Reproduction, nutrition, development最新文献

Recent evolutions of somatic cloning by nuclear transfer are reported, especially in the bovine species where potential applications are underway for biomedicine in association with transgenesis, or for agriculture by improving livestock. The overall efficiency of this biotechnology remains low in terms of viable offspring, but significant progress has been achieved on the different steps of the technique. However, the in vivo development of bovine blastocysts derived from somatic nuclear transfer is characterised by some important features that lead to the "cloning syndrome". Important losses occur during the peri-implantation period and further late foetal loss is observed in association with the Large Offspring Syndrome. About 60-70% of the cloned calves born survive normally to the adult stage and present an apparently normal physiology. Recent data already available on bovine somatic clones of both sexes indicate that they have a zootechnical performance similar to non cloned animals and they are able to reproduce normally without the pathologies associated to cloning thus confirming that the deviations observed in clones are of epigenetic origin and not transmitted to the progeny.

Normal gametogenesis and steroidogenesis is highly dependent on the pulsatile release of hypothalamic GnRH that binds high-affinity receptors present at the surface of pituitary gonadotrophs thereby triggering the synthesis and release of the gonadotropins LH and FSH. The mammalian GnRH receptor displays the classical heptahelical structure of G protein-coupled receptors with, however, a unique feature, the lack of a C-terminal tail. Accordingly, it does not desensitise sensu stricto, and internalises very poorly. It is now well established that GnRH stimulation induces the activation of a complex network of transduction pathways involved in the control of gonadotropin release and subunit gene expression. Other authors and ourselves have demonstrated that the GnRH action is associated with an increased complexity regarding gene regulation/cell function. Indeed GnRH affects the GnRH receptor gene itself and a number of additional genes that include some involved in cell signalling and auto-/paracrine regulation. The fact that GnRH regulates the expression of its own receptor, together with a host of other genes typically involved in its signal transduction cascades implies alteration/auto-adaptation in gonadotropic responsiveness. Furthermore, some of these genes respond differentially depending on whether the GnRH stimulation is intermittent or permanent suggesting specific roles in the dual process of activation/desensitisation. Thus, it can be assumed that the importance of pulsatility of GnRH action is closely related to, or dependent on, the inability of the GnRH receptor to desensitise. Moreover, multiple post-receptor events are crucial for both the regulation/plasticity of gonadotropic function and the maintenance of cell integrity.

Transgenesis has become an essential tool for the study of gene expression mechanisms and functions. Transgenesis is also more and more used for biotechnological applications such as the study of human diseases, the adaptation of pig organs to humans, the production of pharmaceutical proteins in milk and likely in the future for the improvement of animal production. The use of transgenesis relies on the efficiency of gene transfer. New tools have been recently designed to improve gene transfer. The methods of gene transfer are highly dependent on the techniques of animal reproduction. Conversely, the need to improve transgenesis urges researchers to study some of the key steps in reproduction and to find new techniques for gene transfer. This paper summarises the recent data and the perspectives offered by animal transgenesis.

In this review, we describe recent results concerning the genetics of sex determination in mammals. Particularly, we developed the study of the FOXL2 gene and its implication in genetic anomalies in goats (PIS mutation) and humans (BPES). We present the expression of FOXL2 in the ovaries of different species.

The development of the four generations of Reproductive Biotechnology, particularly in cattle and since the last world war, represents one of the best examples of the success story of technology transfer. This review will only refer to the first three generations and will not deal with nuclear transfer nor transgenesis. Based on sound so-called "finalised" research, Artificial Insemination first, then in vivo collected embryo transfer and later in vitro fertilised embryo transfer have been implemented worldwide. Each of these Biotechnologies has many advantages and limitations. In addition to the specificity of each of them, one major point is that farmers and breeders may choose either collectively or individually, the best technology to be used in order to achieve the goals they have set for their industry. It is noteworthy that these technologies have been able to match with the economics demands over the last decades and yet are in a very good capacity to respond to the contemporary demand of sustainable development. In this context, there are further advantages such as potentially contributing to maintaining biodiversity or allowing preservation ex situ of genes otherwise threatened to extinction.

Compared to mammals, teleost reproduction presents many original features. Reproductive strategies of species are diversified into numerous adaptations to a large variety of aquatic environments. This diversity may concern sexuality, spawning and parental behaviour, sensitivity to environmental factors, and specific features of gametogenesis such as the duration of vitellogenesis, and egg morphology. Sexuality presents a variety of natural modalities, from gonochorism to hermaphrodism. The absence of definitive arrest of body growth in the adult of most species gives a particular interest to the practical control of growth-reproduction interactions. Vitellogenesis, which represents an important metabolic effort for the maternal organism, involves the synthesis of vitellogenin, a specific glycolipo-phosphoprotein produced in the liver under estradiol stimulation, and its incorporation into oocytes by a receptor mediated process. Both estradiol synthesis in follicle cells and vtg uptake by vitellogenic follicles appear to be mainly controlled by FSH. Oocyte maturation is directly triggered by a progestin, or MIS (maturation inducing steroid) synthesised in follicle cells mainly under LH control, and acting through the non-genomic activation of a membrane receptor. Practical applications of some of these particularities result mainly from the external character of the fertilisation process and of embryonic development, which allows manipulating respectively egg chromosome stocks and sex differentiation. Moreover, the sensitivity of sex differentiation to exogenous factors favours the development of practical methods to control the sex of farmed populations. Finally, the sensitivity of reproductive mechanisms to xenobiotics has led to various kinds of bioassays for putative pollutants.

It is difficult to harmonise faith and the desire to follow religious teachings and obligations on the one hand, and scientific advances and their use for the benefit of suffering humanity on the other. This is an especially delicate matter for patients and health professionals in reproductive medicine. It deals with the conflicting issues of contraception, termination of pregnancy, assisted reproduction, cloning, stem cells and embryo research. Beyond the technical aspects of these matters, the theoretical, legal, philosophical and religious implications must be explored, including the concepts of personality, individuality, human dignity, autonomy, beneficence and justice. Most importantly, an analysis must be made of the beginnings of a human being, the protection it deserves, the concept and time of ensoulment, the need for pragmatism and the right of transgression (hence the title of this article).

Natural eCG consists of as much as 45% carbohydrate side chains. The present paper deals with the analysis of the roles of the N- and O-linked saccharides of this hormone in the different steps of its activity and its possible replacement by recombinant eCG expressed in baculovirus-insect cell systems.

"Reflexive biology", using the ambiguities of the term, is altogether a biology that plays with the mirrors of the different levels of organisation, which, endlessly, go from one place to another, organisms in their real environment to the genome via cells in vitro and others, but which is also reflexive because at any moment biology reflects the finalities and the worry of what it should serve.