Biomedical subjects

J Rousselet

Publications and source records attributed to J Rousselet.

At least 19 recordsLinked to original sources

PubMed2006

Comparative population genetic study of two oligophagous insects associated with the same hosts.

A parallel study of the genetic structure of two oligophagous species associated with the same hosts was conducted to determine the main factors shaping the distribution of genetic diversity. The bark beetle Tomicus piniperda and the pine processionary moth (PPM) Thaumetopoea pityocampa are both associated with the genus Pinus and belong to different guilds (xylophagous vs defoliating species). The PPM is an ectophagous species that feeds on the needles of living trees, whereas T. piniperda is endophagous and bores galleries in the inner bark of weakened trees. Both species were sampled in the main regions of France, and their genetic structure was assessed after genotyping with five microsatellite markers. Populations of the PPM were significantly structured. A pattern of isolation by distance was found when distances were calculated as bypassing the Massif Central, whereas no such pattern could be found with raw geographic distances. On the contrary, most populations of T. piniperda were not differentiated. No effect of host species could be detected in either of the two species. We conclude that the two taxa have contrasting effective dispersal rates per generation, and we hypothesize that this reflects the different selection pressures acting on individual fitness via different strategies of host use.

Animals↗

PubMed2000

Chromosome fission associated with growth of ribosomal DNA in Neodiprion abietis (Hymenoptera: Diprionidae).

The haploid complement consists of seven metacentric chromosomes in most diprionid species but has evolved to n = 8 by fission in Neodiprion abietis. This fission generated a small telocentric chromosome and a large pseudoacrocentric chromosome with a short arm carrying a satellite. In situ hybridization indicated that the location of the rRNA gene cluster corresponds to the whole short arm. This suggests that (i) the breaking point was located close to an rRNA gene cluster, and (ii) fission was associated with growth of rDNA. These results suggest rDNA as a preferential breaking point but with a role in the healing of naked chromosome ends.

Animals↗

PubMed1998

The chromosomes of Diprion pini and D. similis (Hymenoptera: Diprionidae): implications for karyotype evolution.

Earlier cytological investigations characterize the family Diprionidae with a modal chromosome number of seven. This study shows that Diprion pini and D. similis have 14 acrocentric chromosomes (n = 14 for haploid males and 2n = 28 for diploid females). In D. pini, rRNA genes are located on the satellite and the round short arm of the chromosome carrying this segment. We studied six populations with no evidence of chromosomal polymorphism at the species level. Our results disagree with those published previously and reopen the question of karyotype evolution. Chromosome morphology, ISH and C-banding results support the hypothesis of chromosome number doubling by centric fission and not by polyploidization, followed by the growth of short arms by means of pericentromeric DNA amplification.

Animals↗

PubMed1994

Directional motion of brownian particles induced by a periodic asymmetric potential.

Structures possessing spatial asymmetry should act as pumps in the presence of dissipation alone, without the need for macroscopic forces or temperature differences to drive vectorial motion. It has been shown theoretically that particles subjected to an asymmetric periodic potential can display net directional motion even if the space-averaged force is zero. Here we demonstrate such behaviour experimentally. We have studied the behaviour of colloidal particles suspended in solution and exposed to a sawtooth dielectric potential which is turned on and off periodically. The particles exhibit net motion with a velocity that depends on their size, suggesting applications in separation processes for objects in the size range 0.1-5 microns--a range that includes biological structures such as viruses, cells and chromosomes. We furthermore point out the analogy between our device and motor protein assemblies.

Colloids↗

PubMed1983

[Incomplete dissolution of calculi. Calcification, cholecystectomy, after treatment of biliary lithiasis with chenodeoxycholic acid].

Among 54 patients with radiolucent asymptomatic gallstones treated by chenodeoxycholic acid (CDCA), 32 failures were observed. In 15 cases the size of gallstones did not change. In 11 cases the size of gallstones decreased but dissolution was not complete. In 6 cases the treatment had to be interrupted early because of the side-effects. In 10 patients (8.7 p. 100 of the treated patients) calcifications of gallstones occurred. In 9 patients (16.7 p. 100), a cholecystectomy had to be performed because of complications. The incidence of biliary complications necessitating cholecystectomy was significantly higher (p less than 0.001) in patients in whom CDCA failed to induce changes in gallstone size than in patients in whom CDCA was successful. Overall, a decrease of gallstones size was observed in 61 p. 100 of the 54 treated patients. However complete dissolution occurred in only two thirds of these patients. Patients in whom gallstone size decreased seldom presented with a biliary complication. Our data suggest that, when no obvious diminution of gallstones size is evident within six months of treatment, it is not advisable to continue the administration of CDCA. In case of failure, the responsibility of CDCA in the appearance of calcifications or even of complications necessitating cholecystectomy has to be discussed.

Calcinosis↗

PubMed1979