Nuclear transfer: a new tool for reproductive biotechnology in cattle

Abstract

-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. biotechnology / reproduction / cattle / somatic cloning / nuclear transfer / efficiency

Massive dysregulation of genes involved in cell signaling and placental development in cloned cattle conceptus and maternal endometrium

“…Our model is strongly supported by the observed progressive loss of clones throughout pregnancy (27,28), with major postimplantation spikes occurring at d 30 and d 60 of gestation. Losses later in pregnancy are associated with placentomegaly and hydrallantois, which are a result of placental dysfunction.…”

“…Thus, multiple lines of experimental evidence have led to the conclusion that EET is the origin of the developmental pathologies in placentation of SCNTderived clones (17,(22)(23)(24)(25)(26). Therefore, study of the communication between cloned conceptuses and the endometrium should yield important insights into the mechanisms underlying average losses of ∼60% of cloned embryos before implantation and 80% of fetuses within the first trimester of gestation (27,28).…”

“…In SCNT pregnancies, an additional 30-100% of clones are lost after implantation, depending on the cell line used (27,28,45). These losses are typically accompanied by abnormal placental development, with fewer, enlarged, and edematous placentomes [reviewed by Chavatte-Palmer et al (12)].…”

Evaluation of laser-assisted lentiviral transgenesis in bovine

“…Combined with targeted transgenesis via homologous recombination in somatic donor cells the creation of transgenic and expressing livestock became possible . But also NT was shown to suffer from low efficiencies and the resulting offspring often exhibitvarious developmental abnormalities, which are commonly summarized as "large offspring syndrome (LOS)" (Heyman, 2005).…”

<b>Modificações epigenéticas da cromatina e sua relação com a reprogramação nuclear de bovinos<b>

“…Diversos trabalhos têm relacionado essa baixa eficiência ao estado de diferenciação da célula doadora de núcleo, uma vez que as taxas de gestação de células mais 50 diferenciadas são menores quando comparadas àquelas menos especializadas (HEYMAN, 2005 A dificuldade em apagar a memória epigenética da célula somática tem sido apontada como uma das principais causas da baixa eficiência da técnica. Um exemplo que demonstra isso, é que as iPS diferenciam com muito mais facilidade para o mesmo tipo celular do qual a célula reprogramada foi isolada inicialmente .…”