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J C Mounolou

Publications and source records attributed to J C Mounolou.

At least 19 recordsLinked to original sources
PubMed1999

Mitochondrial genes collectively suggest the paraphyly of Crustacea with respect to Insecta.

Complete sequences of seven protein coding genes from Penaeus notialis mitochondrial DNA were compared in base composition and codon usage with homologous genes from Artemia franciscana and four insects. The crustacean genes are significantly less A + T-rich than their counterpart in insects and the pattern of codon usage (ratio of G + C-rich versus A + T-rich codon) is less biased. A phylogenetic analysis using amino acid sequences of the seven corresponding polypeptides supports a sister-taxon status for mollusks-annelid and arthropods. Furthermore, a distance matrix-based tree and two most-parsimonious trees both suggest that crustaceans are paraphyletic with respect to insects. This is also supported by the inclusion of Panulirus argus COII (complete) and COI and COIII (partial) sequence data. From analysis of single and combined genes to infer phylogenies, it is observed that obtained from single genes are not well supported in most topologies cases and notably differ from that of the tree based on all seven genes.

Animals↗
PubMed1997

Nonneutral evolution of tandem repeats in the mitochondrial DNA control region of lagomorphs.

The mitochondrial DNA of the European rabbit (Oryctolagus cuniculus) contains a tandem array of 153-bp repeats in the vicinity of the replication origin of the H-stand. Variation among molecules in the number of these repeats results in inter- and intraindividual length polymorphism (heteroplasmy). Generally, in an individual, one predominant molecular type is observed, the others representing a low percentage of the mtDNA content. At the tissue level, we observe a particular distribution of this polymorphism in the gonads compared with liver, kidneys, or brain, implying a relationship between the differentiation status of the cells and the types of new mtDNA molecules which appear and accumulate during lifetime. Similar tandem repeats were also found in the mtDNA noncoding region of European hares (Lepus europaeus), a cottontail (Sylvilagus floridanus), and a pika (Ochotona rufescens). The lengths and the sequences of these units evolve rapidly and in a concerted way, but the number of repeats is maintained in a narrow range, and an internal 20-bp segment is highly conserved. Constraints restrict the evolution of the primary sequence of these repeated units, the number of which is probably controlled by a stabilizing selection.

Animals↗
PubMed1997

[History of the rabbit and ancient DNA].

Present populations of Rabbits (Oryctolagus cuniculus) are organized into two well defined groups A and B according to their mitochondrial DNA sequences. Group A is restricted to the South Western part of the Iberian Peninsula while group B is found everywhere else. Domestic breeds belong to the latter. As evidenced from data on ancient bones (up to 12,000 years BP) the mitochondrial type B1, predominant in domestic animals, originated from Spain. B1 animals were introduced in France by man between late Roman times and Middle Ages.

Animals↗
PubMed1996

Partial sequence of the shrimp Penaeus notialis mitochondrial genome.

About half of the mitochondrial DNA of the shrimp Penaeus notialis (Crustacea: Decapoda) has been cloned (in 2 overlapping fragments of 7.9 kb and 1 kb) and partially sequenced. The gene content and arrangement are identical to that of the homologous domain in Drosophila yakuba. Intergenic nucleotides are scarce and a 982 bp non-coding sequence exhibit features similar to that of mtDNA control regions. The gene organization and the tRNA structures differentiate the Penaeus notialis mitochondrial genome from that of Artemia franciscana. Paraphyletism of crustacean mtDNA with respect to Insecta is discussed. A secondary structure of s-rRNA is proposed.

Animals↗
PubMed1995

Rabbit mitochondrial DNA diversity from prehistoric to modern times.

The mitochondrial genetic variability in European rabbit (Oryctolagus cuniculus) populations present in Europe and North Africa from 11,000 years ago to the present day has been analyzed using ancient DNA techniques. DNA was extracted from 90 rabbit bones found in 22 archaeological sites dated between the Mesolithic and recent times. Nucleotide sequences present in a variable 233-bp domain of the cytochrome b gene were compared to those present in modern-day rabbits. The results show that the structure of ancient populations of wild rabbit exhibited remarkable stability over time until the Middle Ages. At this time, a novel type of mtDNA molecule abruptly appears into most wild populations studied from France. This mtDNA type corresponds to that currently present in the domestic breeds of rabbit examined so far. The relative rapidity by which this mtDNA type established and its absence in all sites examined before 1,700 years ago lend support to the hypothesis that between 2,000 and 1,000 years ago, man may have favored the development, into all regions of France, of animals carrying this particular mtDNA molecule. The origin of such animals has still to be found: animals previously living outside of France or within France but in very restricted areas? This event was concomitant with the documented establishment of warrens after the tenth century A.D. in Europe.

Africa, Northern↗
PubMed1994

Ancient DNA from Bronze Age bones of European rabbit (Oryctolagus cuniculus).

The European rabbit (Oryctolagus cuniculus) is now widely distributed throughout the world as a result of transportation by man. The original populations, however, were confined to southern France and Spain. In order to investigate the role of human intervention in determining the genetic diversity of rabbit populations, we are studying the origin of rabbits introduced onto a small Mediterranean island (Zembra) near Tunis over 1400 years ago, by examining ancient DNA extracted from rabbit bones found both on Zembra and on the European mainland. Ancient DNA was successfully extracted from rabbit bones found at two archaeological sites dated to at least the Early Bronze Age (more than 3500 years ago) in south-central France, and compared to that found in modern mainland and island populations using a small variable region of the cytochrome b gene. The results confirm that the Zembra Island population is descended from that present over 1400 years ago. The technical aspects of DNA extraction from bones and the implications of this type of research for determining the origin of introduced rabbit populations are discussed.

Animals↗
PubMed1994

Genetic analysis of systematic mitochondrial heteroplasmy in rabbits.

One unusual property of rabbit mitochondrial DNA (mtDNA) is the existence of repeated 153-bp motifs in the vicinity of the replication origin of its H strand. Furthermore, every individual is heteroplasmic: it carries mtDNA molecules with a variable number of repeats. A systematic study of 8 females and their progeny has been devised to analyze mtDNA transmission through generations. The results suggest that three mechanisms are acting simultaneously. (1) Genetic drift in the germ line is revealed by the evolution of heteroplasmy when two major molecular forms are present in a female. (2) A high mutation rate (around 10(-2) per animal generation) generating molecular diversity, by deletion and addition of repeated units, is required to explain the observation of heteroplasmy in every individual. Moreover, the rates of mutation from the most frequent type to the other types are unequal. The deletion of one unit is more frequent than a deletion of two units, which is in turn more frequent than a deletion of three. (3) Selection for shorter molecules in somatic cells is probable. The frequency distribution of mtDNA types depends on the organ analyzed (kidney-spleen and liver vs. gonads).

Animals↗
PubMed1991

Cytochemical evidence of an organized microtubular cytoskeleton in Xenopus laevis oocytes: involvement in the segregation of mitochondrial populations.

An organized microtubular cytoskeleton was discovered in the cytoplasm of Xenopus laevis oocytes. The microtubules were observed in 10- to 30-micron cryostat sections by indirect immunoperoxidase labeling using an antibody to tubulin. A gradual extraction of cells with a nonionic detergent was essential for good penetration of the antibody into the cells. In the cytoplasm of all previtellogenic oocytes, a dense network of criss-crossed long microtubules was associated in a basket-like structure surrounding the mitochondrial mass. At the beginning of vitellogenesis, the network meshes enlarged, while clusters of mitochondria migrated, in close association with microtubule bundles. At the beginning of vitellogenesis, the reorganization of the microtubular network, mostly in the vegetal hemisphere, occurred during the segregation of the mitochondrial populations. Reorganization is characterized by (1) a temporary enlargement of the network and close association of mitochondrial clusters with microtubular bundles, and (2) a progressive organization of a ring-shaped microtubular structure in the crown elaboration area. It is hypothesized that these modifications of the microtubular cytoskeleton contribute to the maintenance of cell shape and the polarized organization of the cell.

Animals↗
PubMed1991

Mitochondrial biogenesis in rabbit articular chondrocytes transferred to culture.

The effect of the switch to aerobic growth conditions was examined in rabbit articular chondrocytes transferred to culture. Spectroscopic analysis of the cytochromes of the respiratory chain shows that only cytochrome b is present in chondrocytes from cartilage, cytochromes c, c1, and a.a3 being undetectable as compared with the typical spectrum found in a primary cell culture on day 4. Steady state levels of RNA transcripts of nuclear (cytochrome c) and mitochondrial genes (cytochrome b and cytochrome oxidase subunits II and III) involved in the oxidative metabolism were determined relative to the RNA transcripts of the nuclear gene for glyceraldehyde phosphate dehydrogenase involved in the glycolytic pathway and to mitochondrial ribosomal RNAs. Chondrocytes transferred to culture showed a general increase in the levels of all transcripts, but the effect on mitochondrial transcripts was much greater (x 20) than the effect on nuclear transcripts (x 3-4). These results show the absence of a coordinate regulation of the expression of mitochondrial and nuclear genes coding for components of the respiratory chain. The increase in mitochondrial DNA triggered by culture conditions does not appear to be sufficient to account for the enhanced transcription. Concomitant with these mitochondrial changes, the level of transcripts for the collagen II gene involved in the differentiation function decreases dramatically (3% of the control on day 3).

Animals↗
PubMed1990

Direct repeats in the non-coding region of rabbit mitochondrial DNA. Involvement in the generation of intra- and inter-individual heterogeneity.

In rabbit we observed heteroplasmy at an exceptionally high level, the heterogeneity occurring within the non-coding region of the DNA. Mitochondrial DNA (mt DNA) was cloned in pBR322 and the nucleotide sequence analysis of an EcoRI-Hind III fragment encompassing the non-coding region revealed that although there are common features with other mammalian mtDNAs (termed large central-conserved-sequence block, conserved-sequence blocks 1, 2 and 3 and termination-associated elements) the non-coding region shows an unusual organization; two stretches of tandem repeats of 20 bp and 153 bp are present in a part containing the origin of H-strand replication (OH) and probably the promoters for transcription as judged from other vertebrates. The long repeats are located between tRNA(Phe) and conserved sequence block 3 and the short repeats are located between conserved sequence blocks 1 and 2. When cloned in Escherichia coli (recA or recBC sbcb) DNA fragments containing the short repeats show length differences corresponding to various copy numbers of repeats. Electrophoretic analysis of the appropriate restriction fragments of rabbit mtDNA reveals extended intra- and inter-individual length heterogeneity. Both sets of repeats are involved in the generation of heterogeneity and are present in variable copy numbers from one mtDNA molecule to another. Moreover, rearrangement of the motives of the short repeat are observed to different extents in the mtDNA from one animal to another. The occurrence, maintenance and possible involvement of these repeated sequences, capable of forming stable secondary structures, are discussed in relation to their location in the region of control signals.

Amino Acid Sequence↗
PubMed1989

Mitochondrial gene expression during Xenopus laevis development: a molecular study.

Mitochondrial gene expression has been analysed during embryonic development of Xenopus laevis; the relative amounts of 12S and 16S ribosomal RNAs and of most mitochondrial messenger RNAs were determined by slot-blot and Northern-blot hybridization experiments with specific mitochondrial DNA probes. The rRNA content per embryo remained constant during early development, confirming earlier results of Chase and Dawid (1972, Dev. Biol., 27, 504-518.); on the contrary, all mRNAs decreased abruptly after fertilization within a few hours (by a factor of 5-10), remained at a very low level up to the late neurula stages and increased again during organogenesis. Since the mitochondrial DNA content does not vary during this period molecular analyses as well as biological observations suggest that the mitochondrial genome is completely inactivated at the beginning of embryonic development. The amounts of rRNAs and mRNAs evolve therefore as a function of time only according to their half-lives. Mitochondrial RNA accumulation resumes subsequently with a high rate when the general transcription in the embryo is starting again, and this occurs before the resumption of DNA replication in the organelle. It appears that the Xenopus embryonic development represents a quite clear example of regulation of the mitochondrial expression at the level of transcription.

Animals↗
PubMed1989

The generation of transplasmic Drosophila simulans by cytoplasmic injection: effects of segregation and selection on the perpetuation of mitochondrial DNA heteroplasmy.

Experimental transplasmic Drosophila simulans were obtained through cytoplasm microinjection between eggs carrying different mitochondrial genomes. These genomes (siII and siIII) show a 1.5% difference in their sequences. They produced a large number of heteroplasmic flies in their F1 progeny and several flies were still heteroplasmic at the eighth generation. The distribution of frequencies of mitochondrial genotypes in the offspring of heteroplasmic females suggests that the stochastic processes involved in the evolution of experimental heteroplasmy of multiple nucleotide sites are very similar to those previously described for spontaneous length heteroplasmy. In addition, the siII genome has a noticeable advantage over the siIII genome in both directions of injection. This advantage is estimated at 58% per fly generation and 5% per cell generation.

Animals↗
PubMed1989

Compared flow cytometric analysis of mitochondria using 10-n-nonyl acridine orange and rhodamine 123.

The use of the supravital mitochondrial-specific dye Rhodamine 123 (Rh 123) in combination with flow cytometry permits the monitoring of the changes in the mitochondrial transmembrane potential, reflecting the overall mitochondrial activity of the living cell. While this probe appears to be a potent tool for these studies, it also exhibits an important limit in the interpretation of the results: it cannot distinguish between an increase in mitochondrial activity without biogenesis and a modification of mitochondrial content. 10-n-Nonyl Acridine Orange chloride (NAO) constitutes another mitochondrial specific fluorochrome. In contrast with Rh 123, NAO accumulation in the cell does not seem to be driven by the proton-motrice force but does seem to be related to specific interactions with mitochondrial membrane proteins and/or lipids. In this work, the cytotoxicity of NAO, the kinetics of cellular uptake and the release of the dye have been determined using flow cytometry. The use of several ionophores or mitochondrial inhibitors has confirmed the independence of NAO uptake regarding mitochondrial transmembrane potential. NAO was also used to examine the changes in the mitochondrial compartment during the transfer of articular chondrocytes from cartilage to the culture conditions, where Rh 123 evidenced changes in mitochondrial activity and/or biogenesis, in order to know whether the use of probes with different specificity allows one to distinguish between mitochondrial activity and biogenesis.

Acridine Orange↗
PubMed1987

Sequence deduced physical properties in the D-loop region common to five vertebrate mitochondrial DNAs.

Some sequence-induced physical properties of the region of the replication origin in human, mouse, rat, ox and xenopus mitochondrial DNA have been studied: characteristic profiles of stability can be observed, a consensus pattern of hydrogen bond donor/acceptor associated to a symmetrical distribution of base roll angles variation is found upstream of the 5' ends of the D-loop strand. In spite of diversity, evolution has conserved the collective physical properties in parts of the origin of replication region suggesting specific functions for these non-coding sequences.

Animals↗
PubMed1987

Rhodamine 123 uptake and mitochondrial DNA content in rabbit articular chondrocytes evolve differently upon transfer from cartilage to culture conditions.

Mitochondrial DNA (mtDNA) represents 0.15% of the total cell DNA (at least an order of magnitude less than in liver or heart) of rabbit articular chondrocytes. Besides the already well-documented low respiratory activity, chondrocyte differentiation thus involves a specific control of mitochondrial biogenesis. When transferred to in vitro conditions, chondrocytes increase their stock of mtDNA at the same time they resume growth, even more efficiently (8 times) than they do for cell volume (4.4 times). On the contrary, overall mitochondrial activity, estimated as the uptake of rhodamine 123, does not follow the same trend (2.5 times increase). Chondrocytes apparently keep these functional characteristics for some generations in culture.

Animals↗
PubMed1987

Segregation of mitochondria in the cytoplasm of Xenopus vitellogenic oocytes.

In actively growing vitellogenic oocytes of Xenopus laevis mitochondria segregate into 2 populations. One stays around the nucleus, actively replicates mitochondrial DNA (mtDNA), and builds up most of the stock of the mitochondria in the full-grown oocyte. The other moves toward the vegetal pole and stops replicating mtDNA early in vitellogenesis. Organelles of this population are components of the germ plasm of the cell.

Animals↗
PubMed1986

Mitochondrial uptake of rhodamine 123 by rabbit articular chondrocytes.

Rhodamine 123 was used to stain and analyze by flow cytometry the mitochondria of rabbit articular chondrocytes. Stationary primary cultures and exponentially growing subcultures were compared to enzymatically released chondrocytes from cartilage. The increase in mitochondrial fluorescence, when chondrocytes are transferred from cartilage to culture environment, is suggestive of some change in chondrocyte adaptation and/or differentiation in these conditions.

Animals↗