Ci-hox12 tail gradient precedes and participates in the control of the apoptotic-dependent tail regression during Ciona larva metamorphosis.

At the onset of the Ciona intestinalis metamorphosis, the first event is tail regression characterized, by a contraction, an apoptotic wave and Primordial Germ Cells (PGC) movement. All these cell behaviors originate from the posterior tail tip and progress to the anterior. Interestingly, earlier in Ciona development, the antero-posterior (A/P) patterning of the tailbud epidermis depends on two antagonist gradients, respectively FGF/MAPK at the posterior and retinoic acid (RA) at the anterior part of the tail. Fundamental genes such as Ci-hox1, Ci-hox12 and Ci-wnt5, classically involved in chordates A/P polarity and patterning, are controlled by these gradients and exhibit specific expression profiles in the tail epidermis. In this study, we first confirmed by video-microscopy that tail regression depends on a postero-anterior wave of a caspase-dependent apoptosis coupled with a contraction event. Concomitantly an apoptotic-dependent postero-anterior movement of PGC was observed for the first time. Unexpectedly, we observed that expression of the posterior hox gene, Ci-hox12, was extended from a posterior localization to the entire tail epidermis as the larvae progress from the swimming period to the settlement stage. In addition, when we disturbed FGF/MAPK or RA gradients we observed strong effects on Ci-hox12 expression pattern coupled with modulation on the subsequent tail regression dynamics. These results support the idea that Ci-hox12 expression in larval tail precedes and participates in the regulation of the postero-anterior cell behavior during the subsequent tail regression.

A molecular phylogeny shows the single origin of the Pyrenean subterranean Trechini ground beetles (Coleoptera: Carabidae).

Trechini ground beetles include some of the most spectacular radiations of cave and endogean Coleoptera, but the origin of the subterranean taxa and their typical morphological adaptations (loss of eyes and wings, depigmentation, elongation of body and appendages) have never been studied in a formal phylogenetic framework. We provide here a molecular phylogeny of the Pyrenean subterranean Trechini based on a combination of mitochondrial (cox1, cyb, rrnL, tRNA-Leu, nad1) and nuclear (SSU, LSU) markers of 102 specimens of 90 species. We found all Pyrenean highly modified subterranean taxa to be monophyletic, to the exclusion of all epigean and all subterranean species from other geographical areas (Cantabrian and Iberian mountains, Alps). Within the Pyrenean subterranean clade the three genera (Geotrechus, Aphaenops and Hydraphaenops) were polyphyletic, indicating multiple origins of their special adaptations to different ways of life (endogean, troglobitic or living in deep fissures). Diversification followed a geographical pattern, with two main clades in the western and central-eastern Pyrenees respectively, and several smaller lineages of more restricted range. Based on a Bayesian relaxed-clock approach, and using as an approximation a standard mitochondrial mutation rate of 2.3% MY, we estimate the origin of the subterranean clade at ca. 10 MY. Cladogenetic events in the Pliocene and Pleistocene were almost exclusively within the same geographical area and involving species of the same morphological type.

Antioxidant activity of hemocyanin; a pulse radiolysis study.

In order to determine the reactivity on hemocyanin from Androctonus australis, the reaction of superoxide anion has been investigated using pulse radiolysis. The kinetics of O2- decays have been studied in aqueous buffered media at various basic pH (8, 8.5 and 9), first in the absence and then in the presence of hemocyanin (in oxygenated solutions containing formate anion 0.16 mol.l-1). We have shown that, in the presence of hemocyanin, O2- decay is a first-order process whose apparent rate constant is proportional to protein concentration (10(-7) to 10(-6) mol.l-1) and pH independent between 8 to 9. A second-order rate constant of 3.5 +/- 0.1.10(7) mol-1.l.s-1, has been deduced for the catalytic rate constant of hemocyanin with O2-. Meanwhile, this activity is smaller than that described for free copper, eukaryotic Cu-Zn-SOD or some copper chelates. We have verified that apohemocyanin--the copper deprived protein--does not exhibit such an activity vs. SOD (superoxide dismutase).

Induction of double-strand breaks in Chinese hamster ovary cells at two different dose rates of gamma-irradiation.

Using pulsed-field gel electrophoresis (PFGE) analysis we investigated the existence of a dose rate effect of gamma-irradiation on the measured presence of DNA double-strand breaks (DSB) in a repair competent (K1) and a repair deficient (mutant xrs6) Chinese hamster ovary (CHO) cell line. The fraction of DNA fragments released from cells embedded in agarose during PFGE after gamma-irradiation was taken as a measure of DSB induction. In CHO-K1 cells DSB were present at a significantly higher rate when gamma-irradiation was delivered at a high dose rate of 22 Gy/min (HDR) than at a medium dose rate of 0.45 Gy/min (MDR) at 37 degrees C. However, the same amount of DSB was found when irradiation was performed at the two dose rates at 4 degrees C. The DSB yield was also identical at both dose rates in the DSB repair deficient mutant xrs6. The results indicate that there is an apparent dose rate effect for gamma-ray induced DSB in repair competent CHO cells due to partial repair of DSB taking place during gamma-ray exposures at MDR but not at HDR. This repair of DSB was inhibited upon irradiation at 4 degrees C and in repair deficient xrs6 cells.

Barnacle duplicate engrailed genes: divergent expression patterns and evidence for a vestigial abdomen.

Cirripedes (barnacles) are crustaceans that are characterized by a very peculiar body plan, in particular by the lack of an abdomen. To study their body plan, we searched for their engrailed gene. We found two engrailed (en.a/en.b) genes in cirripedes. The two engrailed genes of the rhizocephalan barnacle Sacculina carcini are expressed in the posterior compartment of developing segments and appendages. When the neuroectoderm differentiates into epidermis and neuroderm the expression patterns of en.a and en.b diverge dramatically. en.a expression fades in segment epidermis whereas it is subsequently detected ventrally in reiterated putative neural cells. At the same time, en.b expression increases in the epidermis, which makes it a very good segmentation marker. Five tiny en.b stripes are observed between the sixth thoracic segment and the telson. We interpret these stripes as the molecular definition of vestigial abdominal segments, being the remnant of an ancestral state in keeping with the bodyplan of maxillopod crustaceans. engrailedexpression is the first molecular evidence for a segmented abdomen in barnacles.

Cloning and expression of the engrailed.a gene of the barnacle Sacculina carcini.

Cirripedia (barnacles) constitute a crustacean monophyletic taxon which is very well defined by several synapomorphies. In particular, all cirripedes are composed of six thoracic segments, but are devoid of any complete abdominal segment. This body plan is preserved in the adult in non-parasitic groups, while the parasitic rhizocephalan cirripedes completely lose arthropodian segmentation at the adult stage. These traits make them a particularly favourable model for studying the formation and maintenance of segmental identity. For the above reasons, it seemed worthwhile to look at the segmentation gene engrailed in a cirripede. A complete engrailed.a cDNA was isolated from larvae of the rhizocephalan cirripede Sacculina carcini. Its expression was monitored during larval development by use of the monoclonal antibody MAb4D9 directed against the Drosophila homologous proteins. The Sacculina engrailed.a gene is expressed during the second and third larval stages in stripes within a posterior area corresponding to the presumptive trunk segments. Surprisingly, these stripes appear in a posterior to anterior sequence. Six engrailed.a stripes characterize the thoracic segments of the cirripedean ground plan.