind the pharynx, which normally fail to regenerate a head; and induce excrescences. Fixed parenchyma cells and other differentiated tissues do not synthesize RNA with pounded blastemas.