Biomedical subjects

J Michaux

Publications and source records attributed to J Michaux.

12 recordsLinked to original sources

PubMed2003

Contribution of collagen stable isotope biogeochemistry to the paleobiology of extinct endemic vertebrates from Tenerife (Canary Islands, Spain).

The paleodiet and paleoenvironmental context of two extinct species from Tenerife island, one giant rat Canariomys bravoi and one giant lizard Gallotia goliath, have been investigated using carbon and nitrogen isotopic compositions of fossil bone collagen. Preliminary to this study, a calibration of the isotopic variations of bone collagen from modern Rat Rattus rattus, Rabbit Oryctolagus cuniculus and Lizard Gallotia galotti relative to environmental conditions on Tenerife Islands has been attempted. No clear relationship could be found between collagen delta13C and delta15N values and aridity; the only relevant factors seem to be seashore proximity for rat, and the relative amount of C3 and CAM plants. It seems that anthropic activities have interfered with the expected relationships between collagen isotopic compositions and environmental conditions. Most fossil specimens yielded well preserved collagen. The isotopic composition of giant rat and giant lizard collagen suggest a purely C3 environment, possibly more humid than today on Tenerife. Large ranges of nitrogen isotopic compositions, especially within giant rats, may be due to local environmental conditions. Further work is needed in order to provide more valuable paleobiological information in order to better understand the role of environmental factors in the evolution and extinction of insular endemic species on Tenerife.

Animals↗

PubMed2001

Evolutionary history of the most speciose mammals: molecular phylogeny of muroid rodents.

Phylogenetic relationships between 32 species of rodents representing 14 subfamilies of Muridae and four subfamilies of Dipodidae were studied using sequences of the nuclear protein-coding genes Lecithin Cholesterol Acyl Transferase (LCAT) and von Willebrand Factor (vWF). An examination of some evolutionary properties of each data matrix indicates that the two genes are rather complementary, with lower rates of nonsynonymous substitutions for LCAT. Both markers exhibit a wide range of GC3 percentages (55%-89%), with several taxa above 70% GC3 for vWF, which indicates that those exonic regions might belong to the richest class of isochores. The primary sequence data apparently harbor few saturations, except for transitions on third codon positions for vWF, as indicated by comparisons of observed and expected pairwise values of substitutions. Phylogenetic trees based on 1,962 nucleotidic sites from the two genes indicate that the 14 Muridae subfamilies are organized into five major lineages. An early isolation leads to the clade uniting the fossorial Spalacinae and semifossorial Rhizomyinae with a strong robustness. The second lineage includes a series of African taxa representing nesomyines, dendromurines, cricetomyines, and the sole living member of mystromyines. The third one comprises only the mouselike hamster CALOMYSCUS: The fourth clade represents the cricetines, myospalacines, sigmodontines, and arvicolines, whereas the fifth one comprises four "traditional" subfamilies (Gerbillinae, Murinae, Otomyinae, and Acomyinae). Within these groups, we confirm the monophyly of almost all studied subfamilies, namely, Spalacinae, Rhizomyinae, Nesomyinae, Cricetomyinae, Arvicolinae, Sigmodontinae, Cricetinae, Gerbillinae, Acomyinae, and Murinae. Finally, we present evidence that the sister group of Acomyinae is Gerbillinae, and we confirm a nested position of Myospalacinae within Cricetinae and Otomyinae within Murinae. From a biogeographical point of view, the five main lineages spread and radiated from Asia with different degrees of success: the first three groups are now represented by a limited number of species and genera localized in some regions, whereas the last two groups radiated in a large variety of species and genera dispersed all over the world.

Animals↗

PubMed2000

The bushlike radiation of muroid rodents is exemplified by the molecular phylogeny of the LCAT nuclear gene.

Phylogenetic relationships among 40 extant species of rodents, with an emphasis on the taxonomic sampling of Muridae and Dipodidae, were studied using sequences of the nuclear protein-coding gene LCAT (lecithin cholesterol acyl transferase). Analysis of 804 bp from the exonic regions of LCAT confirmed many traditional groupings in and around Muridae. A strong support was found for the families Muridae (represented by 29 species) and Dipodidae (5 species). Compared with Sciuridae, Gliridae, and Caviomorpha, the Dipodidae family appeared the closest relative of Muridae, confirming the suprafamilial Myodonta concept. Within the speciose family Muridae, the first branching leads to the fossorial Spalacinae and semifossorial Rhyzomyinae. The remaining components of Muridae appear as a polytomy from which are issued Sigmodontinae, Calomyscinae, Arvicolinae, Cricetinae, Mystromyinae, Nesomyinae, and some Dendromurinae (Steatomys and Dendromus). This phylogeny is interpreted as the result of a bushlike radiation at the end of the early Miocene, leading to emergence of most living subfamilies. The separation between three additional taxa, Murinae, Gerbillinae, and "Acomyinae" (which comprises the genera Acomys, Deomys, Uranomys, and Lophuromys), has occurred more recently from a common ancestor issued from the main basal radiation. As previously shown by other molecular studies, the vlei rats, Otomyinae, are nested within Old World Murinae. In the same way, the zokors, Myospalacinae, appear strongly nested within the hamsters, Cricetinae. Finally, we propose a sister group relationship between Malagasy Nesomyinae and south African Mystromyinae.

Animals↗

PubMed1999

Novel mutant green fluorescent protein protease substrates reveal the activation of specific caspases during apoptosis.

BACKGROUND: The caspase-mediated proteolysis of many cellular proteins is a critical event during programmed cell death or apoptosis. It is important to determine which caspases are activated in mammalian cells, and where and when activation occurs, upon receipt of specific death stimuli. Such information would be useful in the design of strategies to regulate the activation of caspases during apoptosis. RESULTS: We developed two novel fluorescent substrates that were specifically cleaved by caspase-1 or caspase-3. For in vitro studies, four-amino-acid recognition sequences, YVAD for caspase-1 and DEVD for caspase-3, were introduced between blue fluorescent protein (BFP) and green fluorescent protein (GFP), expressed in bacteria and purified. For in vivo studies, YVAD and DEVD were introduced between cyan fluorescent protein and yellow fluorescent protein, and expression was monitored in live mammalian cells. The proximity between fluorophores was determined using fluorescence resonance energy transfer. Purified substrates were cleaved following exposure to purified caspase-1 and caspase-3. In Cos-7 cells, caspase-1 and caspase-3 substrates were cleaved upon induction of apoptosis with staurosporine, a protein-kinase inhibitor, whereas caspase-3 but not caspase-1 substrate was cleaved upon treatment of cells with the DNA-damaging agent mitomycin c. CONCLUSIONS: These substrates allow the spatial activation of specific members of the caspase family to be deciphered during the initiation and execution phase of programmed cell death, and allow activation of specific caspases to be monitored both in vivo and in vitro. This technology is also likely to be useful for high-throughput screening of reagents that modulate caspase activity.

Animals↗

PubMed1998

[Recent history of the brown bear in the Maghreb].

Bones of the brown bear (Ursus arctos, mammalia, Carnivora) found in a cave of the Akouker massif (Djurdjura, Algeria) have been dated according to the 14C method as belonging to the historical times (420-600 A.D.). The bone and teeth measurements correspond to a small-sized animal, the smallest ever found in the Maghreb. A review of fossil bears in the Quaternary faunas of North Africa clearly shows that the area of distribution, which was initially wide, shrank at the end of the Upper Pleistocene. The bears had temporarily taken to mountainous areas difficult to access. The bone remains discovered up to now prove that the brown bear was represented by individuals or populations showing a large diversity of size.

Algeria↗

PubMed1993

Molecular evidence that the spiny mouse (Acomys) is more closely related to gerbils (Gerbillinae) than to true mice (Murinae).

Spiny mice of the genus Acomys traditionally have been classified as members of the Murinae, a subfamily of rodents that also includes rats and mice with which spiny mice share a complex set of morphological characters, including a unique molar pattern. The origin and evolution of this molar pattern, documented by many fossils from Southern Asia, support the hypothesis of the monophyly of Acomys and all other Murinae. This view has been challenged by immunological studies that have suggested that Acomys is as distantly related to mice (Mus) as are other subfamilies (e.g., hamsters: Cricetinae) of the muroid rodents. We present molecular evidence derived from DNA.DNA hybridization data that indicate that the spiny mouse Acomys and two African genera of Murinae, Uranomys and Lophuromys, constitute a monophyletic clade, a view that was recently suggested on the basis of dental characters. However, our DNA.DNA hybridization data also indicate that the spiny mice (Acomys) are more closely related to gerbils (Gerbillinae) than to the true mice and rats (Murinae) with which they have been classified. Because Acomys and the brush-furred mice Uranomys and Lophuromys share no derived morphological characters with the Gerbillinae, their murine morphology must have evolved by convergence, including the molar pattern previously considered to support the monophyly of the Murinae.

Animals↗

PubMed1980

[Bridge grafting between the ascending and lower thoracic aorta using the right side approach (author's transl)].

We describe a method aimed at reconstituting the thoracic aorta by means of a graft located on the right side of the heart. The method is original in that the graft is entirely intra-thoracic and not thoraco-abdominal, as in previously reported similar operations, its advantages are demonstrated by reference to one case where it was used for the treatment of a relapsed congenital atresia of the aortic arch.

Adolescent↗

PubMed1972