Abnormalities in bovine conceptus development during the embryonic phase after In Vitro Fertilization (IVF) and cloning by nuclear transfer (NT)
Assis Neto, Antônio Chaves deGaldos, Álvaro RiveirosMançanares, Ana Carolina FurlanettoAlberto, Míryan Lança ViliaAmbrósio, Carlos EduardoFavaron, Phelipe OliveiraMeirelles, Flavio VieiraMiglino, Maria Angelica
Background: Embryonic mortality is a major cause of reproductive failure in cattle, resulting in a lot of problems to the industry. Recently, many techniques have been used in the production of genetically modified animals mainly related to improve the animal production. The possibility to genetically manipulate living organisms through the addition or inactivation of genes has revolutionized the understanding of biological and molecular mechanisms. Herein, we showed data about what is known about the abnormalities in bovine conceptus using IVF and NT techniques. Review: The establishment of pregnancy results from the interaction between the trophoblast and maternal tissues. Embryonic/ fetal loss occurs throughout pregnancy in cattle; however, it is concentrated mainly in the first 42 days after breeding. Recently data have showed that approximately 50% of cloned bovine embryos do not establish the gestation after the transference of the blastocyst. In addition, placental abnormalities occur in high levels in cloned animals during the initial and in the end of gestation. Low viability of cloned embryos is mainly expressed by the reduction in the rate of deployment, the increased rate of perinatal mortality and fetal, and the various anomalies observed in newborn animals. Among the pregnancy complications from placental transfer of manipulated embryos (IVF and NT) there are changes in the morphology of the placentome, in the region of the fetal-maternal contact, increase of allantoic or amniotic fluid, vascularity, lower number of cotyledons, and increased of the interplacentomal area "Offspring Syndrome". In addition, the placenta, fetal membranes and umbilical cord from cloned animals have rudimentary development. According to Wells et al., the overall efficiency of cloning in bovine is limited to 5- 6%. In IVF pregnancies the placentome percentage, fetal villi, density and volume of binucleated cells is reduced. However, the volume of blood vessels in increased maternal wattles, believing there is a compensatory mechanism in the vascular network of the placentae. Conclusion: Many technological innovations could help to obtain a better quality production and significant improvements in animal breeding such as those brought about by nuclear transfer and in vitro fertilization. New studies on the dynamics of development in cattle embryology derived from nuclear transfer techniques and in vitro fertilization are necessary, focusing on different systems in order to find greater success in the artificial producing and selection of interest characteristics.
Texto completo