The three-dimensional roughness of stylolites in limestones: roughness analysis and possible genetic implications

International audienceStylolites are dynamic roughly planar surfaces formed by pressure solution of blocks of rocks into each other. The three-dimensional geometry of 12 bedding-parallel stylolites in several limestones was measured using laser and mechanical profilometers, and statistical characteristics of the surfaces were calculated. All the stylolites analyzed turn out to have self-affine fractal roughness with a well-characterized crossover length scale separating two self-affine regimes. Strikingly, this characteristic length scale falls within a very narrow range for all the stylolites studied, regardless of the microstructure sizes. To explain the data, we propose a continuous phenomenological model that accounts for the development of the measured roughness from an initially flat surface. The model postulates that the complex interface morphology is the result of competition between the long-range elastic redistribution of local stress fluctuations, which roughen the surface, and surface tension forces along the interface, which smooth it. The model accounts for the geometrical variability of stylolite surfaces and predicts the dependence of the crossover length scale on the mechanical properties of the rock

Nuclear transfer: Progress and quandaries

Cloning mammals by nuclear transfer is a powerful technique that is quickly advancing the development of genetically defined animal models. However, the overall efficiency of nuclear transfer is still very low and several hurdles remain before the power of this technique will be fully harnessed. Among these hurdles include an incomplete understanding of biologic processes that control epigenetic reprogramming of the donor genome following nuclear transfer. Incomplete epigenetic reprogramming is considered the major cause of the developmental failure of cloned embryos and is frequently associated with the disregulation of specific genes. At present, little is known about the developmental mechanism of reconstructed embryos. Therefore, screening strategies to design nuclear transfer protocols that will mimic the epigenetic remodeling occurring in normal embryos and identifying molecular parameters that can assess the developmental potential of pre-implantation embryos are becoming increasingly important. A crucial need at present is to understand the molecular events required for efficient reprogramming of donor genomes after nuclear transfer. This knowledge will help to identify the molecular basis of developmental defects seen in cloned embryos and provide methods for circumventing such problems associated with cloning the future application of this technology

Animal cloning and its contribution to veterinary research

Cloning is a technique currently used mainly for research purposes , to understand how the nucleus of a differentiated cell can, once it has been placed into the cytoplasm of an enucleated ovule, can re-acquiresthe properties of an embryonic nucleus.The rate of full term development in cloned embryos is still low, only about 5 per cent of the reconstructed embryos.However, it is now well established that clones can develop into adults with a seemingly normal physiology, as fertile animals with the same life span as animals born from sexual reproduction. In cattle, widely used as a cloning model, recent data has shown that clones’ zootechnic performances are similar, and in some instances less variable than those of animals born from a fertilised egg.In this species, cloning failures are due to early (first trimester of gestation) as well as late (last trimester of gestation) embryo and foetal mortality. Approximately 30% of clones are born with a complex lethal syndrome, known as the Large Offspring Syndrome (LOS), with a bodyweight greater than normal, placentomes in lower numbers and oedematous, and physiological disorders resulting in cardiovascular, respiratory, immune, or hepato-renal dysfunctions. Animals with this syndrome generally die within two months from birth.Current research focuses on the clinical follow-up of the gestation of clones and on embryological studies, which showed that such disorders often stem from a growth deregulation in the foetal tissues and organs.Molecular analysis of these epigenetic disorders should help understand better the ontogenesis of the body’s main functions.The study of clones shows that the programme which leads to the development of a complex living being is both robust and flexible, and that its reinitialising when introducing the somatic nucleus within the ovule cytoplasm is probably not required.Le clonage est une technique utilisée aujourd'hui essentiellement en recherche pour comprendre comment un noyau de cellules différenciées peut, une fois placé dans l'environnement cytoplasmique d'un ovule énucléé, acquérir à nouveau des propriétés de noyau embryonnaire. Le taux de développement à terme des embryons clonés est aujourd'hui toujours faible, inférieur à cinq pour cent. Il est toutefois maintenant bien établi que les clones peuvent se développer en adultes d'apparence physiologique normale, être fertiles et avoir la même durée de vie que des animaux obtenus par reproduction sexuée. Chez le bovin, largement utilisé comme modèle, des données récentes montrent que les performances zootechniques des clones sont semblables et pour certains caractères, moins variables que celles d'animaux issus de fécondation. Chez cette espèce, les échecs du clonage sont dus à des mortalités embryonnaires et foetales précoces (premier tiers de la gestation) mais aussi tardives (pendant le dernier tiers de la gestation). Environ 30 % des clones présentent à la naissance un syndrome létal complexe, le syndrome LOS, caractérisé notamment par un poids supérieur à la normale, des placentomes oedémateux en nombre réduit et des perturbations physiologiques se traduisant par des dysfonctionnements systémiques affectant soit les système cardiovasculaire, respiratoire ou immunitaire ou encore le fonctionnement hépato-rénal. Les animaux affectés par ce syndrome meurent en général dans les deux mois qui suivent la naissance. Les recherches en cours donnent une large place au suivi clinique des gestations de clones et aux études embryologiques. Elles montrent que ces perturbations ont souvent pour origine des dérégulations de la croissance des tissus et organes foetaux. L'analyse moléculaire de ces perturbations épigénétiques devrait permettre de mieux connaître l'ontogenèse des grandes fonctions de l'organisme. L'étude des clones montre que le programme de développement qui permet la construction d'un organisme vivant complexe est à la fois robuste et flexible et que sa réinitialisation au moment où l'on introduit le noyau somatique dans le cytoplasme de l'ovule n'est sans doute pas requise

Early alteration of the self-renewal/differentiation threshold in trophoblast stem cells derived from mouse embryos after nuclear transfer

Development after nuclear transfer (NT) is subjected to defects originating from both the epiblast and the trophoblast parts of the conceptus and is always accompanied by placentomegaly at term. Here we have investigated the origin of the reprogramming errors affecting the trophoblast lineage in mouse NT embryos. We show that trophoblast stem (TS) cells can be derived from NT embryos (ntTS cells) and used as an experimental in vitro model of trophoblast proliferation and differentiation. Strikingly, TS derivation is more efficient from NT embryos than from controls and ntTS cells exhibit a growth advantage over control TS cells under self-renewal conditions. While epiblast-produced growth factors Fgf4 and Activin exert a fine-tuned control on the balance between self-renewal and differentiation of control TS cells, ntTS cells exhibit a reduced dependency upon their micro-environment. Since the supply of growth factors is known do decrease at the onset of placental formation in vivo we propose that TS cells in NT embryos continue to self-renew during a longer period of time than in fertilized embryo. The resulting increased pool of progenitors could contribute to the enlarged extra-embryonic region observed in the early trophoblast of in vivo grown mouse NT blastocysts that results in placentomegaly

A repetitive probe for FISH analysis of bovine interphase nuclei

The purpose of this study was to generate repetitive DNA sequence probes for the analysis of interphase nuclei by fluorescent in situ hybridisation (FISH). Such probes are useful for the diagnosis of chromosomal abnormalities in bovine preimplanted embryos. Of the seven probes (E1A, E4A, Ba, H1A, W18, W22, W5) that were generated and partially sequenced, five corresponded to previously described Bos taurus repetitive DNA (E1A, E4A, Ba, W18, W5), one probe (W22) shared no homology with other DNA sequences and one (H1A) displayed a significant homology with Rattus norvegicus mRNA for secretin receptor transmembrane domain 3. Fluorescent in situ hybridisation was performed on metaphase bovine fibroblast cells and showed that five of the seven probes hybridised most centromeres (E1A, E4A, Ba, W18, W22), one labelled the arms of all chromosomes (W5) and the H1A probe was specific to three chromosomes (ch14, ch20, and ch25). Moreover, FISH with H1A resulted in interpretable signals on interphase nuclei in 88% of the cases, while the other probes yielded only dispersed overlapping signals